1 files changed, 97 insertions, 0 deletions
diff --git a/mfbt/MacroArgs.h b/mfbt/MacroArgs.h
new file mode 100644
index 0000000000..9afaaef945
--- /dev/null
+++ b/mfbt/MacroArgs.h
@@ -0,0 +1,97 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Implements various macros meant to ease the use of variadic macros.
+ */
+
+#ifndef mozilla_MacroArgs_h
+#define mozilla_MacroArgs_h
+
+// Concatenates pre-processor tokens in a way that can be used with __LINE__.
+#define MOZ_CONCAT2(x, y) x##y
+#define MOZ_CONCAT(x, y) MOZ_CONCAT2(x, y)
+
+/*
+ * MOZ_ARG_COUNT(...) counts the number of variadic arguments.
+ * You must pass in between 0 and 50 (inclusive) variadic arguments.
+ * For example:
+ *
+ *   MOZ_ARG_COUNT() expands to 0
+ *   MOZ_ARG_COUNT(a) expands to 1
+ *   MOZ_ARG_COUNT(a, b) expands to 2
+ *
+ * Implementation notes:
+ * The `##__VA_ARGS__` form is a GCC extension that removes the comma if
+ * __VA_ARGS__ is empty. It is supported by Clang too. MSVC ignores ##,
+ * and its default behavior is already to strip the comma when __VA_ARGS__
+ * is empty.
+ *
+ * So MOZ_MACROARGS_ARG_COUNT_HELPER() expands to
+ *   (_, 50, 49, ...)
+ * MOZ_MACROARGS_ARG_COUNT_HELPER(a) expands to
+ *   (_, a, 50, 49, ...)
+ * etc.
+ */
+#define MOZ_ARG_COUNT(...) \
+  MOZ_MACROARGS_ARG_COUNT_HELPER2(MOZ_MACROARGS_ARG_COUNT_HELPER(__VA_ARGS__))
+
+#define MOZ_MACROARGS_ARG_COUNT_HELPER(...)                                    \
+  (_, ##__VA_ARGS__, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37,   \
+   36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, \
+   17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
+#define MOZ_MACROARGS_ARG_COUNT_HELPER2(aArgs) \
+  MOZ_MACROARGS_ARG_COUNT_HELPER3 aArgs
+
+#define MOZ_MACROARGS_ARG_COUNT_HELPER3(                                       \
+    a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, \
+    a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, \
+    a32, a33, a34, a35, a36, a37, a38, a39, a40, a41, a42, a43, a44, a45, a46, \
+    a47, a48, a49, a50, a51, ...)                                              \
+  a51
+
+/*
+ * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic
+ * arguments and prefixes it with |aPrefix|. For example:
+ *
+ *   MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2
+ *   MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3
+ *   MOZ_PASTE_PREFIX_AND_ARG_COUNT(A) expands to A0
+ *   MOZ_PASTE_PREFIX_AND_ARG_COUNT() expands to 0, but MSVC warns there
+ *   aren't enough arguments given.
+ *
+ * You must pass in between 0 and 50 (inclusive) variadic arguments, past
+ * |aPrefix|.
+ */
+#define MOZ_PASTE_PREFIX_AND_ARG_COUNT_GLUE(a, b) a b
+#define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \
+  MOZ_PASTE_PREFIX_AND_ARG_COUNT_GLUE(MOZ_CONCAT,    \
+                                      (aPrefix, MOZ_ARG_COUNT(__VA_ARGS__)))
+
+/*
+ * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N|
+ * arguments. For example:
+ *
+ *   MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d
+ */
+#define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__
+#define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__
+
+/*
+ * MOZ_ARG_N expands to its |N|th argument.
+ */
+#define MOZ_ARG_1(a1, ...) a1
+#define MOZ_ARG_2(a1, a2, ...) a2
+#define MOZ_ARG_3(a1, a2, a3, ...) a3
+#define MOZ_ARG_4(a1, a2, a3, a4, ...) a4
+#define MOZ_ARG_5(a1, a2, a3, a4, a5, ...) a5
+#define MOZ_ARG_6(a1, a2, a3, a4, a5, a6, ...) a6
+#define MOZ_ARG_7(a1, a2, a3, a4, a5, a6, a7, ...) a7
+#define MOZ_ARG_8(a1, a2, a3, a4, a5, a6, a7, a8, ...) a8
+#define MOZ_ARG_9(a1, a2, a3, a4, a5, a6, a7, a8, a9, ...) a9
+
+#endif /* mozilla_MacroArgs_h */