summaryrefslogtreecommitdiffstats
path: root/vendor/cc/src/lib.rs
blob: 1ebd2cc7a577ca3f3bbb1fe024fec31b03c769c7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
//! A library for build scripts to compile custom C code
//!
//! This library is intended to be used as a `build-dependencies` entry in
//! `Cargo.toml`:
//!
//! ```toml
//! [build-dependencies]
//! cc = "1.0"
//! ```
//!
//! The purpose of this crate is to provide the utility functions necessary to
//! compile C code into a static archive which is then linked into a Rust crate.
//! Configuration is available through the `Build` struct.
//!
//! This crate will automatically detect situations such as cross compilation or
//! other environment variables set by Cargo and will build code appropriately.
//!
//! The crate is not limited to C code, it can accept any source code that can
//! be passed to a C or C++ compiler. As such, assembly files with extensions
//! `.s` (gcc/clang) and `.asm` (MSVC) can also be compiled.
//!
//! [`Build`]: struct.Build.html
//!
//! # Parallelism
//!
//! To parallelize computation, enable the `parallel` feature for the crate.
//!
//! ```toml
//! [build-dependencies]
//! cc = { version = "1.0", features = ["parallel"] }
//! ```
//! To specify the max number of concurrent compilation jobs, set the `NUM_JOBS`
//! environment variable to the desired amount.
//!
//! Cargo will also set this environment variable when executed with the `-jN` flag.
//!
//! If `NUM_JOBS` is not set, the `RAYON_NUM_THREADS` environment variable can
//! also specify the build parallelism.
//!
//! # Examples
//!
//! Use the `Build` struct to compile `src/foo.c`:
//!
//! ```no_run
//! fn main() {
//!     cc::Build::new()
//!         .file("src/foo.c")
//!         .define("FOO", Some("bar"))
//!         .include("src")
//!         .compile("foo");
//! }
//! ```

#![doc(html_root_url = "https://docs.rs/cc/1.0")]
#![cfg_attr(test, deny(warnings))]
#![allow(deprecated)]
#![deny(missing_docs)]

use std::collections::{hash_map, HashMap};
use std::env;
use std::ffi::{OsStr, OsString};
use std::fmt::{self, Display, Formatter};
use std::fs;
use std::hash::Hasher;
use std::io::{self, BufRead, BufReader, Read, Write};
use std::path::{Component, Path, PathBuf};
use std::process::{Child, Command, Stdio};
use std::sync::{Arc, Mutex};
use std::thread::{self, JoinHandle};

// These modules are all glue to support reading the MSVC version from
// the registry and from COM interfaces
#[cfg(windows)]
mod registry;
#[cfg(windows)]
#[macro_use]
mod winapi;
#[cfg(windows)]
mod com;
#[cfg(windows)]
mod setup_config;
#[cfg(windows)]
mod vs_instances;

pub mod windows_registry;

/// A builder for compilation of a native library.
///
/// A `Build` is the main type of the `cc` crate and is used to control all the
/// various configuration options and such of a compile. You'll find more
/// documentation on each method itself.
#[derive(Clone, Debug)]
pub struct Build {
    include_directories: Vec<PathBuf>,
    definitions: Vec<(String, Option<String>)>,
    objects: Vec<PathBuf>,
    flags: Vec<String>,
    flags_supported: Vec<String>,
    known_flag_support_status: Arc<Mutex<HashMap<String, bool>>>,
    ar_flags: Vec<String>,
    asm_flags: Vec<String>,
    no_default_flags: bool,
    files: Vec<PathBuf>,
    cpp: bool,
    cpp_link_stdlib: Option<Option<String>>,
    cpp_set_stdlib: Option<String>,
    cuda: bool,
    cudart: Option<String>,
    target: Option<String>,
    host: Option<String>,
    out_dir: Option<PathBuf>,
    opt_level: Option<String>,
    debug: Option<bool>,
    force_frame_pointer: Option<bool>,
    env: Vec<(OsString, OsString)>,
    compiler: Option<PathBuf>,
    archiver: Option<PathBuf>,
    cargo_metadata: bool,
    link_lib_modifiers: Vec<String>,
    pic: Option<bool>,
    use_plt: Option<bool>,
    static_crt: Option<bool>,
    shared_flag: Option<bool>,
    static_flag: Option<bool>,
    warnings_into_errors: bool,
    warnings: Option<bool>,
    extra_warnings: Option<bool>,
    env_cache: Arc<Mutex<HashMap<String, Option<String>>>>,
    apple_sdk_root_cache: Arc<Mutex<HashMap<String, OsString>>>,
    emit_rerun_if_env_changed: bool,
}

/// Represents the types of errors that may occur while using cc-rs.
#[derive(Clone, Debug)]
enum ErrorKind {
    /// Error occurred while performing I/O.
    IOError,
    /// Invalid architecture supplied.
    ArchitectureInvalid,
    /// Environment variable not found, with the var in question as extra info.
    EnvVarNotFound,
    /// Error occurred while using external tools (ie: invocation of compiler).
    ToolExecError,
    /// Error occurred due to missing external tools.
    ToolNotFound,
    /// One of the function arguments failed validation.
    InvalidArgument,
}

/// Represents an internal error that occurred, with an explanation.
#[derive(Clone, Debug)]
pub struct Error {
    /// Describes the kind of error that occurred.
    kind: ErrorKind,
    /// More explanation of error that occurred.
    message: String,
}

impl Error {
    fn new(kind: ErrorKind, message: &str) -> Error {
        Error {
            kind: kind,
            message: message.to_owned(),
        }
    }
}

impl From<io::Error> for Error {
    fn from(e: io::Error) -> Error {
        Error::new(ErrorKind::IOError, &format!("{}", e))
    }
}

impl Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{:?}: {}", self.kind, self.message)
    }
}

impl std::error::Error for Error {}

/// Configuration used to represent an invocation of a C compiler.
///
/// This can be used to figure out what compiler is in use, what the arguments
/// to it are, and what the environment variables look like for the compiler.
/// This can be used to further configure other build systems (e.g. forward
/// along CC and/or CFLAGS) or the `to_command` method can be used to run the
/// compiler itself.
#[derive(Clone, Debug)]
pub struct Tool {
    path: PathBuf,
    cc_wrapper_path: Option<PathBuf>,
    cc_wrapper_args: Vec<OsString>,
    args: Vec<OsString>,
    env: Vec<(OsString, OsString)>,
    family: ToolFamily,
    cuda: bool,
    removed_args: Vec<OsString>,
}

/// Represents the family of tools this tool belongs to.
///
/// Each family of tools differs in how and what arguments they accept.
///
/// Detection of a family is done on best-effort basis and may not accurately reflect the tool.
#[derive(Copy, Clone, Debug, PartialEq)]
enum ToolFamily {
    /// Tool is GNU Compiler Collection-like.
    Gnu,
    /// Tool is Clang-like. It differs from the GCC in a sense that it accepts superset of flags
    /// and its cross-compilation approach is different.
    Clang,
    /// Tool is the MSVC cl.exe.
    Msvc { clang_cl: bool },
}

impl ToolFamily {
    /// What the flag to request debug info for this family of tools look like
    fn add_debug_flags(&self, cmd: &mut Tool, dwarf_version: Option<u32>) {
        match *self {
            ToolFamily::Msvc { .. } => {
                cmd.push_cc_arg("-Z7".into());
            }
            ToolFamily::Gnu | ToolFamily::Clang => {
                cmd.push_cc_arg(
                    dwarf_version
                        .map_or_else(|| "-g".into(), |v| format!("-gdwarf-{}", v))
                        .into(),
                );
            }
        }
    }

    /// What the flag to force frame pointers.
    fn add_force_frame_pointer(&self, cmd: &mut Tool) {
        match *self {
            ToolFamily::Gnu | ToolFamily::Clang => {
                cmd.push_cc_arg("-fno-omit-frame-pointer".into());
            }
            _ => (),
        }
    }

    /// What the flags to enable all warnings
    fn warnings_flags(&self) -> &'static str {
        match *self {
            ToolFamily::Msvc { .. } => "-W4",
            ToolFamily::Gnu | ToolFamily::Clang => "-Wall",
        }
    }

    /// What the flags to enable extra warnings
    fn extra_warnings_flags(&self) -> Option<&'static str> {
        match *self {
            ToolFamily::Msvc { .. } => None,
            ToolFamily::Gnu | ToolFamily::Clang => Some("-Wextra"),
        }
    }

    /// What the flag to turn warning into errors
    fn warnings_to_errors_flag(&self) -> &'static str {
        match *self {
            ToolFamily::Msvc { .. } => "-WX",
            ToolFamily::Gnu | ToolFamily::Clang => "-Werror",
        }
    }

    fn verbose_stderr(&self) -> bool {
        *self == ToolFamily::Clang
    }
}

/// Represents an object.
///
/// This is a source file -> object file pair.
#[derive(Clone, Debug)]
struct Object {
    src: PathBuf,
    dst: PathBuf,
}

impl Object {
    /// Create a new source file -> object file pair.
    fn new(src: PathBuf, dst: PathBuf) -> Object {
        Object { src: src, dst: dst }
    }
}

impl Build {
    /// Construct a new instance of a blank set of configuration.
    ///
    /// This builder is finished with the [`compile`] function.
    ///
    /// [`compile`]: struct.Build.html#method.compile
    pub fn new() -> Build {
        Build {
            include_directories: Vec::new(),
            definitions: Vec::new(),
            objects: Vec::new(),
            flags: Vec::new(),
            flags_supported: Vec::new(),
            known_flag_support_status: Arc::new(Mutex::new(HashMap::new())),
            ar_flags: Vec::new(),
            asm_flags: Vec::new(),
            no_default_flags: false,
            files: Vec::new(),
            shared_flag: None,
            static_flag: None,
            cpp: false,
            cpp_link_stdlib: None,
            cpp_set_stdlib: None,
            cuda: false,
            cudart: None,
            target: None,
            host: None,
            out_dir: None,
            opt_level: None,
            debug: None,
            force_frame_pointer: None,
            env: Vec::new(),
            compiler: None,
            archiver: None,
            cargo_metadata: true,
            link_lib_modifiers: Vec::new(),
            pic: None,
            use_plt: None,
            static_crt: None,
            warnings: None,
            extra_warnings: None,
            warnings_into_errors: false,
            env_cache: Arc::new(Mutex::new(HashMap::new())),
            apple_sdk_root_cache: Arc::new(Mutex::new(HashMap::new())),
            emit_rerun_if_env_changed: true,
        }
    }

    /// Add a directory to the `-I` or include path for headers
    ///
    /// # Example
    ///
    /// ```no_run
    /// use std::path::Path;
    ///
    /// let library_path = Path::new("/path/to/library");
    ///
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .include(library_path)
    ///     .include("src")
    ///     .compile("foo");
    /// ```
    pub fn include<P: AsRef<Path>>(&mut self, dir: P) -> &mut Build {
        self.include_directories.push(dir.as_ref().to_path_buf());
        self
    }

    /// Add multiple directories to the `-I` include path.
    ///
    /// # Example
    ///
    /// ```no_run
    /// # use std::path::Path;
    /// # let condition = true;
    /// #
    /// let mut extra_dir = None;
    /// if condition {
    ///     extra_dir = Some(Path::new("/path/to"));
    /// }
    ///
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .includes(extra_dir)
    ///     .compile("foo");
    /// ```
    pub fn includes<P>(&mut self, dirs: P) -> &mut Build
    where
        P: IntoIterator,
        P::Item: AsRef<Path>,
    {
        for dir in dirs {
            self.include(dir);
        }
        self
    }

    /// Specify a `-D` variable with an optional value.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .define("FOO", "BAR")
    ///     .define("BAZ", None)
    ///     .compile("foo");
    /// ```
    pub fn define<'a, V: Into<Option<&'a str>>>(&mut self, var: &str, val: V) -> &mut Build {
        self.definitions
            .push((var.to_string(), val.into().map(|s| s.to_string())));
        self
    }

    /// Add an arbitrary object file to link in
    pub fn object<P: AsRef<Path>>(&mut self, obj: P) -> &mut Build {
        self.objects.push(obj.as_ref().to_path_buf());
        self
    }

    /// Add an arbitrary flag to the invocation of the compiler
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .flag("-ffunction-sections")
    ///     .compile("foo");
    /// ```
    pub fn flag(&mut self, flag: &str) -> &mut Build {
        self.flags.push(flag.to_string());
        self
    }

    /// Add a flag to the invocation of the ar
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .file("src/bar.c")
    ///     .ar_flag("/NODEFAULTLIB:libc.dll")
    ///     .compile("foo");
    /// ```
    pub fn ar_flag(&mut self, flag: &str) -> &mut Build {
        self.ar_flags.push(flag.to_string());
        self
    }

    /// Add a flag that will only be used with assembly files.
    ///
    /// The flag will be applied to input files with either a `.s` or
    /// `.asm` extension (case insensitive).
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .asm_flag("-Wa,-defsym,abc=1")
    ///     .file("src/foo.S")  // The asm flag will be applied here
    ///     .file("src/bar.c")  // The asm flag will not be applied here
    ///     .compile("foo");
    /// ```
    pub fn asm_flag(&mut self, flag: &str) -> &mut Build {
        self.asm_flags.push(flag.to_string());
        self
    }

    fn ensure_check_file(&self) -> Result<PathBuf, Error> {
        let out_dir = self.get_out_dir()?;
        let src = if self.cuda {
            assert!(self.cpp);
            out_dir.join("flag_check.cu")
        } else if self.cpp {
            out_dir.join("flag_check.cpp")
        } else {
            out_dir.join("flag_check.c")
        };

        if !src.exists() {
            let mut f = fs::File::create(&src)?;
            write!(f, "int main(void) {{ return 0; }}")?;
        }

        Ok(src)
    }

    /// Run the compiler to test if it accepts the given flag.
    ///
    /// For a convenience method for setting flags conditionally,
    /// see `flag_if_supported()`.
    ///
    /// It may return error if it's unable to run the compiler with a test file
    /// (e.g. the compiler is missing or a write to the `out_dir` failed).
    ///
    /// Note: Once computed, the result of this call is stored in the
    /// `known_flag_support` field. If `is_flag_supported(flag)`
    /// is called again, the result will be read from the hash table.
    pub fn is_flag_supported(&self, flag: &str) -> Result<bool, Error> {
        let mut known_status = self.known_flag_support_status.lock().unwrap();
        if let Some(is_supported) = known_status.get(flag).cloned() {
            return Ok(is_supported);
        }

        let out_dir = self.get_out_dir()?;
        let src = self.ensure_check_file()?;
        let obj = out_dir.join("flag_check");
        let target = self.get_target()?;
        let host = self.get_host()?;
        let mut cfg = Build::new();
        cfg.flag(flag)
            .target(&target)
            .opt_level(0)
            .host(&host)
            .debug(false)
            .cpp(self.cpp)
            .cuda(self.cuda);
        if let Some(ref c) = self.compiler {
            cfg.compiler(c.clone());
        }
        let mut compiler = cfg.try_get_compiler()?;

