Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 755 insertions, 0 deletions

diff --git a/mfbt/tests/TestUtf8.cpp b/mfbt/tests/TestUtf8.cpp
new file mode 100644
index 0000000000..b3ff9e9ee8
--- /dev/null
+++ b/mfbt/tests/TestUtf8.cpp
@@ -0,0 +1,755 @@
+/* -*- 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/. */
+
+#define MOZ_PRETEND_NO_JSRUST 1
+
+#include "mozilla/Utf8.h"
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/EnumSet.h"
+#include "mozilla/IntegerRange.h"
+#include "mozilla/Span.h"
+
+using mozilla::ArrayLength;
+using mozilla::AsChars;
+using mozilla::DecodeOneUtf8CodePoint;
+using mozilla::EnumSet;
+using mozilla::IntegerRange;
+using mozilla::IsAscii;
+using mozilla::IsUtf8;
+using mozilla::Span;
+using mozilla::Utf8Unit;
+
+// Disable the C++ 2a warning. See bug #1509926
+#if defined(__clang__) && (__clang_major__ >= 6)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wc++2a-compat"
+#endif
+
+static void TestUtf8Unit() {
+  Utf8Unit c('A');
+  MOZ_RELEASE_ASSERT(c.toChar() == 'A');
+  MOZ_RELEASE_ASSERT(c == Utf8Unit('A'));
+  MOZ_RELEASE_ASSERT(c != Utf8Unit('B'));
+  MOZ_RELEASE_ASSERT(c.toUint8() == 0x41);
+
+  unsigned char asUnsigned = 'A';
+  MOZ_RELEASE_ASSERT(c.toUnsignedChar() == asUnsigned);
+  MOZ_RELEASE_ASSERT(Utf8Unit('B').toUnsignedChar() != asUnsigned);
+
+  Utf8Unit first('@');
+  Utf8Unit second('#');
+
+  MOZ_RELEASE_ASSERT(first != second);
+
+  first = second;
+  MOZ_RELEASE_ASSERT(first == second);
+}
+
+template <typename Char>
+struct ToUtf8Units {
+ public:
+  explicit ToUtf8Units(const Char* aStart, const Char* aEnd)
+      : lead(Utf8Unit(aStart[0])), iter(aStart + 1), end(aEnd) {
+    MOZ_RELEASE_ASSERT(!IsAscii(aStart[0]));
+  }
+
+  const Utf8Unit lead;
+  const Char* iter;
+  const Char* const end;
+};
+
+class AssertIfCalled {
+ public:
+  template <typename... Args>
+  void operator()(Args&&... aArgs) {
+    MOZ_RELEASE_ASSERT(false, "AssertIfCalled instance was called");
+  }
+};
+
+// NOTE: For simplicity in treating |aCharN| identically regardless whether it's
+//       a string literal or a more-generalized array, we require |aCharN| be
+//       null-terminated.
+
+template <typename Char, size_t N>
+static void ExpectValidCodePoint(const Char (&aCharN)[N],
+                                 char32_t aExpectedCodePoint) {
+  MOZ_RELEASE_ASSERT(aCharN[N - 1] == 0,
+                     "array must be null-terminated for |aCharN + N - 1| to "
+                     "compute the value of |aIter| as altered by "
+                     "DecodeOneUtf8CodePoint");
+
+  ToUtf8Units<Char> simpleUnit(aCharN, aCharN + N - 1);
+  auto simple =
+      DecodeOneUtf8CodePoint(simpleUnit.lead, &simpleUnit.iter, simpleUnit.end);
+  MOZ_RELEASE_ASSERT(simple.isSome());
+  MOZ_RELEASE_ASSERT(*simple == aExpectedCodePoint);
+  MOZ_RELEASE_ASSERT(simpleUnit.iter == simpleUnit.end);
+
+  ToUtf8Units<Char> complexUnit(aCharN, aCharN + N - 1);
+  auto complex = DecodeOneUtf8CodePoint(
+      complexUnit.lead, &complexUnit.iter, complexUnit.end, AssertIfCalled(),
+      AssertIfCalled(), AssertIfCalled(), AssertIfCalled(), AssertIfCalled());
+  MOZ_RELEASE_ASSERT(complex.isSome());
+  MOZ_RELEASE_ASSERT(*complex == aExpectedCodePoint);
+  MOZ_RELEASE_ASSERT(complexUnit.iter == complexUnit.end);
+}
+
+enum class InvalidUtf8Reason {
+  BadLeadUnit,
+  NotEnoughUnits,
+  BadTrailingUnit,
+  BadCodePoint,
+  NotShortestForm,
+};
+
+template <typename Char, size_t N>
+static void ExpectInvalidCodePointHelper(const Char (&aCharN)[N],
+                                         InvalidUtf8Reason aExpectedReason,
+                                         uint8_t aExpectedUnitsAvailable,
+                                         uint8_t aExpectedUnitsNeeded,