        // Clang uses stderr for verbose output, which yields a false positive
        // result if the CFLAGS/CXXFLAGS include -v to aid in debugging.
        if compiler.family.verbose_stderr() {
            compiler.remove_arg("-v".into());
        }

        let mut cmd = compiler.to_command();
        let is_arm = target.contains("aarch64") || target.contains("arm");
        let clang = compiler.family == ToolFamily::Clang;
        command_add_output_file(
            &mut cmd,
            &obj,
            self.cuda,
            target.contains("msvc"),
            clang,
            false,
            is_arm,
        );

        // We need to explicitly tell msvc not to link and create an exe
        // in the root directory of the crate
        if target.contains("msvc") && !self.cuda {
            cmd.arg("-c");
        }

        cmd.arg(&src);

        let output = cmd.output()?;
        let is_supported = output.stderr.is_empty();

        known_status.insert(flag.to_owned(), is_supported);
        Ok(is_supported)
    }

    /// Add an arbitrary flag to the invocation of the compiler if it supports it
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .flag_if_supported("-Wlogical-op") // only supported by GCC
    ///     .flag_if_supported("-Wunreachable-code") // only supported by clang
    ///     .compile("foo");
    /// ```
    pub fn flag_if_supported(&mut self, flag: &str) -> &mut Build {
        self.flags_supported.push(flag.to_string());
        self
    }

    /// Set the `-shared` flag.
    ///
    /// When enabled, the compiler will produce a shared object which can
    /// then be linked with other objects to form an executable.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .shared_flag(true)
    ///     .compile("libfoo.so");
    /// ```
    pub fn shared_flag(&mut self, shared_flag: bool) -> &mut Build {
        self.shared_flag = Some(shared_flag);
        self
    }

    /// Set the `-static` flag.
    ///
    /// When enabled on systems that support dynamic linking, this prevents
    /// linking with the shared libraries.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .shared_flag(true)
    ///     .static_flag(true)
    ///     .compile("foo");
    /// ```
    pub fn static_flag(&mut self, static_flag: bool) -> &mut Build {
        self.static_flag = Some(static_flag);
        self
    }

    /// Disables the generation of default compiler flags. The default compiler
    /// flags may cause conflicts in some cross compiling scenarios.
    ///
    /// Setting the `CRATE_CC_NO_DEFAULTS` environment variable has the same
    /// effect as setting this to `true`. The presence of the environment
    /// variable and the value of `no_default_flags` will be OR'd together.
    pub fn no_default_flags(&mut self, no_default_flags: bool) -> &mut Build {
        self.no_default_flags = no_default_flags;
        self
    }

    /// Add a file which will be compiled
    pub fn file<P: AsRef<Path>>(&mut self, p: P) -> &mut Build {
        self.files.push(p.as_ref().to_path_buf());
        self
    }

    /// Add files which will be compiled
    pub fn files<P>(&mut self, p: P) -> &mut Build
    where
        P: IntoIterator,
        P::Item: AsRef<Path>,
    {
        for file in p.into_iter() {
            self.file(file);
        }
        self
    }

    /// Set C++ support.
    ///
    /// The other `cpp_*` options will only become active if this is set to
    /// `true`.
    pub fn cpp(&mut self, cpp: bool) -> &mut Build {
        self.cpp = cpp;
        self
    }

    /// Set CUDA C++ support.
    ///
    /// Enabling CUDA will pass the detected C/C++ toolchain as an argument to
    /// the CUDA compiler, NVCC. NVCC itself accepts some limited GNU-like args;
    /// any other arguments for the C/C++ toolchain will be redirected using
    /// "-Xcompiler" flags.
    ///
    /// If enabled, this also implicitly enables C++ support.
    pub fn cuda(&mut self, cuda: bool) -> &mut Build {
        self.cuda = cuda;
        if cuda {
            self.cpp = true;
            self.cudart = Some("static".to_string());
        }
        self
    }

    /// Link CUDA run-time.
    ///
    /// This option mimics the `--cudart` NVCC command-line option. Just like
    /// the original it accepts `{none|shared|static}`, with default being
    /// `static`. The method has to be invoked after `.cuda(true)`, or not
    /// at all, if the default is right for the project.
    pub fn cudart(&mut self, cudart: &str) -> &mut Build {
        if self.cuda {
            self.cudart = Some(cudart.to_string());
        }
        self
    }

    /// Set warnings into errors flag.
    ///
    /// Disabled by default.
    ///
    /// Warning: turning warnings into errors only make sense
    /// if you are a developer of the crate using cc-rs.
    /// Some warnings only appear on some architecture or
    /// specific version of the compiler. Any user of this crate,
    /// or any other crate depending on it, could fail during
    /// compile time.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .warnings_into_errors(true)
    ///     .compile("libfoo.a");
    /// ```
    pub fn warnings_into_errors(&mut self, warnings_into_errors: bool) -> &mut Build {
        self.warnings_into_errors = warnings_into_errors;
        self
    }

    /// Set warnings flags.
    ///
    /// Adds some flags:
    /// - "-Wall" for MSVC.
    /// - "-Wall", "-Wextra" for GNU and Clang.
    ///
    /// Enabled by default.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .warnings(false)
    ///     .compile("libfoo.a");
    /// ```
    pub fn warnings(&mut self, warnings: bool) -> &mut Build {
        self.warnings = Some(warnings);
        self.extra_warnings = Some(warnings);
        self
    }

    /// Set extra warnings flags.
    ///
    /// Adds some flags:
    /// - nothing for MSVC.
    /// - "-Wextra" for GNU and Clang.
    ///
    /// Enabled by default.
    ///
    /// # Example
    ///
    /// ```no_run
    /// // Disables -Wextra, -Wall remains enabled:
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .extra_warnings(false)
    ///     .compile("libfoo.a");
    /// ```
    pub fn extra_warnings(&mut self, warnings: bool) -> &mut Build {
        self.extra_warnings = Some(warnings);
        self
    }

    /// Set the standard library to link against when compiling with C++
    /// support.
    ///
    /// See [`get_cpp_link_stdlib`](cc::Build::get_cpp_link_stdlib) documentation
    /// for the default value.
    /// If the `CXXSTDLIB` environment variable is set, its value will
    /// override the default value, but not the value explicitly set by calling
    /// this function.
    ///
    /// A value of `None` indicates that no automatic linking should happen,
    /// otherwise cargo will link against the specified library.
    ///
    /// The given library name must not contain the `lib` prefix.
    ///
    /// Common values:
    /// - `stdc++` for GNU
    /// - `c++` for Clang
    /// - `c++_shared` or `c++_static` for Android
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .shared_flag(true)
    ///     .cpp_link_stdlib("stdc++")
    ///     .compile("libfoo.so");
    /// ```
    pub fn cpp_link_stdlib<'a, V: Into<Option<&'a str>>>(
        &mut self,
        cpp_link_stdlib: V,
    ) -> &mut Build {
        self.cpp_link_stdlib = Some(cpp_link_stdlib.into().map(|s| s.into()));
        self
    }

    /// Force the C++ compiler to use the specified standard library.
    ///
    /// Setting this option will automatically set `cpp_link_stdlib` to the same
    /// value.
    ///
    /// The default value of this option is always `None`.
    ///
    /// This option has no effect when compiling for a Visual Studio based
    /// target.
    ///
    /// This option sets the `-stdlib` flag, which is only supported by some
    /// compilers (clang, icc) but not by others (gcc). The library will not
    /// detect which compiler is used, as such it is the responsibility of the
    /// caller to ensure that this option is only used in conjunction with a
    /// compiler which supports the `-stdlib` flag.
    ///
    /// A value of `None` indicates that no specific C++ standard library should
    /// be used, otherwise `-stdlib` is added to the compile invocation.
    ///
    /// The given library name must not contain the `lib` prefix.
    ///
    /// Common values:
    /// - `stdc++` for GNU
    /// - `c++` for Clang
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .cpp_set_stdlib("c++")
    ///     .compile("libfoo.a");
    /// ```
    pub fn cpp_set_stdlib<'a, V: Into<Option<&'a str>>>(
        &mut self,
        cpp_set_stdlib: V,
    ) -> &mut Build {
        let cpp_set_stdlib = cpp_set_stdlib.into();
        self.cpp_set_stdlib = cpp_set_stdlib.map(|s| s.into());
        self.cpp_link_stdlib(cpp_set_stdlib);
        self
    }

    /// Configures the target this configuration will be compiling for.
    ///
    /// This option is automatically scraped from the `TARGET` environment
    /// variable by build scripts, so it's not required to call this function.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .target("aarch64-linux-android")
    ///     .compile("foo");
    /// ```
    pub fn target(&mut self, target: &str) -> &mut Build {
        self.target = Some(target.to_string());
        self
    }

    /// Configures the host assumed by this configuration.
    ///
    /// This option is automatically scraped from the `HOST` environment
    /// variable by build scripts, so it's not required to call this function.
    ///
    /// # Example
    ///
    /// ```no_run
    /// cc::Build::new()
    ///     .file("src/foo.c")
    ///     .host("arm-linux-gnueabihf")
    ///     .compile("foo");
    /// ```
    pub fn host(&mut self, host: &str) -> &mut Build {
        self.host = Some(host.to_string());
        self
    }

    /// Configures the optimization level of the generated object files.
    ///
    /// This option is automatically scraped from the `OPT_LEVEL` environment
    /// variable by build scripts, so it's not required to call this function.
    pub fn opt_level(&mut self, opt_level: u32) -> &mut Build {
        self.opt_level = Some(opt_level.to_string());
        self
    }

    /// Configures the optimization level of the generated object files.
    ///
    /// This option is automatically scraped from the `OPT_LEVEL` environment
    /// variable by build scripts, so it's not required to call this function.
    pub fn opt_level_str(&mut self, opt_level: &str) -> &mut Build {
        self.opt_level = Some(opt_level.to_string());
        self
    }

    /// Configures whether the compiler will emit debug information when
    /// generating object files.
    ///
    /// This option is automatically scraped from the `DEBUG` environment
    /// variable by build scripts, so it's not required to call this function.
    pub fn debug(&mut self, debug: bool) -> &mut Build {
        self.debug = Some(debug);
        self
    }

    /// Configures whether the compiler will emit instructions to store
    /// frame pointers during codegen.
    ///
    /// This option is automatically enabled when debug information is emitted.
    /// Otherwise the target platform compiler's default will be used.
    /// You can use this option to force a specific setting.
    pub fn force_frame_pointer(&mut self, force: bool) -> &mut Build {
        self.force_frame_pointer = Some(force);
        self
    }

    /// Configures the output directory where all object files and static
    /// libraries will be located.
    ///
    /// This option is automatically scraped from the `OUT_DIR` environment
    /// variable by build scripts, so it's not required to call this function.
    pub fn out_dir<P: AsRef<Path>>(&mut self, out_dir: P) -> &mut Build {
        self.out_dir = Some(out_dir.as_ref().to_owned());
        self
    }

    /// Configures the compiler to be used to produce output.
    ///
    /// This option is automatically determined from the target platform or a
    /// number of environment variables, so it's not required to call this
    /// function.
    pub fn compiler<P: AsRef<Path>>(&mut self, compiler: P) -> &mut Build {
        self.compiler = Some(compiler.as_ref().to_owned());
        self
    }

    /// Configures the tool used to assemble archives.
    ///
    /// This option is automatically determined from the target platform or a
    /// number of environment variables, so it's not required to call this
    /// function.
    pub fn archiver<P: AsRef<Path>>(&mut self, archiver: P) -> &mut Build {
        self.archiver = Some(archiver.as_ref().to_owned());
        self
    }
    /// Define whether metadata should be emitted for cargo allowing it to
    /// automatically link the binary. Defaults to `true`.
    ///
    /// The emitted metadata is:
    ///
    ///  - `rustc-link-lib=static=`*compiled lib*
    ///  - `rustc-link-search=native=`*target folder*
    ///  - When target is MSVC, the ATL-MFC libs are added via `rustc-link-search=native=`
    ///  - When C++ is enabled, the C++ stdlib is added via `rustc-link-lib`
    ///  - If `emit_rerun_if_env_changed` is not `false`, `rerun-if-env-changed=`*env*
    ///
    pub fn cargo_metadata(&mut self, cargo_metadata: bool) -> &mut Build {
        self.cargo_metadata = cargo_metadata;
        self
    }

    /// Adds a native library modifier that will be added to the
    /// `rustc-link-lib=static:MODIFIERS=LIBRARY_NAME` metadata line
    /// emitted for cargo if `cargo_metadata` is enabled.
    /// See https://doc.rust-lang.org/rustc/command-line-arguments.html#-l-link-the-generated-crate-to-a-native-library
    /// for the list of modifiers accepted by rustc.
    pub fn link_lib_modifier(&mut self, link_lib_modifier: &str) -> &mut Build {
        self.link_lib_modifiers.push(link_lib_modifier.to_string());
        self
    }

    /// Configures whether the compiler will emit position independent code.
    ///
    /// This option defaults to `false` for `windows-gnu` and bare metal targets and
    /// to `true` for all other targets.
    pub fn pic(&mut self, pic: bool) -> &mut Build {
        self.pic = Some(pic);
        self
    }

    /// Configures whether the Procedure Linkage Table is used for indirect
    /// calls into shared libraries.
    ///
    /// The PLT is used to provide features like lazy binding, but introduces
    /// a small performance loss due to extra pointer indirection. Setting
    /// `use_plt` to `false` can provide a small performance increase.
    ///
    /// Note that skipping the PLT requires a recent version of GCC/Clang.
    ///
    /// This only applies to ELF targets. It has no effect on other platforms.
    pub fn use_plt(&mut self, use_plt: bool) -> &mut Build {
        self.use_plt = Some(use_plt);
        self
    }

    /// Define whether metadata should be emitted for cargo to detect environment
    /// changes that should trigger a rebuild.
    ///
    /// This has no effect if the `cargo_metadata` option is `false`.
    ///
    /// This option defaults to `true`.
    pub fn emit_rerun_if_env_changed(&mut self, emit_rerun_if_env_changed: bool) -> &mut Build {
        self.emit_rerun_if_env_changed = emit_rerun_if_env_changed;
        self
    }

    /// Configures whether the /MT flag or the /MD flag will be passed to msvc build tools.
    ///
    /// This option defaults to `false`, and affect only msvc targets.
    pub fn static_crt(&mut self, static_crt: bool) -> &mut Build {
        self.static_crt = Some(static_crt);
        self
    }