+                                         char32_t aExpectedBadCodePoint,
+                                         uint8_t aExpectedUnitsObserved) {
+  MOZ_RELEASE_ASSERT(aCharN[N - 1] == 0,
+                     "array must be null-terminated for |aCharN + N - 1| to "
+                     "compute the value of |aIter| as altered by "
+                     "DecodeOneUtf8CodePoint");
+
+  ToUtf8Units<Char> simpleUnit(aCharN, aCharN + N - 1);
+  auto simple =
+      DecodeOneUtf8CodePoint(simpleUnit.lead, &simpleUnit.iter, simpleUnit.end);
+  MOZ_RELEASE_ASSERT(simple.isNothing());
+  MOZ_RELEASE_ASSERT(static_cast<const void*>(simpleUnit.iter) == aCharN);
+
+  EnumSet<InvalidUtf8Reason> reasons;
+  uint8_t unitsAvailable;
+  uint8_t unitsNeeded;
+  char32_t badCodePoint;
+  uint8_t unitsObserved;
+
+  struct OnNotShortestForm {
+    EnumSet<InvalidUtf8Reason>& reasons;
+    char32_t& badCodePoint;
+    uint8_t& unitsObserved;
+
+    void operator()(char32_t aBadCodePoint, uint8_t aUnitsObserved) {
+      reasons += InvalidUtf8Reason::NotShortestForm;
+      badCodePoint = aBadCodePoint;
+      unitsObserved = aUnitsObserved;
+    }
+  };
+
+  ToUtf8Units<Char> complexUnit(aCharN, aCharN + N - 1);
+  auto complex = DecodeOneUtf8CodePoint(
+      complexUnit.lead, &complexUnit.iter, complexUnit.end,
+      [&reasons]() { reasons += InvalidUtf8Reason::BadLeadUnit; },
+      [&reasons, &unitsAvailable, &unitsNeeded](uint8_t aUnitsAvailable,
+                                                uint8_t aUnitsNeeded) {
+        reasons += InvalidUtf8Reason::NotEnoughUnits;
+        unitsAvailable = aUnitsAvailable;
+        unitsNeeded = aUnitsNeeded;
+      },
+      [&reasons, &unitsObserved](uint8_t aUnitsObserved) {
+        reasons += InvalidUtf8Reason::BadTrailingUnit;
+        unitsObserved = aUnitsObserved;
+      },
+      [&reasons, &badCodePoint, &unitsObserved](char32_t aBadCodePoint,
+                                                uint8_t aUnitsObserved) {
+        reasons += InvalidUtf8Reason::BadCodePoint;
+        badCodePoint = aBadCodePoint;
+        unitsObserved = aUnitsObserved;
+      },
+      [&reasons, &badCodePoint, &unitsObserved](char32_t aBadCodePoint,
+                                                uint8_t aUnitsObserved) {
+        reasons += InvalidUtf8Reason::NotShortestForm;
+        badCodePoint = aBadCodePoint;
+        unitsObserved = aUnitsObserved;
+      });
+  MOZ_RELEASE_ASSERT(complex.isNothing());
+  MOZ_RELEASE_ASSERT(static_cast<const void*>(complexUnit.iter) == aCharN);
+
+  bool alreadyIterated = false;
+  for (InvalidUtf8Reason reason : reasons) {
+    MOZ_RELEASE_ASSERT(!alreadyIterated);
+    alreadyIterated = true;
+
+    switch (reason) {
+      case InvalidUtf8Reason::BadLeadUnit:
+        break;
+
+      case InvalidUtf8Reason::NotEnoughUnits:
+        MOZ_RELEASE_ASSERT(unitsAvailable == aExpectedUnitsAvailable);
+        MOZ_RELEASE_ASSERT(unitsNeeded == aExpectedUnitsNeeded);
+        break;
+
+      case InvalidUtf8Reason::BadTrailingUnit:
+        MOZ_RELEASE_ASSERT(unitsObserved == aExpectedUnitsObserved);
+        break;
+
+      case InvalidUtf8Reason::BadCodePoint:
+        MOZ_RELEASE_ASSERT(badCodePoint == aExpectedBadCodePoint);
+        MOZ_RELEASE_ASSERT(unitsObserved == aExpectedUnitsObserved);
+        break;
+
+      case InvalidUtf8Reason::NotShortestForm:
+        MOZ_RELEASE_ASSERT(badCodePoint == aExpectedBadCodePoint);
+        MOZ_RELEASE_ASSERT(unitsObserved == aExpectedUnitsObserved);
+        break;
+    }
+  }
+}
+
+// NOTE: For simplicity in treating |aCharN| identically regardless whether it's
+//       a string literal or a more-generalized array, we require |aCharN| be
+//       null-terminated in all these functions.