    #[doc(hidden)]
    pub fn __set_env<A, B>(&mut self, a: A, b: B) -> &mut Build
    where
        A: AsRef<OsStr>,
        B: AsRef<OsStr>,
    {
        self.env
            .push((a.as_ref().to_owned(), b.as_ref().to_owned()));
        self
    }

    /// Run the compiler, generating the file `output`
    ///
    /// This will return a result instead of panicing; see compile() for the complete description.
    pub fn try_compile(&self, output: &str) -> Result<(), Error> {
        let mut output_components = Path::new(output).components();
        match (output_components.next(), output_components.next()) {
            (Some(Component::Normal(_)), None) => {}
            _ => {
                return Err(Error::new(
                    ErrorKind::InvalidArgument,
                    "argument of `compile` must be a single normal path component",
                ));
            }
        }

        let (lib_name, gnu_lib_name) = if output.starts_with("lib") && output.ends_with(".a") {
            (&output[3..output.len() - 2], output.to_owned())
        } else {
            let mut gnu = String::with_capacity(5 + output.len());
            gnu.push_str("lib");
            gnu.push_str(&output);
            gnu.push_str(".a");
            (output, gnu)
        };
        let dst = self.get_out_dir()?;

        let mut objects = Vec::new();
        for file in self.files.iter() {
            let obj = if file.has_root() {
                // If `file` is an absolute path, prefix the `basename`
                // with the `dirname`'s hash to ensure name uniqueness.
                let basename = file
                    .file_name()
                    .ok_or_else(|| Error::new(ErrorKind::InvalidArgument, "file_name() failure"))?
                    .to_string_lossy();
                let dirname = file
                    .parent()
                    .ok_or_else(|| Error::new(ErrorKind::InvalidArgument, "parent() failure"))?
                    .to_string_lossy();
                let mut hasher = hash_map::DefaultHasher::new();
                hasher.write(dirname.to_string().as_bytes());
                dst.join(format!("{:016x}-{}", hasher.finish(), basename))
                    .with_extension("o")
            } else {
                dst.join(file).with_extension("o")
            };
            let obj = if !obj.starts_with(&dst) {
                dst.join(obj.file_name().ok_or_else(|| {
                    Error::new(ErrorKind::IOError, "Getting object file details failed.")
                })?)
            } else {
                obj
            };

            match obj.parent() {
                Some(s) => fs::create_dir_all(s)?,
                None => {
                    return Err(Error::new(
                        ErrorKind::IOError,
                        "Getting object file details failed.",
                    ));
                }
            };

            objects.push(Object::new(file.to_path_buf(), obj));
        }
        self.compile_objects(&objects)?;
        self.assemble(lib_name, &dst.join(gnu_lib_name), &objects)?;

        if self.get_target()?.contains("msvc") {
            let compiler = self.get_base_compiler()?;
            let atlmfc_lib = compiler
                .env()
                .iter()
                .find(|&&(ref var, _)| var.as_os_str() == OsStr::new("LIB"))
                .and_then(|&(_, ref lib_paths)| {
                    env::split_paths(lib_paths).find(|path| {
                        let sub = Path::new("atlmfc/lib");
                        path.ends_with(sub) || path.parent().map_or(false, |p| p.ends_with(sub))
                    })
                });

            if let Some(atlmfc_lib) = atlmfc_lib {
                self.print(&format!(
                    "cargo:rustc-link-search=native={}",
                    atlmfc_lib.display()
                ));
            }
        }

        if self.link_lib_modifiers.is_empty() {
            self.print(&format!("cargo:rustc-link-lib=static={}", lib_name));
        } else {
            let m = self.link_lib_modifiers.join(",");
            self.print(&format!("cargo:rustc-link-lib=static:{}={}", m, lib_name));
        }
        self.print(&format!("cargo:rustc-link-search=native={}", dst.display()));

        // Add specific C++ libraries, if enabled.
        if self.cpp {
            if let Some(stdlib) = self.get_cpp_link_stdlib()? {
                self.print(&format!("cargo:rustc-link-lib={}", stdlib));
            }
        }

        let cudart = match &self.cudart {
            Some(opt) => opt.as_str(), // {none|shared|static}
            None => "none",
        };
        if cudart != "none" {
            if let Some(nvcc) = which(&self.get_compiler().path) {
                // Try to figure out the -L search path. If it fails,
                // it's on user to specify one by passing it through
                // RUSTFLAGS environment variable.
                let mut libtst = false;
                let mut libdir = nvcc;
                libdir.pop(); // remove 'nvcc'
                libdir.push("..");
                let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
                if cfg!(target_os = "linux") {
                    libdir.push("targets");
                    libdir.push(target_arch.to_owned() + "-linux");
                    libdir.push("lib");
                    libtst = true;
                } else if cfg!(target_env = "msvc") {
                    libdir.push("lib");
                    match target_arch.as_str() {
                        "x86_64" => {
                            libdir.push("x64");
                            libtst = true;
                        }
                        "x86" => {
                            libdir.push("Win32");
                            libtst = true;
                        }
                        _ => libtst = false,
                    }
                }
                if libtst && libdir.is_dir() {
                    println!(
                        "cargo:rustc-link-search=native={}",
                        libdir.to_str().unwrap()
                    );
                }

                // And now the -l flag.
                let lib = match cudart {
                    "shared" => "cudart",
                    "static" => "cudart_static",
                    bad => panic!("unsupported cudart option: {}", bad),
                };
                println!("cargo:rustc-link-lib={}", lib);
            }
        }

        Ok(())
    }

    /// Run the compiler, generating the file `output`
    ///
    /// # Library name
    ///
    /// The `output` string argument determines the file name for the compiled
    /// library. The Rust compiler will create an assembly named "lib"+output+".a".
    /// MSVC will create a file named output+".lib".
    ///
    /// The choice of `output` is close to arbitrary, but:
    ///
    /// - must be nonempty,
    /// - must not contain a path separator (`/`),
    /// - must be unique across all `compile` invocations made by the same build
    ///   script.
    ///
    /// If your build script compiles a single source file, the base name of
    /// that source file would usually be reasonable:
    ///
    /// ```no_run
    /// cc::Build::new().file("blobstore.c").compile("blobstore");
    /// ```
    ///
    /// Compiling multiple source files, some people use their crate's name, or
    /// their crate's name + "-cc".
    ///
    /// Otherwise, please use your imagination.
    ///
    /// For backwards compatibility, if `output` starts with "lib" *and* ends
    /// with ".a", a second "lib" prefix and ".a" suffix do not get added on,
    /// but this usage is deprecated; please omit `lib` and `.a` in the argument
    /// that you pass.
    ///
    /// # Panics
    ///
    /// Panics if `output` is not formatted correctly or if one of the underlying
    /// compiler commands fails. It can also panic if it fails reading file names
    /// or creating directories.
    pub fn compile(&self, output: &str) {
        if let Err(e) = self.try_compile(output) {
            fail(&e.message);
        }
    }

    #[cfg(feature = "parallel")]
    fn compile_objects<'me>(&'me self, objs: &[Object]) -> Result<(), Error> {
        use std::sync::atomic::{AtomicBool, Ordering::SeqCst};
        use std::sync::Once;

        // Limit our parallelism globally with a jobserver. Start off by
        // releasing our own token for this process so we can have a bit of an
        // easier to write loop below. If this fails, though, then we're likely
        // on Windows with the main implicit token, so we just have a bit extra
        // parallelism for a bit and don't reacquire later.
        let server = jobserver();
        let reacquire = server.release_raw().is_ok();

        // When compiling objects in parallel we do a few dirty tricks to speed
        // things up:
        //
        // * First is that we use the `jobserver` crate to limit the parallelism
        //   of this build script. The `jobserver` crate will use a jobserver
        //   configured by Cargo for build scripts to ensure that parallelism is
        //   coordinated across C compilations and Rust compilations. Before we
        //   compile anything we make sure to wait until we acquire a token.
        //
        //   Note that this jobserver is cached globally so we only used one per
        //   process and only worry about creating it once.
        //
        // * Next we use a raw `thread::spawn` per thread to actually compile
        //   objects in parallel. We only actually spawn a thread after we've
        //   acquired a token to perform some work
        //
        // * Finally though we want to keep the dependencies of this crate
        //   pretty light, so we avoid using a safe abstraction like `rayon` and
        //   instead rely on some bits of `unsafe` code. We know that this stack
        //   frame persists while everything is compiling so we use all the
        //   stack-allocated objects without cloning/reallocating. We use a
        //   transmute to `State` with a `'static` lifetime to persist
        //   everything we need across the boundary, and the join-on-drop
        //   semantics of `JoinOnDrop` should ensure that our stack frame is
        //   alive while threads are alive.
        //
        // With all that in mind we compile all objects in a loop here, after we
        // acquire the appropriate tokens, Once all objects have been compiled
        // we join on all the threads and propagate the results of compilation.
        //
        // Note that as a slight optimization we try to break out as soon as
        // possible as soon as any compilation fails to ensure that errors get
        // out to the user as fast as possible.
        let error = AtomicBool::new(false);
        let mut threads = Vec::new();
        for obj in objs {
            if error.load(SeqCst) {
                break;
            }
            let token = server.acquire()?;
            let state = State {
                build: self,
                obj,
                error: &error,
            };
            let state = unsafe { std::mem::transmute::<State, State<'static>>(state) };
            let thread = thread::spawn(|| {
                let state: State<'me> = state; // erase the `'static` lifetime
                let result = state.build.compile_object(state.obj);
                if result.is_err() {
                    state.error.store(true, SeqCst);
                }
                drop(token); // make sure our jobserver token is released after the compile
                return result;
            });
            threads.push(JoinOnDrop(Some(thread)));
        }

        for mut thread in threads {
            if let Some(thread) = thread.0.take() {
                thread.join().expect("thread should not panic")?;
            }
        }

        // Reacquire our process's token before we proceed, which we released
        // before entering the loop above.
        if reacquire {
            server.acquire_raw()?;
        }

        return Ok(());

        /// Shared state from the parent thread to the child thread. This
        /// package of pointers is temporarily transmuted to a `'static`
        /// lifetime to cross the thread boundary and then once the thread is
        /// running we erase the `'static` to go back to an anonymous lifetime.
        struct State<'a> {
            build: &'a Build,
            obj: &'a Object,
            error: &'a AtomicBool,
        }

        /// Returns a suitable `jobserver::Client` used to coordinate
        /// parallelism between build scripts.
        fn jobserver() -> &'static jobserver::Client {
            static INIT: Once = Once::new();
            static mut JOBSERVER: Option<jobserver::Client> = None;

            fn _assert_sync<T: Sync>() {}
            _assert_sync::<jobserver::Client>();

            unsafe {
                INIT.call_once(|| {
                    let server = default_jobserver();
                    JOBSERVER = Some(server);
                });
                JOBSERVER.as_ref().unwrap()
            }
        }

        unsafe fn default_jobserver() -> jobserver::Client {
            // Try to use the environmental jobserver which Cargo typically
            // initializes for us...
            if let Some(client) = jobserver::Client::from_env() {
                return client;
            }

            // ... but if that fails for whatever reason select something
            // reasonable and crate a new jobserver. Use `NUM_JOBS` if set (it's
            // configured by Cargo) and otherwise just fall back to a
            // semi-reasonable number. Note that we could use `num_cpus` here
            // but it's an extra dependency that will almost never be used, so
            // it's generally not too worth it.
            let mut parallelism = 4;
            if let Ok(amt) = env::var("NUM_JOBS") {
                if let Ok(amt) = amt.parse() {
                    parallelism = amt;
                }
            }

            // If we create our own jobserver then be sure to reserve one token
            // for ourselves.
            let client = jobserver::Client::new(parallelism).expect("failed to create jobserver");
            client.acquire_raw().expect("failed to acquire initial");
            return client;
        }

        struct JoinOnDrop(Option<thread::JoinHandle<Result<(), Error>>>);

        impl Drop for JoinOnDrop {
            fn drop(&mut self) {
                if let Some(thread) = self.0.take() {
                    drop(thread.join());
                }
            }
        }
    }

    #[cfg(not(feature = "parallel"))]
    fn compile_objects(&self, objs: &[Object]) -> Result<(), Error> {
        for obj in objs {
            self.compile_object(obj)?;
        }
        Ok(())
    }

    fn compile_object(&self, obj: &Object) -> Result<(), Error> {
        let asm_ext = AsmFileExt::from_path(&obj.src);
        let is_asm = asm_ext.is_some();
        let target = self.get_target()?;
        let msvc = target.contains("msvc");
        let compiler = self.try_get_compiler()?;
        let clang = compiler.family == ToolFamily::Clang;

        let (mut cmd, name) = if msvc && asm_ext == Some(AsmFileExt::DotAsm) {
            self.msvc_macro_assembler()?
        } else {
            let mut cmd = compiler.to_command();
            for &(ref a, ref b) in self.env.iter() {
                cmd.env(a, b);
            }
            (
                cmd,
                compiler
                    .path
                    .file_name()
                    .ok_or_else(|| Error::new(ErrorKind::IOError, "Failed to get compiler path."))?
                    .to_string_lossy()
                    .into_owned(),
            )
        };
        let is_arm = target.contains("aarch64") || target.contains("arm");
        command_add_output_file(&mut cmd, &obj.dst, self.cuda, msvc, clang, is_asm, is_arm);
        // armasm and armasm64 don't requrie -c option
        if !msvc || !is_asm || !is_arm {
            cmd.arg("-c");
        }
        if self.cuda && self.cuda_file_count() > 1 {
            cmd.arg("--device-c");
        }
        if is_asm {
            cmd.args(&self.asm_flags);
        }
        if compiler.family == (ToolFamily::Msvc { clang_cl: true }) && !is_asm {
            // #513: For `clang-cl`, separate flags/options from the input file.
            // When cross-compiling macOS -> Windows, this avoids interpreting
            // common `/Users/...` paths as the `/U` flag and triggering
            // `-Wslash-u-filename` warning.
            cmd.arg("--");
        }
        cmd.arg(&obj.src);
        if cfg!(target_os = "macos") {
            self.fix_env_for_apple_os(&mut cmd)?;
        }

        run(&mut cmd, &name)?;
        Ok(())
    }

    /// This will return a result instead of panicing; see expand() for the complete description.
    pub fn try_expand(&self) -> Result<Vec<u8>, Error> {
        let compiler = self.try_get_compiler()?;
        let mut cmd = compiler.to_command();
        for &(ref a, ref b) in self.env.iter() {
            cmd.env(a, b);
        }
        cmd.arg("-E");

        assert!(
            self.files.len() <= 1,
            "Expand may only be called for a single file"
        );

        for file in self.files.iter() {
            cmd.arg(file);
        }

        let name = compiler
            .path
            .file_name()
            .ok_or_else(|| Error::new(ErrorKind::IOError, "Failed to get compiler path."))?
            .to_string_lossy()
            .into_owned();