+
+template <typename Char, size_t N>
+static void ExpectBadLeadUnit(const Char (&aCharN)[N]) {
+  ExpectInvalidCodePointHelper(aCharN, InvalidUtf8Reason::BadLeadUnit, 0xFF,
+                               0xFF, 0xFFFFFFFF, 0xFF);
+}
+
+template <typename Char, size_t N>
+static void ExpectNotEnoughUnits(const Char (&aCharN)[N],
+                                 uint8_t aExpectedUnitsAvailable,
+                                 uint8_t aExpectedUnitsNeeded) {
+  ExpectInvalidCodePointHelper(aCharN, InvalidUtf8Reason::NotEnoughUnits,
+                               aExpectedUnitsAvailable, aExpectedUnitsNeeded,
+                               0xFFFFFFFF, 0xFF);
+}
+
+template <typename Char, size_t N>
+static void ExpectBadTrailingUnit(const Char (&aCharN)[N],
+                                  uint8_t aExpectedUnitsObserved) {
+  ExpectInvalidCodePointHelper(aCharN, InvalidUtf8Reason::BadTrailingUnit, 0xFF,
+                               0xFF, 0xFFFFFFFF, aExpectedUnitsObserved);
+}
+
+template <typename Char, size_t N>
+static void ExpectNotShortestForm(const Char (&aCharN)[N],
+                                  char32_t aExpectedBadCodePoint,
+                                  uint8_t aExpectedUnitsObserved) {
+  ExpectInvalidCodePointHelper(aCharN, InvalidUtf8Reason::NotShortestForm, 0xFF,
+                               0xFF, aExpectedBadCodePoint,
+                               aExpectedUnitsObserved);
+}
+
+template <typename Char, size_t N>
+static void ExpectBadCodePoint(const Char (&aCharN)[N],
+                               char32_t aExpectedBadCodePoint,
+                               uint8_t aExpectedUnitsObserved) {
+  ExpectInvalidCodePointHelper(aCharN, InvalidUtf8Reason::BadCodePoint, 0xFF,
+                               0xFF, aExpectedBadCodePoint,
+                               aExpectedUnitsObserved);
+}
+
+static void TestIsUtf8() {
+  // Note we include the U+0000 NULL in this one -- and that's fine.
+  static const char asciiBytes[] = u8"How about a nice game of chess?";
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(asciiBytes, ArrayLength(asciiBytes))));
+
+  static const char endNonAsciiBytes[] = u8"Life is like a 🌯";
+  MOZ_RELEASE_ASSERT(
+      IsUtf8(Span(endNonAsciiBytes, ArrayLength(endNonAsciiBytes) - 1)));
+
+  static const unsigned char badLeading[] = {0x80};
+  MOZ_RELEASE_ASSERT(
+      !IsUtf8(AsChars(Span(badLeading, ArrayLength(badLeading)))));
+
+  // Byte-counts
+
+  // 1
+  static const char oneBytes[] = u8"A";  // U+0041 LATIN CAPITAL LETTER A
+  constexpr size_t oneBytesLen = ArrayLength(oneBytes);
+  static_assert(oneBytesLen == 2, "U+0041 plus nul");
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(oneBytes, oneBytesLen)));
+
+  // 2
+  static const char twoBytes[] = u8"؆";  // U+0606 ARABIC-INDIC CUBE ROOT
+  constexpr size_t twoBytesLen = ArrayLength(twoBytes);
+  static_assert(twoBytesLen == 3, "U+0606 in two bytes plus nul");
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(twoBytes, twoBytesLen)));
+
+  ExpectValidCodePoint(twoBytes, 0x0606);
+
+  // 3
+  static const char threeBytes[] = u8"᨞";  // U+1A1E BUGINESE PALLAWA
+  constexpr size_t threeBytesLen = ArrayLength(threeBytes);
+  static_assert(threeBytesLen == 4, "U+1A1E in three bytes plus nul");
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(threeBytes, threeBytesLen)));
+
+  ExpectValidCodePoint(threeBytes, 0x1A1E);
+
+  // 4
+  static const char fourBytes[] =
+      u8"🁡";  // U+1F061 DOMINO TILE HORIZONTAL-06-06
+  constexpr size_t fourBytesLen = ArrayLength(fourBytes);
+  static_assert(fourBytesLen == 5, "U+1F061 in four bytes plus nul");
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(fourBytes, fourBytesLen)));
+
+  ExpectValidCodePoint(fourBytes, 0x1F061);
+
+  // Max code point
+  static const char maxCodePoint[] = u8"􏿿";  // U+10FFFF
+  constexpr size_t maxCodePointLen = ArrayLength(maxCodePoint);
+  static_assert(maxCodePointLen == 5, "U+10FFFF in four bytes plus nul");
+  MOZ_RELEASE_ASSERT(IsUtf8(Span(maxCodePoint, maxCodePointLen)));
+
+  ExpectValidCodePoint(maxCodePoint, 0x10FFFF);
+
+  // One past max code point
+  static const unsigned char onePastMaxCodePoint[] = {0xF4, 0x90, 0x80, 0x80,
+                                                      0x0};
+  constexpr size_t onePastMaxCodePointLen = ArrayLength(onePastMaxCodePoint);
+  MOZ_RELEASE_ASSERT(
+      !IsUtf8(AsChars(Span(onePastMaxCodePoint, onePastMaxCodePointLen))));
+
+  ExpectBadCodePoint(onePastMaxCodePoint, 0x110000, 4);
+
+  // Surrogate-related testing
+
+  // (Note that the various code unit sequences here are null-terminated to
+  // simplify life for ExpectValidCodePoint, which presumes null termination.)
+
+  static const unsigned char justBeforeSurrogates[] = {0xED, 0x9F, 0xBF, 0x0};
+  constexpr size_t justBeforeSurrogatesLen =
+      ArrayLength(justBeforeSurrogates) - 1;
+  MOZ_RELEASE_ASSERT(
+      IsUtf8(AsChars(Span(justBeforeSurrogates, justBeforeSurrogatesLen))));
+
+  ExpectValidCodePoint(justBeforeSurrogates, 0xD7FF);
+
+  static const unsigned char leastSurrogate[] = {0xED, 0xA0, 0x80, 0x0};
+  constexpr size_t leastSurrogateLen = ArrayLength(leastSurrogate) - 1;
+  MOZ_RELEASE_ASSERT(!IsUtf8(AsChars(Span(leastSurrogate, leastSurrogateLen))));
+
+  ExpectBadCodePoint(leastSurrogate, 0xD800, 3);
+
+  static const unsigned char arbitraryHighSurrogate[] = {0xED, 0xA2, 0x87, 0x0};
+  constexpr size_t arbitraryHighSurrogateLen =
+      ArrayLength(arbitraryHighSurrogate) - 1;
+  MOZ_RELEASE_ASSERT(!IsUtf8(
+      AsChars(Span(arbitraryHighSurrogate, arbitraryHighSurrogateLen))));
+
+  ExpectBadCodePoint(arbitraryHighSurrogate, 0xD887, 3);
+
+  static const unsigned char arbitraryLowSurrogate[] = {0xED, 0xB7, 0xAF, 0x0};
+  constexpr size_t arbitraryLowSurrogateLen =
+      ArrayLength(arbitraryLowSurrogate) - 1;
+  MOZ_RELEASE_ASSERT(
+      !IsUtf8(AsChars(Span(arbitraryLowSurrogate, arbitraryLowSurrogateLen))));
+
+  ExpectBadCodePoint(arbitraryLowSurrogate, 0xDDEF, 3);
+
+  static const unsigned char greatestSurrogate[] = {0xED, 0xBF, 0xBF, 0x0};
+  constexpr size_t greatestSurrogateLen = ArrayLength(greatestSurrogate) - 1;
+  MOZ_RELEASE_ASSERT(
+      !IsUtf8(AsChars(Span(greatestSurrogate, greatestSurrogateLen))));
+
+  ExpectBadCodePoint(greatestSurrogate, 0xDFFF, 3);
+
+  static const unsigned char justAfterSurrogates[] = {0xEE, 0x80, 0x80, 0x0};
+  constexpr size_t justAfterSurrogatesLen =
+      ArrayLength(justAfterSurrogates) - 1;
+  MOZ_RELEASE_ASSERT(
+      IsUtf8(AsChars(Span(justAfterSurrogates, justAfterSurrogatesLen))));
+
+  ExpectValidCodePoint(justAfterSurrogates, 0xE000);
+}
+
+static void TestDecodeOneValidUtf8CodePoint() {
+  // NOTE: DecodeOneUtf8CodePoint decodes only *non*-ASCII code points that
+  //       consist of multiple code units, so there are no ASCII tests below.
+
+  // Length two.