        Ok(run_output(&mut cmd, &name)?)
    }

    /// Run the compiler, returning the macro-expanded version of the input files.
    ///
    /// This is only relevant for C and C++ files.
    ///
    /// # Panics
    /// Panics if more than one file is present in the config, or if compiler
    /// path has an invalid file name.
    ///
    /// # Example
    /// ```no_run
    /// let out = cc::Build::new().file("src/foo.c").expand();
    /// ```
    pub fn expand(&self) -> Vec<u8> {
        match self.try_expand() {
            Err(e) => fail(&e.message),
            Ok(v) => v,
        }
    }

    /// Get the compiler that's in use for this configuration.
    ///
    /// This function will return a `Tool` which represents the culmination
    /// of this configuration at a snapshot in time. The returned compiler can
    /// be inspected (e.g. the path, arguments, environment) to forward along to
    /// other tools, or the `to_command` method can be used to invoke the
    /// compiler itself.
    ///
    /// This method will take into account all configuration such as debug
    /// information, optimization level, include directories, defines, etc.
    /// Additionally, the compiler binary in use follows the standard
    /// conventions for this path, e.g. looking at the explicitly set compiler,
    /// environment variables (a number of which are inspected here), and then
    /// falling back to the default configuration.
    ///
    /// # Panics
    ///
    /// Panics if an error occurred while determining the architecture.
    pub fn get_compiler(&self) -> Tool {
        match self.try_get_compiler() {
            Ok(tool) => tool,
            Err(e) => fail(&e.message),
        }
    }

    /// Get the compiler that's in use for this configuration.
    ///
    /// This will return a result instead of panicing; see get_compiler() for the complete description.
    pub fn try_get_compiler(&self) -> Result<Tool, Error> {
        let opt_level = self.get_opt_level()?;
        let target = self.get_target()?;

        let mut cmd = self.get_base_compiler()?;
        let envflags = self.envflags(if self.cpp { "CXXFLAGS" } else { "CFLAGS" });

        // Disable default flag generation via `no_default_flags` or environment variable
        let no_defaults = self.no_default_flags || self.getenv("CRATE_CC_NO_DEFAULTS").is_some();

        if !no_defaults {
            self.add_default_flags(&mut cmd, &target, &opt_level)?;
        } else {
            println!("Info: default compiler flags are disabled");
        }

        for arg in envflags {
            cmd.push_cc_arg(arg.into());
        }

        for directory in self.include_directories.iter() {
            cmd.args.push("-I".into());
            cmd.args.push(directory.into());
        }

        // If warnings and/or extra_warnings haven't been explicitly set,
        // then we set them only if the environment doesn't already have
        // CFLAGS/CXXFLAGS, since those variables presumably already contain
        // the desired set of warnings flags.

        if self
            .warnings
            .unwrap_or(if self.has_flags() { false } else { true })
        {
            let wflags = cmd.family.warnings_flags().into();
            cmd.push_cc_arg(wflags);
        }

        if self
            .extra_warnings
            .unwrap_or(if self.has_flags() { false } else { true })
        {
            if let Some(wflags) = cmd.family.extra_warnings_flags() {
                cmd.push_cc_arg(wflags.into());
            }
        }

        for flag in self.flags.iter() {
            cmd.args.push(flag.into());
        }

        for flag in self.flags_supported.iter() {
            if self.is_flag_supported(flag).unwrap_or(false) {
                cmd.push_cc_arg(flag.into());
            }
        }

        for &(ref key, ref value) in self.definitions.iter() {
            if let Some(ref value) = *value {
                cmd.args.push(format!("-D{}={}", key, value).into());
            } else {
                cmd.args.push(format!("-D{}", key).into());
            }
        }

        if self.warnings_into_errors {
            let warnings_to_errors_flag = cmd.family.warnings_to_errors_flag().into();
            cmd.push_cc_arg(warnings_to_errors_flag);
        }

        Ok(cmd)
    }

    fn add_default_flags(
        &self,
        cmd: &mut Tool,
        target: &str,
        opt_level: &str,
    ) -> Result<(), Error> {
        // Non-target flags
        // If the flag is not conditioned on target variable, it belongs here :)
        match cmd.family {
            ToolFamily::Msvc { .. } => {
                cmd.push_cc_arg("-nologo".into());

                let crt_flag = match self.static_crt {
                    Some(true) => "-MT",
                    Some(false) => "-MD",
                    None => {
                        let features = self
                            .getenv("CARGO_CFG_TARGET_FEATURE")
                            .unwrap_or(String::new());
                        if features.contains("crt-static") {
                            "-MT"
                        } else {
                            "-MD"
                        }
                    }
                };
                cmd.push_cc_arg(crt_flag.into());

                match &opt_level[..] {
                    // Msvc uses /O1 to enable all optimizations that minimize code size.
                    "z" | "s" | "1" => cmd.push_opt_unless_duplicate("-O1".into()),
                    // -O3 is a valid value for gcc and clang compilers, but not msvc. Cap to /O2.
                    "2" | "3" => cmd.push_opt_unless_duplicate("-O2".into()),
                    _ => {}
                }
            }
            ToolFamily::Gnu | ToolFamily::Clang => {
                // arm-linux-androideabi-gcc 4.8 shipped with Android NDK does
                // not support '-Oz'
                if opt_level == "z" && cmd.family != ToolFamily::Clang {
                    cmd.push_opt_unless_duplicate("-Os".into());
                } else {
                    cmd.push_opt_unless_duplicate(format!("-O{}", opt_level).into());
                }

                if cmd.family == ToolFamily::Clang && target.contains("android") {
                    // For compatibility with code that doesn't use pre-defined `__ANDROID__` macro.
                    // If compiler used via ndk-build or cmake (officially supported build methods)
                    // this macros is defined.
                    // See https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/build/cmake/android.toolchain.cmake#456
                    // https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/build/core/build-binary.mk#141
                    cmd.push_opt_unless_duplicate("-DANDROID".into());
                }

                if !target.contains("apple-ios") && !target.contains("apple-watchos") {
                    cmd.push_cc_arg("-ffunction-sections".into());
                    cmd.push_cc_arg("-fdata-sections".into());
                }
                // Disable generation of PIC on bare-metal for now: rust-lld doesn't support this yet
                if self.pic.unwrap_or(
                    !target.contains("windows")
                        && !target.contains("-none-")
                        && !target.contains("uefi"),
                ) {
                    cmd.push_cc_arg("-fPIC".into());
                    // PLT only applies if code is compiled with PIC support,
                    // and only for ELF targets.
                    if target.contains("linux") && !self.use_plt.unwrap_or(true) {
                        cmd.push_cc_arg("-fno-plt".into());
                    }
                }
            }
        }

        if self.get_debug() {
            if self.cuda {
                // NVCC debug flag
                cmd.args.push("-G".into());
            }
            let family = cmd.family;
            family.add_debug_flags(cmd, self.get_dwarf_version());
        }

        if self.get_force_frame_pointer() {
            let family = cmd.family;
            family.add_force_frame_pointer(cmd);
        }

        // Target flags
        match cmd.family {
            ToolFamily::Clang => {
                if !(target.contains("android")
                    && android_clang_compiler_uses_target_arg_internally(&cmd.path))
                {
                    if target.contains("darwin") {
                        if let Some(arch) =
                            map_darwin_target_from_rust_to_compiler_architecture(target)
                        {
                            cmd.args
                                .push(format!("--target={}-apple-darwin", arch).into());
                        }
                    } else if target.contains("macabi") {
                        if let Some(arch) =
                            map_darwin_target_from_rust_to_compiler_architecture(target)
                        {
                            cmd.args
                                .push(format!("--target={}-apple-ios-macabi", arch).into());
                        }
                    } else if target.contains("ios-sim") {
                        if let Some(arch) =
                            map_darwin_target_from_rust_to_compiler_architecture(target)
                        {
                            let deployment_target = env::var("IPHONEOS_DEPLOYMENT_TARGET")
                                .unwrap_or_else(|_| "7.0".into());
                            cmd.args.push(
                                format!(
                                    "--target={}-apple-ios{}-simulator",
                                    arch, deployment_target
                                )
                                .into(),
                            );
                        }
                    } else if target.contains("watchos-sim") {
                        if let Some(arch) =
                            map_darwin_target_from_rust_to_compiler_architecture(target)
                        {
                            let deployment_target = env::var("WATCHOS_DEPLOYMENT_TARGET")
                                .unwrap_or_else(|_| "5.0".into());
                            cmd.args.push(
                                format!(
                                    "--target={}-apple-watchos{}-simulator",
                                    arch, deployment_target
                                )
                                .into(),
                            );
                        }
                    } else if target.starts_with("riscv64gc-") {
                        cmd.args.push(
                            format!("--target={}", target.replace("riscv64gc", "riscv64")).into(),
                        );
                    } else if target.starts_with("riscv32gc-") {
                        cmd.args.push(
                            format!("--target={}", target.replace("riscv32gc", "riscv32")).into(),
                        );
                    } else if target.contains("uefi") {
                        if target.contains("x86_64") {
                            cmd.args.push("--target=x86_64-unknown-windows-gnu".into());
                        } else if target.contains("i686") {
                            cmd.args.push("--target=i686-unknown-windows-gnu".into())
                        } else if target.contains("aarch64") {
                            cmd.args.push("--target=aarch64-unknown-windows-gnu".into())
                        }
                    } else {
                        cmd.push_cc_arg(format!("--target={}", target).into());
                    }
                }
            }
            ToolFamily::Msvc { clang_cl } => {
                // This is an undocumented flag from MSVC but helps with making
                // builds more reproducible by avoiding putting timestamps into
                // files.
                cmd.push_cc_arg("-Brepro".into());

                if clang_cl {
                    if target.contains("x86_64") {
                        cmd.push_cc_arg("-m64".into());
                    } else if target.contains("86") {
                        cmd.push_cc_arg("-m32".into());
                        cmd.push_cc_arg("-arch:IA32".into());
                    } else {
                        cmd.push_cc_arg(format!("--target={}", target).into());
                    }
                } else {
                    if target.contains("i586") {
                        cmd.push_cc_arg("-arch:IA32".into());
                    }
                }

                // There is a check in corecrt.h that will generate a
                // compilation error if
                // _ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE is
                // not defined to 1. The check was added in Windows
                // 8 days because only store apps were allowed on ARM.
                // This changed with the release of Windows 10 IoT Core.
                // The check will be going away in future versions of
                // the SDK, but for all released versions of the
                // Windows SDK it is required.
                if target.contains("arm") || target.contains("thumb") {
                    cmd.args
                        .push("-D_ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE=1".into());
                }
            }
            ToolFamily::Gnu => {
                if target.contains("i686") || target.contains("i586") {
                    cmd.args.push("-m32".into());
                } else if target == "x86_64-unknown-linux-gnux32" {
                    cmd.args.push("-mx32".into());
                } else if target.contains("x86_64") || target.contains("powerpc64") {
                    cmd.args.push("-m64".into());
                }

                if target.contains("darwin") {
                    if let Some(arch) = map_darwin_target_from_rust_to_compiler_architecture(target)
                    {
                        cmd.args.push("-arch".into());
                        cmd.args.push(arch.into());
                    }
                }

                if target.contains("-kmc-solid_") {
                    cmd.args.push("-finput-charset=utf-8".into());
                }

                if self.static_flag.is_none() {
                    let features = self
                        .getenv("CARGO_CFG_TARGET_FEATURE")
                        .unwrap_or(String::new());
                    if features.contains("crt-static") {
                        cmd.args.push("-static".into());
                    }
                }

                // armv7 targets get to use armv7 instructions
                if (target.starts_with("armv7") || target.starts_with("thumbv7"))
                    && (target.contains("-linux-") || target.contains("-kmc-solid_"))
                {
                    cmd.args.push("-march=armv7-a".into());

                    if target.ends_with("eabihf") {
                        // lowest common denominator FPU
                        cmd.args.push("-mfpu=vfpv3-d16".into());
                    }
                }

                // (x86 Android doesn't say "eabi")
                if target.contains("-androideabi") && target.contains("v7") {
                    // -march=armv7-a handled above
                    cmd.args.push("-mthumb".into());
                    if !target.contains("neon") {
                        // On android we can guarantee some extra float instructions
                        // (specified in the android spec online)
                        // NEON guarantees even more; see below.
                        cmd.args.push("-mfpu=vfpv3-d16".into());
                    }
                    cmd.args.push("-mfloat-abi=softfp".into());
                }

                if target.contains("neon") {
                    cmd.args.push("-mfpu=neon-vfpv4".into());
                }

                if target.starts_with("armv4t-unknown-linux-") {
                    cmd.args.push("-march=armv4t".into());
                    cmd.args.push("-marm".into());
                    cmd.args.push("-mfloat-abi=soft".into());
                }

                if target.starts_with("armv5te-unknown-linux-") {
                    cmd.args.push("-march=armv5te".into());
                    cmd.args.push("-marm".into());
                    cmd.args.push("-mfloat-abi=soft".into());
                }

                // For us arm == armv6 by default
                if target.starts_with("arm-unknown-linux-") {
                    cmd.args.push("-march=armv6".into());
                    cmd.args.push("-marm".into());
                    if target.ends_with("hf") {
                        cmd.args.push("-mfpu=vfp".into());
                    } else {
                        cmd.args.push("-mfloat-abi=soft".into());
                    }
                }

                // We can guarantee some settings for FRC
                if target.starts_with("arm-frc-") {
                    cmd.args.push("-march=armv7-a".into());
                    cmd.args.push("-mcpu=cortex-a9".into());
                    cmd.args.push("-mfpu=vfpv3".into());
                    cmd.args.push("-mfloat-abi=softfp".into());
                    cmd.args.push("-marm".into());
                }

                // Turn codegen down on i586 to avoid some instructions.
                if target.starts_with("i586-unknown-linux-") {
                    cmd.args.push("-march=pentium".into());
                }

                // Set codegen level for i686 correctly
                if target.starts_with("i686-unknown-linux-") {
                    cmd.args.push("-march=i686".into());
                }