+
+  ExpectValidCodePoint(u8"€", 0x80);  // <control>
+  ExpectValidCodePoint(u8"©", 0xA9);   // COPYRIGHT SIGN
+  ExpectValidCodePoint(u8"¶", 0xB6);   // PILCROW SIGN
+  ExpectValidCodePoint(u8"¾", 0xBE);   // VULGAR FRACTION THREE QUARTERS
+  ExpectValidCodePoint(u8"÷", 0xF7);   // DIVISION SIGN
+  ExpectValidCodePoint(u8"ÿ", 0xFF);   // LATIN SMALL LETTER Y WITH DIAERESIS
+  ExpectValidCodePoint(u8"Ā", 0x100);  // LATIN CAPITAL LETTER A WITH MACRON
+  ExpectValidCodePoint(u8"IJ", 0x132);  // LATIN CAPITAL LETTER LIGATURE IJ
+  ExpectValidCodePoint(u8"ͼ", 0x37C);  // GREEK SMALL DOTTED LUNATE SIGMA SYMBOL
+  ExpectValidCodePoint(u8"Ӝ",
+                       0x4DC);  // CYRILLIC CAPITAL LETTER ZHE WITTH DIAERESIS
+  ExpectValidCodePoint(u8"۩", 0x6E9);  // ARABIC PLACE OF SAJDAH
+  ExpectValidCodePoint(u8"߿", 0x7FF);  // <not assigned>
+
+  // Length three.
+
+  ExpectValidCodePoint(u8"ࠀ", 0x800);  // SAMARITAN LETTER ALAF
+  ExpectValidCodePoint(u8"ࡁ", 0x841);  // MANDAIC LETTER AB
+  ExpectValidCodePoint(u8"ࣿ", 0x8FF);   // ARABIC MARK SIDEWAYS NOON GHUNNA
+  ExpectValidCodePoint(u8"ஆ", 0xB86);  // TAMIL LETTER AA
+  ExpectValidCodePoint(u8"༃",
+                       0xF03);  // TIBETAN MARK GTER YIG MGO -UM GTER TSHEG MA
+  ExpectValidCodePoint(
+      u8"࿉",
+      0xFC9);  // TIBETAN SYMBOL NOR BU (but on my system it really looks like
+               // SOFT-SERVE ICE CREAM FROM ABOVE THE PLANE if you ask me)
+  ExpectValidCodePoint(u8"ဪ", 0x102A);           // MYANMAR LETTER AU
+  ExpectValidCodePoint(u8"ᚏ", 0x168F);           // OGHAM LETTER RUIS
+  ExpectValidCodePoint("\xE2\x80\xA8", 0x2028);  // (the hated) LINE SEPARATOR
+  ExpectValidCodePoint("\xE2\x80\xA9",
+                       0x2029);           // (the hated) PARAGRAPH SEPARATOR
+  ExpectValidCodePoint(u8"☬", 0x262C);    // ADI SHAKTI
+  ExpectValidCodePoint(u8"㊮", 0x32AE);   // CIRCLED IDEOGRAPH RESOURCE
+  ExpectValidCodePoint(u8"㏖", 0x33D6);   // SQUARE MOL
+  ExpectValidCodePoint(u8"ꔄ", 0xA504);    // VAI SYLLABLE WEEN
+  ExpectValidCodePoint(u8"ퟕ", 0xD7D5);    // HANGUL JONGSEONG RIEUL-SSANGKIYEOK
+  ExpectValidCodePoint(u8"퟿", 0xD7FF);  // <not assigned>
+  ExpectValidCodePoint(u8"", 0xE000);  // <Private Use>
+  ExpectValidCodePoint(u8"鱗", 0xF9F2);   // CJK COMPATIBILITY IDEOGRAPH-F9F
+  ExpectValidCodePoint(
+      u8"﷽", 0xFDFD);  // ARABIC LIGATURE BISMILLAH AR-RAHMAN AR-RAHHHEEEEM
+  ExpectValidCodePoint(u8"￿", 0xFFFF);  // <not assigned>
+
+  // Length four.
+  ExpectValidCodePoint(u8"𐀀", 0x10000);      // LINEAR B SYLLABLE B008 A
+  ExpectValidCodePoint(u8"𔑀", 0x14440);      // ANATOLIAN HIEROGLYPH A058
+  ExpectValidCodePoint(u8"𝛗", 0x1D6D7);      // MATHEMATICAL BOLD SMALL PHI
+  ExpectValidCodePoint(u8"💩", 0x1F4A9);     // PILE OF POO
+  ExpectValidCodePoint(u8"🔫", 0x1F52B);     // PISTOL
+  ExpectValidCodePoint(u8"🥌", 0x1F94C);     // CURLING STONE
+  ExpectValidCodePoint(u8"🥏", 0x1F94F);     // FLYING DISC
+  ExpectValidCodePoint(u8"𠍆", 0x20346);     // CJK UNIFIED IDEOGRAPH-20346
+  ExpectValidCodePoint(u8"𡠺", 0x2183A);     // CJK UNIFIED IDEOGRAPH-2183A
+  ExpectValidCodePoint(u8"񁟶", 0x417F6);   // <not assigned>
+  ExpectValidCodePoint(u8"񾠶", 0x7E836);   // <not assigned>
+  ExpectValidCodePoint(u8"󾽧", 0xFEF67);   // <Plane 15 Private Use>
+  ExpectValidCodePoint(u8"􏿿", 0x10FFFF);  //
+}
+
+static void TestDecodeBadLeadUnit() {
+  // These tests are actually exhaustive.
+
+  unsigned char badLead[] = {'\0', '\0'};
+
+  for (uint8_t lead : IntegerRange(0b1000'0000, 0b1100'0000)) {
+    badLead[0] = lead;
+    ExpectBadLeadUnit(badLead);
+  }
+
+  {
+    uint8_t lead = 0b1111'1000;
+    do {
+      badLead[0] = lead;
+      ExpectBadLeadUnit(badLead);
+      if (lead == 0b1111'1111) {
+        break;
+      }
+
+      lead++;
+    } while (true);
+  }
+}
+
+static void TestTooFewOrBadTrailingUnits() {
+  // Lead unit indicates a two-byte code point.
+
+  char truncatedTwo[] = {'\0', '\0'};
+  char badTrailTwo[] = {'\0', '\0', '\0'};
+
+  for (uint8_t lead : IntegerRange(0b1100'0000, 0b1110'0000)) {
+    truncatedTwo[0] = lead;
+    ExpectNotEnoughUnits(truncatedTwo, 1, 2);
+
+    badTrailTwo[0] = lead;
+    for (uint8_t trail : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailTwo[1] = trail;
+      ExpectBadTrailingUnit(badTrailTwo, 2);
+    }
+
+    for (uint8_t trail : IntegerRange(0b1100'0000, 0b1111'1111)) {
+      badTrailTwo[1] = trail;
+      ExpectBadTrailingUnit(badTrailTwo, 2);
+    }
+  }
+
+  // Lead unit indicates a three-byte code point.
+
+  char truncatedThreeOne[] = {'\0', '\0'};
+  char truncatedThreeTwo[] = {'\0', '\0', '\0'};
+  unsigned char badTrailThree[] = {'\0', '\0', '\0', '\0'};
+
+  for (uint8_t lead : IntegerRange(0b1110'0000, 0b1111'0000)) {
+    truncatedThreeOne[0] = lead;
+    ExpectNotEnoughUnits(truncatedThreeOne, 1, 3);
+
+    truncatedThreeTwo[0] = lead;
+    ExpectNotEnoughUnits(truncatedThreeTwo, 2, 3);
+
+    badTrailThree[0] = lead;
+    badTrailThree[2] = 0b1011'1111;  // make valid to test overreads
+    for (uint8_t mid : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailThree[1] = mid;
+      ExpectBadTrailingUnit(badTrailThree, 2);
+    }
+    {
+      uint8_t mid = 0b1100'0000;
+      do {
+        badTrailThree[1] = mid;
+        ExpectBadTrailingUnit(badTrailThree, 2);
+        if (mid == 0b1111'1111) {
+          break;
+        }
+
+        mid++;
+      } while (true);
+    }
+
+    badTrailThree[1] = 0b1011'1111;
+    for (uint8_t last : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailThree[2] = last;
+      ExpectBadTrailingUnit(badTrailThree, 3);
+    }
+    {
+      uint8_t last = 0b1100'0000;
+      do {
+        badTrailThree[2] = last;
+        ExpectBadTrailingUnit(badTrailThree, 3);
+        if (last == 0b1111'1111) {
+          break;
+        }
+
+        last++;
+      } while (true);
+    }
+  }
+
+  // Lead unit indicates a four-byte code point.