                // Looks like `musl-gcc` makes it hard for `-m32` to make its way
                // all the way to the linker, so we need to actually instruct the
                // linker that we're generating 32-bit executables as well. This'll
                // typically only be used for build scripts which transitively use
                // these flags that try to compile executables.
                if target == "i686-unknown-linux-musl" || target == "i586-unknown-linux-musl" {
                    cmd.args.push("-Wl,-melf_i386".into());
                }

                if target.starts_with("thumb") {
                    cmd.args.push("-mthumb".into());

                    if target.ends_with("eabihf") {
                        cmd.args.push("-mfloat-abi=hard".into())
                    }
                }
                if target.starts_with("thumbv6m") {
                    cmd.args.push("-march=armv6s-m".into());
                }
                if target.starts_with("thumbv7em") {
                    cmd.args.push("-march=armv7e-m".into());

                    if target.ends_with("eabihf") {
                        cmd.args.push("-mfpu=fpv4-sp-d16".into())
                    }
                }
                if target.starts_with("thumbv7m") {
                    cmd.args.push("-march=armv7-m".into());
                }
                if target.starts_with("thumbv8m.base") {
                    cmd.args.push("-march=armv8-m.base".into());
                }
                if target.starts_with("thumbv8m.main") {
                    cmd.args.push("-march=armv8-m.main".into());

                    if target.ends_with("eabihf") {
                        cmd.args.push("-mfpu=fpv5-sp-d16".into())
                    }
                }
                if target.starts_with("armebv7r") | target.starts_with("armv7r") {
                    if target.starts_with("armeb") {
                        cmd.args.push("-mbig-endian".into());
                    } else {
                        cmd.args.push("-mlittle-endian".into());
                    }

                    // ARM mode
                    cmd.args.push("-marm".into());

                    // R Profile
                    cmd.args.push("-march=armv7-r".into());

                    if target.ends_with("eabihf") {
                        // Calling convention
                        cmd.args.push("-mfloat-abi=hard".into());

                        // lowest common denominator FPU
                        // (see Cortex-R4 technical reference manual)
                        cmd.args.push("-mfpu=vfpv3-d16".into())
                    } else {
                        // Calling convention
                        cmd.args.push("-mfloat-abi=soft".into());
                    }
                }
                if target.starts_with("armv7a") {
                    cmd.args.push("-march=armv7-a".into());

                    if target.ends_with("eabihf") {
                        // lowest common denominator FPU
                        cmd.args.push("-mfpu=vfpv3-d16".into());
                    }
                }
                if target.starts_with("riscv32") || target.starts_with("riscv64") {
                    // get the 32i/32imac/32imc/64gc/64imac/... part
                    let mut parts = target.split('-');
                    if let Some(arch) = parts.next() {
                        let arch = &arch[5..];
                        if target.contains("linux") && arch.starts_with("64") {
                            cmd.args.push(("-march=rv64gc").into());
                            cmd.args.push("-mabi=lp64d".into());
                        } else if target.contains("freebsd") && arch.starts_with("64") {
                            cmd.args.push(("-march=rv64gc").into());
                            cmd.args.push("-mabi=lp64d".into());
                        } else if target.contains("openbsd") && arch.starts_with("64") {
                            cmd.args.push(("-march=rv64gc").into());
                            cmd.args.push("-mabi=lp64d".into());
                        } else if target.contains("linux") && arch.starts_with("32") {
                            cmd.args.push(("-march=rv32gc").into());
                            cmd.args.push("-mabi=ilp32d".into());
                        } else if arch.starts_with("64") {
                            cmd.args.push(("-march=rv".to_owned() + arch).into());
                            cmd.args.push("-mabi=lp64".into());
                        } else {
                            cmd.args.push(("-march=rv".to_owned() + arch).into());
                            cmd.args.push("-mabi=ilp32".into());
                        }
                        cmd.args.push("-mcmodel=medany".into());
                    }
                }
            }
        }

        if target.contains("apple-ios") || target.contains("apple-watchos") {
            self.ios_watchos_flags(cmd)?;
        }

        if self.static_flag.unwrap_or(false) {
            cmd.args.push("-static".into());
        }
        if self.shared_flag.unwrap_or(false) {
            cmd.args.push("-shared".into());
        }

        if self.cpp {
            match (self.cpp_set_stdlib.as_ref(), cmd.family) {
                (None, _) => {}
                (Some(stdlib), ToolFamily::Gnu) | (Some(stdlib), ToolFamily::Clang) => {
                    cmd.push_cc_arg(format!("-stdlib=lib{}", stdlib).into());
                }
                _ => {
                    println!(
                        "cargo:warning=cpp_set_stdlib is specified, but the {:?} compiler \
                         does not support this option, ignored",
                        cmd.family
                    );
                }
            }
        }

        Ok(())
    }

    fn has_flags(&self) -> bool {
        let flags_env_var_name = if self.cpp { "CXXFLAGS" } else { "CFLAGS" };
        let flags_env_var_value = self.get_var(flags_env_var_name);
        if let Ok(_) = flags_env_var_value {
            true
        } else {
            false
        }
    }

    fn msvc_macro_assembler(&self) -> Result<(Command, String), Error> {
        let target = self.get_target()?;
        let tool = if target.contains("x86_64") {
            "ml64.exe"
        } else if target.contains("arm") {
            "armasm.exe"
        } else if target.contains("aarch64") {
            "armasm64.exe"
        } else {
            "ml.exe"
        };
        let mut cmd = windows_registry::find(&target, tool).unwrap_or_else(|| self.cmd(tool));
        cmd.arg("-nologo"); // undocumented, yet working with armasm[64]
        for directory in self.include_directories.iter() {
            cmd.arg("-I").arg(directory);
        }
        if target.contains("aarch64") || target.contains("arm") {
            if self.get_debug() {
                cmd.arg("-g");
            }

            println!("cargo:warning=The MSVC ARM assemblers do not support -D flags");
        } else {
            if self.get_debug() {
                cmd.arg("-Zi");
            }

            for &(ref key, ref value) in self.definitions.iter() {
                if let Some(ref value) = *value {
                    cmd.arg(&format!("-D{}={}", key, value));
                } else {
                    cmd.arg(&format!("-D{}", key));
                }
            }
        }

        if target.contains("i686") || target.contains("i586") {
            cmd.arg("-safeseh");
        }
        for flag in self.flags.iter() {
            cmd.arg(flag);
        }

        Ok((cmd, tool.to_string()))
    }

    fn assemble(&self, lib_name: &str, dst: &Path, objs: &[Object]) -> Result<(), Error> {
        // Delete the destination if it exists as we want to
        // create on the first iteration instead of appending.
        let _ = fs::remove_file(&dst);

        // Add objects to the archive in limited-length batches. This helps keep
        // the length of the command line within a reasonable length to avoid
        // blowing system limits on limiting platforms like Windows.
        let objs: Vec<_> = objs
            .iter()
            .map(|o| o.dst.clone())
            .chain(self.objects.clone())
            .collect();
        for chunk in objs.chunks(100) {
            self.assemble_progressive(dst, chunk)?;
        }

        if self.cuda && self.cuda_file_count() > 0 {
            // Link the device-side code and add it to the target library,
            // so that non-CUDA linker can link the final binary.

            let out_dir = self.get_out_dir()?;
            let dlink = out_dir.join(lib_name.to_owned() + "_dlink.o");
            let mut nvcc = self.get_compiler().to_command();
            nvcc.arg("--device-link")
                .arg("-o")
                .arg(dlink.clone())
                .arg(dst);
            run(&mut nvcc, "nvcc")?;
            self.assemble_progressive(dst, &[dlink])?;
        }

        let target = self.get_target()?;
        if target.contains("msvc") {
            // The Rust compiler will look for libfoo.a and foo.lib, but the
            // MSVC linker will also be passed foo.lib, so be sure that both
            // exist for now.

            let lib_dst = dst.with_file_name(format!("{}.lib", lib_name));
            let _ = fs::remove_file(&lib_dst);
            match fs::hard_link(&dst, &lib_dst).or_else(|_| {
                // if hard-link fails, just copy (ignoring the number of bytes written)
                fs::copy(&dst, &lib_dst).map(|_| ())
            }) {
                Ok(_) => (),
                Err(_) => {
                    return Err(Error::new(
                        ErrorKind::IOError,
                        "Could not copy or create a hard-link to the generated lib file.",
                    ));
                }
            };
        } else {
            // Non-msvc targets (those using `ar`) need a separate step to add
            // the symbol table to archives since our construction command of
            // `cq` doesn't add it for us.
            let (mut ar, cmd) = self.get_ar()?;
            run(ar.arg("s").arg(dst), &cmd)?;
        }

        Ok(())
    }

    fn assemble_progressive(&self, dst: &Path, objs: &[PathBuf]) -> Result<(), Error> {
        let target = self.get_target()?;

        if target.contains("msvc") {
            let (mut cmd, program) = self.get_ar()?;
            let mut out = OsString::from("-out:");
            out.push(dst);
            cmd.arg(out).arg("-nologo");
            for flag in self.ar_flags.iter() {
                cmd.arg(flag);
            }
            // If the library file already exists, add the library name
            // as an argument to let lib.exe know we are appending the objs.
            if dst.exists() {
                cmd.arg(dst);
            }
            cmd.args(objs);
            run(&mut cmd, &program)?;
        } else {
            let (mut ar, cmd) = self.get_ar()?;

            // Set an environment variable to tell the OSX archiver to ensure
            // that all dates listed in the archive are zero, improving
            // determinism of builds. AFAIK there's not really official
            // documentation of this but there's a lot of references to it if
            // you search google.
            //
            // You can reproduce this locally on a mac with:
            //
            //      $ touch foo.c
            //      $ cc -c foo.c -o foo.o
            //
            //      # Notice that these two checksums are different
            //      $ ar crus libfoo1.a foo.o && sleep 2 && ar crus libfoo2.a foo.o
            //      $ md5sum libfoo*.a
            //
            //      # Notice that these two checksums are the same
            //      $ export ZERO_AR_DATE=1
            //      $ ar crus libfoo1.a foo.o && sleep 2 && touch foo.o && ar crus libfoo2.a foo.o
            //      $ md5sum libfoo*.a
            //
            // In any case if this doesn't end up getting read, it shouldn't
            // cause that many issues!
            ar.env("ZERO_AR_DATE", "1");
            for flag in self.ar_flags.iter() {
                ar.arg(flag);
            }
            run(ar.arg("cq").arg(dst).args(objs), &cmd)?;
        }

        Ok(())
    }

    fn ios_watchos_flags(&self, cmd: &mut Tool) -> Result<(), Error> {
        enum ArchSpec {
            Device(&'static str),
            Simulator(&'static str),
            Catalyst(&'static str),
        }

        enum Os {
            Ios,
            WatchOs,
        }
        impl Display for Os {
            fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
                match self {
                    Os::Ios => f.write_str("iOS"),
                    Os::WatchOs => f.write_str("WatchOS"),
                }
            }
        }

        let target = self.get_target()?;
        let os = if target.contains("-watchos") {
            Os::WatchOs
        } else {
            Os::Ios
        };

        let arch = target.split('-').nth(0).ok_or_else(|| {
            Error::new(
                ErrorKind::ArchitectureInvalid,
                format!("Unknown architecture for {} target.", os).as_str(),
            )
        })?;

        let is_catalyst = match target.split('-').nth(3) {
            Some(v) => v == "macabi",
            None => false,
        };

        let is_sim = match target.split('-').nth(3) {
            Some(v) => v == "sim",
            None => false,
        };

        let arch = if is_catalyst {
            match arch {
                "arm64e" => ArchSpec::Catalyst("arm64e"),
                "arm64" | "aarch64" => ArchSpec::Catalyst("arm64"),
                "x86_64" => ArchSpec::Catalyst("-m64"),
                _ => {
                    return Err(Error::new(
                        ErrorKind::ArchitectureInvalid,
                        "Unknown architecture for iOS target.",
                    ));
                }
            }
        } else if is_sim {
            match arch {
                "arm64" | "aarch64" => ArchSpec::Simulator("-arch arm64"),
                "x86_64" => ArchSpec::Simulator("-m64"),
                _ => {
                    return Err(Error::new(
                        ErrorKind::ArchitectureInvalid,
                        "Unknown architecture for iOS simulator target.",
                    ));
                }
            }
        } else {
            match arch {
                "arm" | "armv7" | "thumbv7" => ArchSpec::Device("armv7"),
                "armv7k" => ArchSpec::Device("armv7k"),
                "armv7s" | "thumbv7s" => ArchSpec::Device("armv7s"),
                "arm64e" => ArchSpec::Device("arm64e"),
                "arm64" | "aarch64" => ArchSpec::Device("arm64"),
                "arm64_32" => ArchSpec::Device("arm64_32"),
                "i386" | "i686" => ArchSpec::Simulator("-m32"),
                "x86_64" => ArchSpec::Simulator("-m64"),
                _ => {
                    return Err(Error::new(
                        ErrorKind::ArchitectureInvalid,
                        format!("Unknown architecture for {} target.", os).as_str(),
                    ));
                }
            }
        };

        let (sdk_prefix, sim_prefix, min_version) = match os {
            Os::Ios => (
                "iphone",
                "ios-",
                std::env::var("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or_else(|_| "7.0".into()),
            ),
            Os::WatchOs => (
                "watch",
                "watch",
                std::env::var("WATCHOS_DEPLOYMENT_TARGET").unwrap_or_else(|_| "2.0".into()),
            ),
        };

        let sdk = match arch {
            ArchSpec::Device(arch) => {
                cmd.args.push("-arch".into());
                cmd.args.push(arch.into());
                cmd.args
                    .push(format!("-m{}os-version-min={}", sdk_prefix, min_version).into());
                format!("{}os", sdk_prefix)
            }
            ArchSpec::Simulator(arch) => {
                cmd.args.push(arch.into());
                cmd.args
                    .push(format!("-m{}simulator-version-min={}", sim_prefix, min_version).into());
                format!("{}simulator", sdk_prefix)
            }
            ArchSpec::Catalyst(_) => "macosx".to_owned(),
        };

        self.print(&format!("Detecting {} SDK path for {}", os, sdk));
        let sdk_path = if let Some(sdkroot) = env::var_os("SDKROOT") {
            sdkroot
        } else {
            self.apple_sdk_root(sdk.as_str())?
        };

        cmd.args.push("-isysroot".into());
        cmd.args.push(sdk_path);
        cmd.args.push("-fembed-bitcode".into());
        /*
         * TODO we probably ultimately want the -fembed-bitcode-marker flag
         * but can't have it now because of an issue in LLVM:
         * https://github.com/rust-lang/cc-rs/issues/301
         * https://github.com/rust-lang/rust/pull/48896#comment-372192660
         */
        /*
        if self.get_opt_level()? == "0" {
            cmd.args.push("-fembed-bitcode-marker".into());
        }
        */

        Ok(())
    }

    fn cmd<P: AsRef<OsStr>>(&self, prog: P) -> Command {
        let mut cmd = Command::new(prog);
        for &(ref a, ref b) in self.env.iter() {
            cmd.env(a, b);
        }
        cmd
    }

    fn get_base_compiler(&self) -> Result<Tool, Error> {
        if let Some(ref c) = self.compiler {
            return Ok(Tool::new(c.clone()));
        }
        let host = self.get_host()?;
        let target = self.get_target()?;
        let (env, msvc, gnu, traditional, clang) = if self.cpp {
            ("CXX", "cl.exe", "g++", "c++", "clang++")
        } else {
            ("CC", "cl.exe", "gcc", "cc", "clang")
        };

        // On historical Solaris systems, "cc" may have been Sun Studio, which
        // is not flag-compatible with "gcc".  This history casts a long shadow,
        // and many modern illumos distributions today ship GCC as "gcc" without
        // also making it available as "cc".
        let default = if host.contains("solaris") || host.contains("illumos") {
            gnu
        } else {
            traditional
        };

        let cl_exe = windows_registry::find_tool(&target, "cl.exe");

        let tool_opt: Option<Tool> = self
            .env_tool(env)
            .map(|(tool, wrapper, args)| {
                // find the driver mode, if any
                const DRIVER_MODE: &str = "--driver-mode=";
                let driver_mode = args
                    .iter()
                    .find(|a| a.starts_with(DRIVER_MODE))
                    .map(|a| &a[DRIVER_MODE.len()..]);
                // Chop off leading/trailing whitespace to work around
                // semi-buggy build scripts which are shared in
                // makefiles/configure scripts (where spaces are far more
                // lenient)
                let mut t = Tool::with_clang_driver(PathBuf::from(tool.trim()), driver_mode);
                if let Some(cc_wrapper) = wrapper {
                    t.cc_wrapper_path = Some(PathBuf::from(cc_wrapper));
                }
                for arg in args {
                    t.cc_wrapper_args.push(arg.into());
                }
                t
            })
            .or_else(|| {
                if target.contains("emscripten") {
                    let tool = if self.cpp { "em++" } else { "emcc" };
                    // Windows uses bat file so we have to be a bit more specific
                    if cfg!(windows) {
                        let mut t = Tool::new(PathBuf::from("cmd"));
                        t.args.push("/c".into());
                        t.args.push(format!("{}.bat", tool).into());
                        Some(t)
                    } else {
                        Some(Tool::new(PathBuf::from(tool)))
                    }
                } else {
                    None
                }
            })
            .or_else(|| cl_exe.clone());

        let tool = match tool_opt {
            Some(t) => t,
            None => {
                let compiler = if host.contains("windows") && target.contains("windows") {
                    if target.contains("msvc") {
                        msvc.to_string()
                    } else {
                        let cc = if target.contains("llvm") { clang } else { gnu };
                        format!("{}.exe", cc)
                    }
                } else if target.contains("apple-ios") {
                    clang.to_string()
                } else if target.contains("apple-watchos") {
                    clang.to_string()
                } else if target.contains("android") {
                    autodetect_android_compiler(&target, &host, gnu, clang)
                } else if target.contains("cloudabi") {
                    format!("{}-{}", target, traditional)
                } else if target == "wasm32-wasi"
                    || target == "wasm32-unknown-wasi"
                    || target == "wasm32-unknown-unknown"
                {
                    "clang".to_string()
                } else if target.contains("vxworks") {
                    if self.cpp {
                        "wr-c++".to_string()
                    } else {
                        "wr-cc".to_string()
                    }
                } else if target.starts_with("armv7a-kmc-solid_") {
                    format!("arm-kmc-eabi-{}", gnu)
                } else if target.starts_with("aarch64-kmc-solid_") {
                    format!("aarch64-kmc-elf-{}", gnu)
                } else if self.get_host()? != target {
                    let prefix = self.prefix_for_target(&target);
                    match prefix {
                        Some(prefix) => {
                            let cc = if target.contains("llvm") { clang } else { gnu };
                            format!("{}-{}", prefix, cc)
                        }
                        None => default.to_string(),
                    }
                } else {
                    default.to_string()
                };

                let mut t = Tool::new(PathBuf::from(compiler));
                if let Some(cc_wrapper) = Self::rustc_wrapper_fallback() {
                    t.cc_wrapper_path = Some(PathBuf::from(cc_wrapper));
                }
                t
            }
        };

        let mut tool = if self.cuda {
            assert!(
                tool.args.is_empty(),
                "CUDA compilation currently assumes empty pre-existing args"
            );
            let nvcc = match self.get_var("NVCC") {
                Err(_) => "nvcc".into(),
                Ok(nvcc) => nvcc,
            };
            let mut nvcc_tool = Tool::with_features(PathBuf::from(nvcc), None, self.cuda);
            nvcc_tool
                .args
                .push(format!("-ccbin={}", tool.path.display()).into());
            nvcc_tool.family = tool.family;
            nvcc_tool
        } else {
            tool
        };

        // New "standalone" C/C++ cross-compiler executables from recent Android NDK
        // are just shell scripts that call main clang binary (from Android NDK) with
        // proper `--target` argument.
        //
        // For example, armv7a-linux-androideabi16-clang passes
        // `--target=armv7a-linux-androideabi16` to clang.
        //
        // As the shell script calls the main clang binary, the command line limit length
        // on Windows is restricted to around 8k characters instead of around 32k characters.
        // To remove this limit, we call the main clang binary directly and construct the
        // `--target=` ourselves.
        if host.contains("windows") && android_clang_compiler_uses_target_arg_internally(&tool.path)
        {
            if let Some(path) = tool.path.file_name() {
                let file_name = path.to_str().unwrap().to_owned();
                let (target, clang) = file_name.split_at(file_name.rfind("-").unwrap());

                tool.path.set_file_name(clang.trim_start_matches("-"));
                tool.path.set_extension("exe");
                tool.args.push(format!("--target={}", target).into());

                // Additionally, shell scripts for target i686-linux-android versions 16 to 24
                // pass the `mstackrealign` option so we do that here as well.
                if target.contains("i686-linux-android") {
                    let (_, version) = target.split_at(target.rfind("d").unwrap() + 1);
                    if let Ok(version) = version.parse::<u32>() {
                        if version > 15 && version < 25 {
                            tool.args.push("-mstackrealign".into());
                        }
                    }
                }
            };
        }

        // If we found `cl.exe` in our environment, the tool we're returning is
        // an MSVC-like tool, *and* no env vars were set then set env vars for
        // the tool that we're returning.
        //
        // Env vars are needed for things like `link.exe` being put into PATH as
        // well as header include paths sometimes. These paths are automatically
        // included by default but if the `CC` or `CXX` env vars are set these
        // won't be used. This'll ensure that when the env vars are used to
        // configure for invocations like `clang-cl` we still get a "works out
        // of the box" experience.
        if let Some(cl_exe) = cl_exe {
            if tool.family == (ToolFamily::Msvc { clang_cl: true })
                && tool.env.len() == 0
                && target.contains("msvc")
            {
                for &(ref k, ref v) in cl_exe.env.iter() {
                    tool.env.push((k.to_owned(), v.to_owned()));
                }
            }
        }

        Ok(tool)
    }

    fn get_var(&self, var_base: &str) -> Result<String, Error> {
        let target = self.get_target()?;
        let host = self.get_host()?;
        let kind = if host == target { "HOST" } else { "TARGET" };
        let target_u = target.replace("-", "_");
        let res = self
            .getenv(&format!("{}_{}", var_base, target))
            .or_else(|| self.getenv(&format!("{}_{}", var_base, target_u)))
            .or_else(|| self.getenv(&format!("{}_{}", kind, var_base)))
            .or_else(|| self.getenv(var_base));

        match res {
            Some(res) => Ok(res),
            None => Err(Error::new(
                ErrorKind::EnvVarNotFound,
                &format!("Could not find environment variable {}.", var_base),
            )),
        }
    }

    fn envflags(&self, name: &str) -> Vec<String> {
        self.get_var(name)
            .unwrap_or(String::new())
            .split_ascii_whitespace()
            .map(|slice| slice.to_string())
            .collect()
    }

    /// Returns a fallback `cc_compiler_wrapper` by introspecting `RUSTC_WRAPPER`
    fn rustc_wrapper_fallback() -> Option<String> {
        // No explicit CC wrapper was detected, but check if RUSTC_WRAPPER
        // is defined and is a build accelerator that is compatible with
        // C/C++ compilers (e.g. sccache)
        const VALID_WRAPPERS: &[&'static str] = &["sccache", "cachepot"];

        let rustc_wrapper = std::env::var_os("RUSTC_WRAPPER")?;
        let wrapper_path = Path::new(&rustc_wrapper);
        let wrapper_stem = wrapper_path.file_stem()?;

        if VALID_WRAPPERS.contains(&wrapper_stem.to_str()?) {
            Some(rustc_wrapper.to_str()?.to_owned())
        } else {
            None
        }
    }

    /// Returns compiler path, optional modifier name from whitelist, and arguments vec
    fn env_tool(&self, name: &str) -> Option<(String, Option<String>, Vec<String>)> {
        let tool = match self.get_var(name) {
            Ok(tool) => tool,
            Err(_) => return None,
        };

        // If this is an exact path on the filesystem we don't want to do any
        // interpretation at all, just pass it on through. This'll hopefully get
        // us to support spaces-in-paths.
        if Path::new(&tool).exists() {
            return Some((tool, None, Vec::new()));
        }

        // Ok now we want to handle a couple of scenarios. We'll assume from
        // here on out that spaces are splitting separate arguments. Two major
        // features we want to support are:
        //
        //      CC='sccache cc'
        //
        // aka using `sccache` or any other wrapper/caching-like-thing for
        // compilations. We want to know what the actual compiler is still,
        // though, because our `Tool` API support introspection of it to see
        // what compiler is in use.
        //
        // additionally we want to support
        //
        //      CC='cc -flag'
        //
        // where the CC env var is used to also pass default flags to the C
        // compiler.
        //
        // It's true that everything here is a bit of a pain, but apparently if
        // you're not literally make or bash then you get a lot of bug reports.
        let known_wrappers = ["ccache", "distcc", "sccache", "icecc", "cachepot"];

        let mut parts = tool.split_whitespace();
        let maybe_wrapper = match parts.next() {
            Some(s) => s,
            None => return None,
        };

        let file_stem = Path::new(maybe_wrapper)
            .file_stem()
            .unwrap()
            .to_str()
            .unwrap();
        if known_wrappers.contains(&file_stem) {
            if let Some(compiler) = parts.next() {
                return Some((
                    compiler.to_string(),
                    Some(maybe_wrapper.to_string()),
                    parts.map(|s| s.to_string()).collect(),
                ));
            }
        }

        Some((
            maybe_wrapper.to_string(),
            Self::rustc_wrapper_fallback(),
            parts.map(|s| s.to_string()).collect(),
        ))
    }

    /// Returns the C++ standard library:
    /// 1. If [cpp_link_stdlib](cc::Build::cpp_link_stdlib) is set, uses its value.
    /// 2. Else if the `CXXSTDLIB` environment variable is set, uses its value.
    /// 3. Else the default is `libc++` for OS X and BSDs, `libc++_shared` for Android,
    /// `None` for MSVC and `libstdc++` for anything else.
    fn get_cpp_link_stdlib(&self) -> Result<Option<String>, Error> {
        match self.cpp_link_stdlib.clone() {
            Some(s) => Ok(s),
            None => {
                if let Ok(stdlib) = self.get_var("CXXSTDLIB") {
                    if stdlib.is_empty() {
                        Ok(None)
                    } else {
                        Ok(Some(stdlib))
                    }
                } else {
                    let target = self.get_target()?;
                    if target.contains("msvc") {
                        Ok(None)
                    } else if target.contains("apple") {
                        Ok(Some("c++".to_string()))
                    } else if target.contains("freebsd") {
                        Ok(Some("c++".to_string()))
                    } else if target.contains("openbsd") {
                        Ok(Some("c++".to_string()))
                    } else if target.contains("android") {
                        Ok(Some("c++_shared".to_string()))
                    } else {
                        Ok(Some("stdc++".to_string()))
                    }
                }
            }
        }
    }

    fn get_ar(&self) -> Result<(Command, String), Error> {
        if let Some(ref p) = self.archiver {
            let name = p.file_name().and_then(|s| s.to_str()).unwrap_or("ar");
            return Ok((self.cmd(p), name.to_string()));
        }
        if let Ok(p) = self.get_var("AR") {
            return Ok((self.cmd(&p), p));
        }
        let target = self.get_target()?;
        let default_ar = "ar".to_string();
        let program = if target.contains("android") {
            format!("{}-ar", target.replace("armv7", "arm"))
        } else if target.contains("emscripten") {
            // Windows use bat files so we have to be a bit more specific
            if cfg!(windows) {
                let mut cmd = self.cmd("cmd");
                cmd.arg("/c").arg("emar.bat");
                return Ok((cmd, "emar.bat".to_string()));
            }

            "emar".to_string()
        } else if target.contains("msvc") {
            let compiler = self.get_base_compiler()?;
            let mut lib = String::new();
            if compiler.family == (ToolFamily::Msvc { clang_cl: true }) {
                // See if there is 'llvm-lib' next to 'clang-cl'
                // Another possibility could be to see if there is 'clang'
                // next to 'clang-cl' and use 'search_programs()' to locate
                // 'llvm-lib'. This is because 'clang-cl' doesn't support
                // the -print-search-dirs option.
                if let Some(mut cmd) = which(&compiler.path) {
                    cmd.pop();
                    cmd.push("llvm-lib.exe");
                    if let Some(llvm_lib) = which(&cmd) {
                        lib = llvm_lib.to_str().unwrap().to_owned();
                    }
                }
            }
            if lib.is_empty() {
                lib = match windows_registry::find(&target, "lib.exe") {
                    Some(t) => return Ok((t, "lib.exe".to_string())),
                    None => "lib.exe".to_string(),
                }
            }
            lib
        } else if target.contains("illumos") {
            // The default 'ar' on illumos uses a non-standard flags,
            // but the OS comes bundled with a GNU-compatible variant.
            //
            // Use the GNU-variant to match other Unix systems.
            "gar".to_string()
        } else if self.get_host()? != target {
            match self.prefix_for_target(&target) {
                Some(p) => {
                    // GCC uses $target-gcc-ar, whereas binutils uses $target-ar -- try both.
                    // Prefer -ar if it exists, as builds of `-gcc-ar` have been observed to be
                    // outright broken (such as when targetting freebsd with `--disable-lto`
                    // toolchain where the archiver attempts to load the LTO plugin anyway but
                    // fails to find one).
                    let mut ar = default_ar;
                    for &infix in &["", "-gcc"] {
                        let target_ar = format!("{}{}-ar", p, infix);
                        if Command::new(&target_ar).output().is_ok() {
                            ar = target_ar;
                            break;
                        }
                    }
                    ar
                }
                None => default_ar,
            }
        } else {
            default_ar
        };
        Ok((self.cmd(&program), program))
    }