+
+  char truncatedFourOne[] = {'\0', '\0'};
+  char truncatedFourTwo[] = {'\0', '\0', '\0'};
+  char truncatedFourThree[] = {'\0', '\0', '\0', '\0'};
+
+  unsigned char badTrailFour[] = {'\0', '\0', '\0', '\0', '\0'};
+
+  for (uint8_t lead : IntegerRange(0b1111'0000, 0b1111'1000)) {
+    truncatedFourOne[0] = lead;
+    ExpectNotEnoughUnits(truncatedFourOne, 1, 4);
+
+    truncatedFourTwo[0] = lead;
+    ExpectNotEnoughUnits(truncatedFourTwo, 2, 4);
+
+    truncatedFourThree[0] = lead;
+    ExpectNotEnoughUnits(truncatedFourThree, 3, 4);
+
+    badTrailFour[0] = lead;
+    badTrailFour[2] = badTrailFour[3] = 0b1011'1111;  // test for overreads
+    for (uint8_t second : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailFour[1] = second;
+      ExpectBadTrailingUnit(badTrailFour, 2);
+    }
+    {
+      uint8_t second = 0b1100'0000;
+      do {
+        badTrailFour[1] = second;
+        ExpectBadTrailingUnit(badTrailFour, 2);
+        if (second == 0b1111'1111) {
+          break;
+        }
+
+        second++;
+      } while (true);
+    }
+
+    badTrailFour[1] = badTrailFour[3] = 0b1011'1111;  // test for overreads
+    for (uint8_t third : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailFour[2] = third;
+      ExpectBadTrailingUnit(badTrailFour, 3);
+    }
+    {
+      uint8_t third = 0b1100'0000;
+      do {
+        badTrailFour[2] = third;
+        ExpectBadTrailingUnit(badTrailFour, 3);
+        if (third == 0b1111'1111) {
+          break;
+        }
+
+        third++;
+      } while (true);
+    }
+
+    badTrailFour[2] = 0b1011'1111;
+    for (uint8_t fourth : IntegerRange(0b0000'0000, 0b1000'0000)) {
+      badTrailFour[3] = fourth;
+      ExpectBadTrailingUnit(badTrailFour, 4);
+    }
+    {
+      uint8_t fourth = 0b1100'0000;
+      do {
+        badTrailFour[3] = fourth;
+        ExpectBadTrailingUnit(badTrailFour, 4);
+        if (fourth == 0b1111'1111) {
+          break;
+        }
+
+        fourth++;
+      } while (true);
+    }
+  }
+}
+
+static void TestBadSurrogate() {
+  // These tests are actually exhaustive.
+
+  ExpectValidCodePoint("\xED\x9F\xBF", 0xD7FF);  // last before surrogates
+  ExpectValidCodePoint("\xEE\x80\x80", 0xE000);  // first after surrogates
+
+  // First invalid surrogate encoding is { 0xED, 0xA0, 0x80 }.  Last invalid
+  // surrogate encoding is { 0xED, 0xBF, 0xBF }.
+
+  char badSurrogate[] = {'\xED', '\0', '\0', '\0'};
+
+  for (char32_t c = 0xD800; c < 0xE000; c++) {
+    badSurrogate[1] = 0b1000'0000 ^ ((c & 0b1111'1100'0000) >> 6);
+    badSurrogate[2] = 0b1000'0000 ^ ((c & 0b0000'0011'1111));
+
+    ExpectBadCodePoint(badSurrogate, c, 3);
+  }
+}
+
+static void TestBadTooBig() {
+  // These tests are actually exhaustive.
+
+  ExpectValidCodePoint("\xF4\x8F\xBF\xBF", 0x10'FFFF);  // last code point
+
+  // Four-byte code points are
+  //
+  //   0b1111'0xxx 0b10xx'xxxx 0b10xx'xxxx 0b10xx'xxxx
+  //
+  // with 3 + 6 + 6 + 6 == 21 unconstrained bytes, so the structurally
+  // representable limit (exclusive) is 2**21 - 1 == 2097152.
+
+  char tooLargeCodePoint[] = {'\0', '\0', '\0', '\0', '\0'};
+
+  for (char32_t c = 0x11'0000; c < (1 << 21); c++) {
+    tooLargeCodePoint[0] =
+        0b1111'0000 ^ ((c & 0b1'1100'0000'0000'0000'0000) >> 18);
+    tooLargeCodePoint[1] =
+        0b1000'0000 ^ ((c & 0b0'0011'1111'0000'0000'0000) >> 12);
+    tooLargeCodePoint[2] =
+        0b1000'0000 ^ ((c & 0b0'0000'0000'1111'1100'0000) >> 6);
+    tooLargeCodePoint[3] = 0b1000'0000 ^ ((c & 0b0'0000'0000'0000'0011'1111));
+
+    ExpectBadCodePoint(tooLargeCodePoint, c, 4);
+  }
+}
+
+static void TestBadCodePoint() {
+  TestBadSurrogate();
+  TestBadTooBig();
+}
+
+static void TestNotShortestForm() {
+  {
+    // One-byte in two-byte.