    fn prefix_for_target(&self, target: &str) -> Option<String> {
        // Put aside RUSTC_LINKER's prefix to be used as last resort
        let rustc_linker = self.getenv("RUSTC_LINKER").unwrap_or("".to_string());
        // let linker_prefix = rustc_linker.strip_suffix("-gcc"); // >=1.45.0
        let linker_prefix = if rustc_linker.len() > 4 {
            let (prefix, suffix) = rustc_linker.split_at(rustc_linker.len() - 4);
            if suffix == "-gcc" {
                Some(prefix)
            } else {
                None
            }
        } else {
            None
        };
        // CROSS_COMPILE is of the form: "arm-linux-gnueabi-"
        let cc_env = self.getenv("CROSS_COMPILE");
        let cross_compile = cc_env.as_ref().map(|s| s.trim_end_matches('-').to_owned());
        cross_compile.or(match &target[..] {
            // Note: there is no `aarch64-pc-windows-gnu` target, only `-gnullvm`
            "aarch64-pc-windows-gnullvm" => Some("aarch64-w64-mingw32"),
            "aarch64-uwp-windows-gnu" => Some("aarch64-w64-mingw32"),
            "aarch64-unknown-linux-gnu" => Some("aarch64-linux-gnu"),
            "aarch64-unknown-linux-musl" => Some("aarch64-linux-musl"),
            "aarch64-unknown-netbsd" => Some("aarch64--netbsd"),
            "arm-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
            "armv4t-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
            "armv5te-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
            "armv5te-unknown-linux-musleabi" => Some("arm-linux-gnueabi"),
            "arm-frc-linux-gnueabi" => Some("arm-frc-linux-gnueabi"),
            "arm-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
            "arm-unknown-linux-musleabi" => Some("arm-linux-musleabi"),
            "arm-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
            "arm-unknown-netbsd-eabi" => Some("arm--netbsdelf-eabi"),
            "armv6-unknown-netbsd-eabihf" => Some("armv6--netbsdelf-eabihf"),
            "armv7-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
            "armv7-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
            "armv7-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
            "armv7neon-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
            "armv7neon-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
            "thumbv7-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
            "thumbv7-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
            "thumbv7neon-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
            "thumbv7neon-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
            "armv7-unknown-netbsd-eabihf" => Some("armv7--netbsdelf-eabihf"),
            "hexagon-unknown-linux-musl" => Some("hexagon-linux-musl"),
            "i586-unknown-linux-musl" => Some("musl"),
            "i686-pc-windows-gnu" => Some("i686-w64-mingw32"),
            "i686-uwp-windows-gnu" => Some("i686-w64-mingw32"),
            "i686-unknown-linux-gnu" => self.find_working_gnu_prefix(&[
                "i686-linux-gnu",
                "x86_64-linux-gnu", // transparently support gcc-multilib
            ]), // explicit None if not found, so caller knows to fall back
            "i686-unknown-linux-musl" => Some("musl"),
            "i686-unknown-netbsd" => Some("i486--netbsdelf"),
            "mips-unknown-linux-gnu" => Some("mips-linux-gnu"),
            "mips-unknown-linux-musl" => Some("mips-linux-musl"),
            "mipsel-unknown-linux-gnu" => Some("mipsel-linux-gnu"),
            "mipsel-unknown-linux-musl" => Some("mipsel-linux-musl"),
            "mips64-unknown-linux-gnuabi64" => Some("mips64-linux-gnuabi64"),
            "mips64el-unknown-linux-gnuabi64" => Some("mips64el-linux-gnuabi64"),
            "mipsisa32r6-unknown-linux-gnu" => Some("mipsisa32r6-linux-gnu"),
            "mipsisa32r6el-unknown-linux-gnu" => Some("mipsisa32r6el-linux-gnu"),
            "mipsisa64r6-unknown-linux-gnuabi64" => Some("mipsisa64r6-linux-gnuabi64"),
            "mipsisa64r6el-unknown-linux-gnuabi64" => Some("mipsisa64r6el-linux-gnuabi64"),
            "powerpc-unknown-linux-gnu" => Some("powerpc-linux-gnu"),
            "powerpc-unknown-linux-gnuspe" => Some("powerpc-linux-gnuspe"),
            "powerpc-unknown-netbsd" => Some("powerpc--netbsd"),
            "powerpc64-unknown-linux-gnu" => Some("powerpc-linux-gnu"),
            "powerpc64le-unknown-linux-gnu" => Some("powerpc64le-linux-gnu"),
            "riscv32i-unknown-none-elf" => self.find_working_gnu_prefix(&[
                "riscv32-unknown-elf",
                "riscv64-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv32imac-unknown-none-elf" => self.find_working_gnu_prefix(&[
                "riscv32-unknown-elf",
                "riscv64-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv32imac-unknown-xous-elf" => self.find_working_gnu_prefix(&[
                "riscv32-unknown-elf",
                "riscv64-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv32imc-unknown-none-elf" => self.find_working_gnu_prefix(&[
                "riscv32-unknown-elf",
                "riscv64-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv64gc-unknown-none-elf" => self.find_working_gnu_prefix(&[
                "riscv64-unknown-elf",
                "riscv32-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv64imac-unknown-none-elf" => self.find_working_gnu_prefix(&[
                "riscv64-unknown-elf",
                "riscv32-unknown-elf",
                "riscv-none-embed",
            ]),
            "riscv64gc-unknown-linux-gnu" => Some("riscv64-linux-gnu"),
            "riscv32gc-unknown-linux-gnu" => Some("riscv32-linux-gnu"),
            "riscv64gc-unknown-linux-musl" => Some("riscv64-linux-musl"),
            "riscv32gc-unknown-linux-musl" => Some("riscv32-linux-musl"),
            "s390x-unknown-linux-gnu" => Some("s390x-linux-gnu"),
            "sparc-unknown-linux-gnu" => Some("sparc-linux-gnu"),
            "sparc64-unknown-linux-gnu" => Some("sparc64-linux-gnu"),
            "sparc64-unknown-netbsd" => Some("sparc64--netbsd"),
            "sparcv9-sun-solaris" => Some("sparcv9-sun-solaris"),
            "armv7a-none-eabi" => Some("arm-none-eabi"),
            "armv7a-none-eabihf" => Some("arm-none-eabi"),
            "armebv7r-none-eabi" => Some("arm-none-eabi"),
            "armebv7r-none-eabihf" => Some("arm-none-eabi"),
            "armv7r-none-eabi" => Some("arm-none-eabi"),
            "armv7r-none-eabihf" => Some("arm-none-eabi"),
            "thumbv6m-none-eabi" => Some("arm-none-eabi"),
            "thumbv7em-none-eabi" => Some("arm-none-eabi"),
            "thumbv7em-none-eabihf" => Some("arm-none-eabi"),
            "thumbv7m-none-eabi" => Some("arm-none-eabi"),
            "thumbv8m.base-none-eabi" => Some("arm-none-eabi"),
            "thumbv8m.main-none-eabi" => Some("arm-none-eabi"),
            "thumbv8m.main-none-eabihf" => Some("arm-none-eabi"),
            "x86_64-pc-windows-gnu" => Some("x86_64-w64-mingw32"),
            "x86_64-pc-windows-gnullvm" => Some("x86_64-w64-mingw32"),
            "x86_64-uwp-windows-gnu" => Some("x86_64-w64-mingw32"),
            "x86_64-rumprun-netbsd" => Some("x86_64-rumprun-netbsd"),
            "x86_64-unknown-linux-gnu" => self.find_working_gnu_prefix(&[
                "x86_64-linux-gnu", // rustfmt wrap
            ]), // explicit None if not found, so caller knows to fall back
            "x86_64-unknown-linux-musl" => Some("musl"),
            "x86_64-unknown-netbsd" => Some("x86_64--netbsd"),
            _ => linker_prefix,
        }
        .map(|x| x.to_owned()))
    }

    /// Some platforms have multiple, compatible, canonical prefixes. Look through
    /// each possible prefix for a compiler that exists and return it. The prefixes
    /// should be ordered from most-likely to least-likely.
    fn find_working_gnu_prefix(&self, prefixes: &[&'static str]) -> Option<&'static str> {
        let suffix = if self.cpp { "-g++" } else { "-gcc" };
        let extension = std::env::consts::EXE_SUFFIX;

        // Loop through PATH entries searching for each toolchain. This ensures that we
        // are more likely to discover the toolchain early on, because chances are good
        // that the desired toolchain is in one of the higher-priority paths.
        env::var_os("PATH")
            .as_ref()
            .and_then(|path_entries| {
                env::split_paths(path_entries).find_map(|path_entry| {
                    for prefix in prefixes {
                        let target_compiler = format!("{}{}{}", prefix, suffix, extension);
                        if path_entry.join(&target_compiler).exists() {
                            return Some(prefix);
                        }
                    }
                    None
                })
            })
            .map(|prefix| *prefix)
            .or_else(||
            // If no toolchain was found, provide the first toolchain that was passed in.
            // This toolchain has been shown not to exist, however it will appear in the
            // error that is shown to the user which should make it easier to search for
            // where it should be obtained.
            prefixes.first().map(|prefix| *prefix))
    }

    fn get_target(&self) -> Result<String, Error> {
        match self.target.clone() {
            Some(t) => Ok(t),
            None => Ok(self.getenv_unwrap("TARGET")?),
        }
    }

    fn get_host(&self) -> Result<String, Error> {
        match self.host.clone() {
            Some(h) => Ok(h),
            None => Ok(self.getenv_unwrap("HOST")?),
        }
    }

    fn get_opt_level(&self) -> Result<String, Error> {
        match self.opt_level.as_ref().cloned() {
            Some(ol) => Ok(ol),
            None => Ok(self.getenv_unwrap("OPT_LEVEL")?),
        }
    }

    fn get_debug(&self) -> bool {
        self.debug.unwrap_or_else(|| match self.getenv("DEBUG") {
            Some(s) => s != "false",
            None => false,
        })
    }

    fn get_dwarf_version(&self) -> Option<u32> {
        // Tentatively matches the DWARF version defaults as of rustc 1.62.
        let target = self.get_target().ok()?;
        if target.contains("android")
            || target.contains("apple")
            || target.contains("dragonfly")
            || target.contains("freebsd")
            || target.contains("netbsd")
            || target.contains("openbsd")
            || target.contains("windows-gnu")
        {
            Some(2)
        } else if target.contains("linux") {
            Some(4)
        } else {
            None
        }
    }

    fn get_force_frame_pointer(&self) -> bool {
        self.force_frame_pointer.unwrap_or_else(|| self.get_debug())
    }

    fn get_out_dir(&self) -> Result<PathBuf, Error> {
        match self.out_dir.clone() {
            Some(p) => Ok(p),
            None => Ok(env::var_os("OUT_DIR").map(PathBuf::from).ok_or_else(|| {
                Error::new(
                    ErrorKind::EnvVarNotFound,
                    "Environment variable OUT_DIR not defined.",
                )
            })?),
        }
    }

    fn getenv(&self, v: &str) -> Option<String> {
        // Returns true for environment variables cargo sets for build scripts:
        // https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts
        //
        // This handles more of the vars than we actually use (it tries to check
        // complete-ish set), just to avoid needing maintenance if/when new
        // calls to `getenv`/`getenv_unwrap` are added.
        fn provided_by_cargo(envvar: &str) -> bool {
            match envvar {
                v if v.starts_with("CARGO") || v.starts_with("RUSTC") => true,
                "HOST" | "TARGET" | "RUSTDOC" | "OUT_DIR" | "OPT_LEVEL" | "DEBUG" | "PROFILE"
                | "NUM_JOBS" | "RUSTFLAGS" => true,
                _ => false,
            }
        }
        let mut cache = self.env_cache.lock().unwrap();
        if let Some(val) = cache.get(v) {
            return val.clone();
        }
        if self.emit_rerun_if_env_changed && !provided_by_cargo(v) {
            self.print(&format!("cargo:rerun-if-env-changed={}", v));
        }
        let r = env::var(v).ok();
        self.print(&format!("{} = {:?}", v, r));
        cache.insert(v.to_string(), r.clone());
        r
    }

    fn getenv_unwrap(&self, v: &str) -> Result<String, Error> {
        match self.getenv(v) {
            Some(s) => Ok(s),
            None => Err(Error::new(
                ErrorKind::EnvVarNotFound,
                &format!("Environment variable {} not defined.", v.to_string()),
            )),
        }
    }

    fn print(&self, s: &str) {
        if self.cargo_metadata {
            println!("{}", s);
        }
    }

    fn fix_env_for_apple_os(&self, cmd: &mut Command) -> Result<(), Error> {
        let target = self.get_target()?;
        let host = self.get_host()?;
        if host.contains("apple-darwin") && target.contains("apple-darwin") {
            // If, for example, `cargo` runs during the build of an XCode project, then `SDKROOT` environment variable
            // would represent the current target, and this is the problem for us, if we want to compile something
            // for the host, when host != target.
            // We can not just remove `SDKROOT`, because, again, for example, XCode add to PATH
            // /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
            // and `cc` from this path can not find system include files, like `pthread.h`, if `SDKROOT`
            // is not set
            if let Ok(sdkroot) = env::var("SDKROOT") {
                if !sdkroot.contains("MacOSX") {
                    let macos_sdk = self.apple_sdk_root("macosx")?;
                    cmd.env("SDKROOT", macos_sdk);
                }
            }
            // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
            // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
            // although this is apparently ignored when using the linker at "/usr/bin/ld".
            cmd.env_remove("IPHONEOS_DEPLOYMENT_TARGET");
        }
        Ok(())
    }

    fn apple_sdk_root(&self, sdk: &str) -> Result<OsString, Error> {
        let mut cache = self
            .apple_sdk_root_cache
            .lock()
            .expect("apple_sdk_root_cache lock failed");
        if let Some(ret) = cache.get(sdk) {
            return Ok(ret.clone());
        }

        let sdk_path = run_output(
            self.cmd("xcrun")
                .arg("--show-sdk-path")
                .arg("--sdk")
                .arg(sdk),
            "xcrun",
        )?;

        let sdk_path = match String::from_utf8(sdk_path) {
            Ok(p) => p,
            Err(_) => {
                return Err(Error::new(
                    ErrorKind::IOError,
                    "Unable to determine Apple SDK path.",
                ));
            }
        };
        let ret: OsString = sdk_path.trim().into();
        cache.insert(sdk.into(), ret.clone());
        Ok(ret)
    }

    fn cuda_file_count(&self) -> usize {
        self.files
            .iter()
            .filter(|file| file.extension() == Some(OsStr::new("cu")))
            .count()
    }
}

impl Default for Build {
    fn default() -> Build {
        Build::new()
    }
}

impl Tool {
    fn new(path: PathBuf) -> Self {
        Tool::with_features(path, None, false)
    }

    fn with_clang_driver(path: PathBuf, clang_driver: Option<&str>) -> Self {
        Self::with_features(path, clang_driver, false)
    }