+
+    char oneInTwo[] = {'\0', '\0', '\0'};
+
+    for (char32_t c = '\0'; c < 0x80; c++) {
+      oneInTwo[0] = 0b1100'0000 ^ ((c & 0b0111'1100'0000) >> 6);
+      oneInTwo[1] = 0b1000'0000 ^ ((c & 0b0000'0011'1111));
+
+      ExpectNotShortestForm(oneInTwo, c, 2);
+    }
+
+    // One-byte in three-byte.
+
+    char oneInThree[] = {'\0', '\0', '\0', '\0'};
+
+    for (char32_t c = '\0'; c < 0x80; c++) {
+      oneInThree[0] = 0b1110'0000 ^ ((c & 0b1111'0000'0000'0000) >> 12);
+      oneInThree[1] = 0b1000'0000 ^ ((c & 0b0000'1111'1100'0000) >> 6);
+      oneInThree[2] = 0b1000'0000 ^ ((c & 0b0000'0000'0011'1111));
+
+      ExpectNotShortestForm(oneInThree, c, 3);
+    }
+
+    // One-byte in four-byte.
+
+    char oneInFour[] = {'\0', '\0', '\0', '\0', '\0'};
+
+    for (char32_t c = '\0'; c < 0x80; c++) {
+      oneInFour[0] = 0b1111'0000 ^ ((c & 0b1'1100'0000'0000'0000'0000) >> 18);
+      oneInFour[1] = 0b1000'0000 ^ ((c & 0b0'0011'1111'0000'0000'0000) >> 12);
+      oneInFour[2] = 0b1000'0000 ^ ((c & 0b0'0000'0000'1111'1100'0000) >> 6);
+      oneInFour[3] = 0b1000'0000 ^ ((c & 0b0'0000'0000'0000'0011'1111));
+
+      ExpectNotShortestForm(oneInFour, c, 4);
+    }
+  }
+
+  {
+    // Two-byte in three-byte.
+
+    char twoInThree[] = {'\0', '\0', '\0', '\0'};
+
+    for (char32_t c = 0x80; c < 0x800; c++) {
+      twoInThree[0] = 0b1110'0000 ^ ((c & 0b1111'0000'0000'0000) >> 12);
+      twoInThree[1] = 0b1000'0000 ^ ((c & 0b0000'1111'1100'0000) >> 6);
+      twoInThree[2] = 0b1000'0000 ^ ((c & 0b0000'0000'0011'1111));
+
+      ExpectNotShortestForm(twoInThree, c, 3);
+    }
+
+    // Two-byte in four-byte.
+
+    char twoInFour[] = {'\0', '\0', '\0', '\0', '\0'};
+
+    for (char32_t c = 0x80; c < 0x800; c++) {
+      twoInFour[0] = 0b1111'0000 ^ ((c & 0b1'1100'0000'0000'0000'0000) >> 18);
+      twoInFour[1] = 0b1000'0000 ^ ((c & 0b0'0011'1111'0000'0000'0000) >> 12);
+      twoInFour[2] = 0b1000'0000 ^ ((c & 0b0'0000'0000'1111'1100'0000) >> 6);
+      twoInFour[3] = 0b1000'0000 ^ ((c & 0b0'0000'0000'0000'0011'1111));
+
+      ExpectNotShortestForm(twoInFour, c, 4);
+    }
+  }
+
+  {
+    // Three-byte in four-byte.
+
+    char threeInFour[] = {'\0', '\0', '\0', '\0', '\0'};
+
+    for (char32_t c = 0x800; c < 0x1'0000; c++) {
+      threeInFour[0] = 0b1111'0000 ^ ((c & 0b1'1100'0000'0000'0000'0000) >> 18);
+      threeInFour[1] = 0b1000'0000 ^ ((c & 0b0'0011'1111'0000'0000'0000) >> 12);
+      threeInFour[2] = 0b1000'0000 ^ ((c & 0b0'0000'0000'1111'1100'0000) >> 6);
+      threeInFour[3] = 0b1000'0000 ^ ((c & 0b0'0000'0000'0000'0011'1111));
+
+      ExpectNotShortestForm(threeInFour, c, 4);
+    }
+  }
+}
+
+static void TestDecodeOneInvalidUtf8CodePoint() {
+  TestDecodeBadLeadUnit();
+  TestTooFewOrBadTrailingUnits();
+  TestBadCodePoint();
+  TestNotShortestForm();
+}
+
+static void TestDecodeOneUtf8CodePoint() {
+  TestDecodeOneValidUtf8CodePoint();
+  TestDecodeOneInvalidUtf8CodePoint();
+}
+
+int main() {
+  TestUtf8Unit();
+  TestIsUtf8();
+  TestDecodeOneUtf8CodePoint();
+  return 0;
+}
+
+#if defined(__clang__) && (__clang_major__ >= 6)
+#  pragma clang diagnostic pop
+#endif