    #[cfg(windows)]
    /// Explicitly set the `ToolFamily`, skipping name-based detection.
    fn with_family(path: PathBuf, family: ToolFamily) -> Self {
        Self {
            path: path,
            cc_wrapper_path: None,
            cc_wrapper_args: Vec::new(),
            args: Vec::new(),
            env: Vec::new(),
            family: family,
            cuda: false,
            removed_args: Vec::new(),
        }
    }

    fn with_features(path: PathBuf, clang_driver: Option<&str>, cuda: bool) -> Self {
        // Try to detect family of the tool from its name, falling back to Gnu.
        let family = if let Some(fname) = path.file_name().and_then(|p| p.to_str()) {
            if fname.contains("clang-cl") {
                ToolFamily::Msvc { clang_cl: true }
            } else if fname.ends_with("cl") || fname == "cl.exe" {
                ToolFamily::Msvc { clang_cl: false }
            } else if fname.contains("clang") {
                match clang_driver {
                    Some("cl") => ToolFamily::Msvc { clang_cl: true },
                    _ => ToolFamily::Clang,
                }
            } else {
                ToolFamily::Gnu
            }
        } else {
            ToolFamily::Gnu
        };

        Tool {
            path: path,
            cc_wrapper_path: None,
            cc_wrapper_args: Vec::new(),
            args: Vec::new(),
            env: Vec::new(),
            family: family,
            cuda: cuda,
            removed_args: Vec::new(),
        }
    }

    /// Add an argument to be stripped from the final command arguments.
    fn remove_arg(&mut self, flag: OsString) {
        self.removed_args.push(flag);
    }

    /// Add a flag, and optionally prepend the NVCC wrapper flag "-Xcompiler".
    ///
    /// Currently this is only used for compiling CUDA sources, since NVCC only
    /// accepts a limited set of GNU-like flags, and the rest must be prefixed
    /// with a "-Xcompiler" flag to get passed to the underlying C++ compiler.
    fn push_cc_arg(&mut self, flag: OsString) {
        if self.cuda {
            self.args.push("-Xcompiler".into());
        }
        self.args.push(flag);
    }

    fn is_duplicate_opt_arg(&self, flag: &OsString) -> bool {
        let flag = flag.to_str().unwrap();
        let mut chars = flag.chars();

        // Only duplicate check compiler flags
        if self.is_like_msvc() {
            if chars.next() != Some('/') {
                return false;
            }
        } else if self.is_like_gnu() || self.is_like_clang() {
            if chars.next() != Some('-') {
                return false;
            }
        }

        // Check for existing optimization flags (-O, /O)
        if chars.next() == Some('O') {
            return self
                .args()
                .iter()
                .any(|ref a| a.to_str().unwrap_or("").chars().nth(1) == Some('O'));
        }

        // TODO Check for existing -m..., -m...=..., /arch:... flags
        return false;
    }

    /// Don't push optimization arg if it conflicts with existing args
    fn push_opt_unless_duplicate(&mut self, flag: OsString) {
        if self.is_duplicate_opt_arg(&flag) {
            println!("Info: Ignoring duplicate arg {:?}", &flag);
        } else {
            self.push_cc_arg(flag);
        }
    }

    /// Converts this compiler into a `Command` that's ready to be run.
    ///
    /// This is useful for when the compiler needs to be executed and the
    /// command returned will already have the initial arguments and environment
    /// variables configured.
    pub fn to_command(&self) -> Command {
        let mut cmd = match self.cc_wrapper_path {
            Some(ref cc_wrapper_path) => {
                let mut cmd = Command::new(&cc_wrapper_path);
                cmd.arg(&self.path);
                cmd
            }
            None => Command::new(&self.path),
        };
        cmd.args(&self.cc_wrapper_args);

        let value = self
            .args
            .iter()
            .filter(|a| !self.removed_args.contains(a))
            .collect::<Vec<_>>();
        cmd.args(&value);

        for &(ref k, ref v) in self.env.iter() {
            cmd.env(k, v);
        }
        cmd
    }

    /// Returns the path for this compiler.
    ///
    /// Note that this may not be a path to a file on the filesystem, e.g. "cc",
    /// but rather something which will be resolved when a process is spawned.
    pub fn path(&self) -> &Path {
        &self.path
    }

    /// Returns the default set of arguments to the compiler needed to produce
    /// executables for the target this compiler generates.
    pub fn args(&self) -> &[OsString] {
        &self.args
    }

    /// Returns the set of environment variables needed for this compiler to
    /// operate.
    ///
    /// This is typically only used for MSVC compilers currently.
    pub fn env(&self) -> &[(OsString, OsString)] {
        &self.env
    }

    /// Returns the compiler command in format of CC environment variable.
    /// Or empty string if CC env was not present
    ///
    /// This is typically used by configure script
    pub fn cc_env(&self) -> OsString {
        match self.cc_wrapper_path {
            Some(ref cc_wrapper_path) => {
                let mut cc_env = cc_wrapper_path.as_os_str().to_owned();
                cc_env.push(" ");
                cc_env.push(self.path.to_path_buf().into_os_string());
                for arg in self.cc_wrapper_args.iter() {
                    cc_env.push(" ");
                    cc_env.push(arg);
                }
                cc_env
            }
            None => OsString::from(""),
        }
    }

    /// Returns the compiler flags in format of CFLAGS environment variable.
    /// Important here - this will not be CFLAGS from env, its internal gcc's flags to use as CFLAGS
    /// This is typically used by configure script
    pub fn cflags_env(&self) -> OsString {
        let mut flags = OsString::new();
        for (i, arg) in self.args.iter().enumerate() {
            if i > 0 {
                flags.push(" ");
            }
            flags.push(arg);
        }
        flags
    }

    /// Whether the tool is GNU Compiler Collection-like.
    pub fn is_like_gnu(&self) -> bool {
        self.family == ToolFamily::Gnu
    }

    /// Whether the tool is Clang-like.
    pub fn is_like_clang(&self) -> bool {
        self.family == ToolFamily::Clang
    }

    /// Whether the tool is MSVC-like.
    pub fn is_like_msvc(&self) -> bool {
        match self.family {
            ToolFamily::Msvc { .. } => true,
            _ => false,
        }
    }
}

fn run(cmd: &mut Command, program: &str) -> Result<(), Error> {
    let (mut child, print) = spawn(cmd, program)?;
    let status = match child.wait() {
        Ok(s) => s,
        Err(_) => {
            return Err(Error::new(
                ErrorKind::ToolExecError,
                &format!(
                    "Failed to wait on spawned child process, command {:?} with args {:?}.",
                    cmd, program
                ),
            ));
        }
    };
    print.join().unwrap();
    println!("{}", status);

    if status.success() {
        Ok(())
    } else {
        Err(Error::new(
            ErrorKind::ToolExecError,
            &format!(
                "Command {:?} with args {:?} did not execute successfully (status code {}).",
                cmd, program, status
            ),
        ))
    }
}

fn run_output(cmd: &mut Command, program: &str) -> Result<Vec<u8>, Error> {
    cmd.stdout(Stdio::piped());
    let (mut child, print) = spawn(cmd, program)?;
    let mut stdout = vec![];
    child
        .stdout
        .take()
        .unwrap()
        .read_to_end(&mut stdout)
        .unwrap();
    let status = match child.wait() {
        Ok(s) => s,
        Err(_) => {
            return Err(Error::new(
                ErrorKind::ToolExecError,
                &format!(
                    "Failed to wait on spawned child process, command {:?} with args {:?}.",
                    cmd, program
                ),
            ));
        }
    };
    print.join().unwrap();
    println!("{}", status);

    if status.success() {
        Ok(stdout)
    } else {
        Err(Error::new(
            ErrorKind::ToolExecError,
            &format!(
                "Command {:?} with args {:?} did not execute successfully (status code {}).",
                cmd, program, status
            ),
        ))
    }
}

fn spawn(cmd: &mut Command, program: &str) -> Result<(Child, JoinHandle<()>), Error> {
    println!("running: {:?}", cmd);

    // Capture the standard error coming from these programs, and write it out
    // with cargo:warning= prefixes. Note that this is a bit wonky to avoid
    // requiring the output to be UTF-8, we instead just ship bytes from one
    // location to another.
    match cmd.stderr(Stdio::piped()).spawn() {
        Ok(mut child) => {
            let stderr = BufReader::new(child.stderr.take().unwrap());
            let print = thread::spawn(move || {
                for line in stderr.split(b'\n').filter_map(|l| l.ok()) {
                    print!("cargo:warning=");
                    std::io::stdout().write_all(&line).unwrap();
                    println!("");
                }
            });
            Ok((child, print))
        }
        Err(ref e) if e.kind() == io::ErrorKind::NotFound => {
            let extra = if cfg!(windows) {
                " (see https://github.com/rust-lang/cc-rs#compile-time-requirements \
                 for help)"
            } else {
                ""
            };
            Err(Error::new(
                ErrorKind::ToolNotFound,
                &format!("Failed to find tool. Is `{}` installed?{}", program, extra),
            ))
        }
        Err(ref e) => Err(Error::new(
            ErrorKind::ToolExecError,
            &format!(
                "Command {:?} with args {:?} failed to start: {:?}",
                cmd, program, e
            ),
        )),
    }
}

fn fail(s: &str) -> ! {
    eprintln!("\n\nerror occurred: {}\n\n", s);
    std::process::exit(1);
}

fn command_add_output_file(
    cmd: &mut Command,
    dst: &Path,
    cuda: bool,
    msvc: bool,
    clang: bool,
    is_asm: bool,
    is_arm: bool,
) {
    if msvc && !clang && !cuda && !(is_asm && is_arm) {
        let mut s = OsString::from("-Fo");
        s.push(&dst);
        cmd.arg(s);
    } else {
        cmd.arg("-o").arg(&dst);
    }
}

// Use by default minimum available API level
// See note about naming here
// https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/docs/BuildSystemMaintainers.md#Clang
static NEW_STANDALONE_ANDROID_COMPILERS: [&str; 4] = [
    "aarch64-linux-android21-clang",
    "armv7a-linux-androideabi16-clang",
    "i686-linux-android16-clang",
    "x86_64-linux-android21-clang",
];

// New "standalone" C/C++ cross-compiler executables from recent Android NDK
// are just shell scripts that call main clang binary (from Android NDK) with
// proper `--target` argument.
//
// For example, armv7a-linux-androideabi16-clang passes
// `--target=armv7a-linux-androideabi16` to clang.
// So to construct proper command line check if
// `--target` argument would be passed or not to clang
fn android_clang_compiler_uses_target_arg_internally(clang_path: &Path) -> bool {
    if let Some(filename) = clang_path.file_name() {
        if let Some(filename_str) = filename.to_str() {
            filename_str.contains("android")
        } else {
            false
        }
    } else {
        false
    }
}

#[test]
fn test_android_clang_compiler_uses_target_arg_internally() {
    for version in 16..21 {
        assert!(android_clang_compiler_uses_target_arg_internally(
            &PathBuf::from(format!("armv7a-linux-androideabi{}-clang", version))
        ));
        assert!(android_clang_compiler_uses_target_arg_internally(
            &PathBuf::from(format!("armv7a-linux-androideabi{}-clang++", version))
        ));
    }
    assert!(!android_clang_compiler_uses_target_arg_internally(
        &PathBuf::from("clang")
    ));
    assert!(!android_clang_compiler_uses_target_arg_internally(
        &PathBuf::from("clang++")
    ));
}

fn autodetect_android_compiler(target: &str, host: &str, gnu: &str, clang: &str) -> String {
    let new_clang_key = match target {
        "aarch64-linux-android" => Some("aarch64"),
        "armv7-linux-androideabi" => Some("armv7a"),
        "i686-linux-android" => Some("i686"),
        "x86_64-linux-android" => Some("x86_64"),
        _ => None,
    };

    let new_clang = new_clang_key
        .map(|key| {
            NEW_STANDALONE_ANDROID_COMPILERS
                .iter()
                .find(|x| x.starts_with(key))
        })
        .unwrap_or(None);

    if let Some(new_clang) = new_clang {
        if Command::new(new_clang).output().is_ok() {
            return (*new_clang).into();
        }
    }

    let target = target
        .replace("armv7neon", "arm")
        .replace("armv7", "arm")
        .replace("thumbv7neon", "arm")
        .replace("thumbv7", "arm");
    let gnu_compiler = format!("{}-{}", target, gnu);
    let clang_compiler = format!("{}-{}", target, clang);

    // On Windows, the Android clang compiler is provided as a `.cmd` file instead
    // of a `.exe` file. `std::process::Command` won't run `.cmd` files unless the
    // `.cmd` is explicitly appended to the command name, so we do that here.
    let clang_compiler_cmd = format!("{}-{}.cmd", target, clang);

    // Check if gnu compiler is present
    // if not, use clang
    if Command::new(&gnu_compiler).output().is_ok() {
        gnu_compiler
    } else if host.contains("windows") && Command::new(&clang_compiler_cmd).output().is_ok() {
        clang_compiler_cmd
    } else {
        clang_compiler
    }
}

// Rust and clang/cc don't agree on how to name the target.
fn map_darwin_target_from_rust_to_compiler_architecture(target: &str) -> Option<&'static str> {
    if target.contains("x86_64") {
        Some("x86_64")
    } else if target.contains("arm64e") {
        Some("arm64e")
    } else if target.contains("aarch64") {
        Some("arm64")
    } else if target.contains("i686") {
        Some("i386")
    } else if target.contains("powerpc") {
        Some("ppc")
    } else if target.contains("powerpc64") {
        Some("ppc64")
    } else {
        None
    }
}

fn which(tool: &Path) -> Option<PathBuf> {
    fn check_exe(exe: &mut PathBuf) -> bool {
        let exe_ext = std::env::consts::EXE_EXTENSION;
        exe.exists() || (!exe_ext.is_empty() && exe.set_extension(exe_ext) && exe.exists())
    }

    // If |tool| is not just one "word," assume it's an actual path...
    if tool.components().count() > 1 {
        let mut exe = PathBuf::from(tool);
        return if check_exe(&mut exe) { Some(exe) } else { None };
    }

    // Loop through PATH entries searching for the |tool|.
    let path_entries = env::var_os("PATH")?;
    env::split_paths(&path_entries).find_map(|path_entry| {
        let mut exe = path_entry.join(tool);
        return if check_exe(&mut exe) { Some(exe) } else { None };
    })
}

#[derive(Clone, Copy, PartialEq)]
enum AsmFileExt {
    /// `.asm` files. On MSVC targets, we assume these should be passed to MASM
    /// (`ml{,64}.exe`).
    DotAsm,
    /// `.s` or `.S` files, which do not have the special handling on MSVC targets.
    DotS,
}

impl AsmFileExt {
    fn from_path(file: &Path) -> Option<Self> {
        if let Some(ext) = file.extension() {
            if let Some(ext) = ext.to_str() {
                let ext = ext.to_lowercase();
                match &*ext {
                    "asm" => return Some(AsmFileExt::DotAsm),
                    "s" => return Some(AsmFileExt::DotS),
                    _ => return None,
                }
            }
        }
        None
    }
}