Upstream ScriptRunIterator for segmenting text runs by script

Source/platform/fonts/ScriptRunIteratorTest.cpp

Index: Source/platform/fonts/ScriptRunIteratorTest.cpp
diff --git a/Source/platform/fonts/ScriptRunIteratorTest.cpp b/Source/platform/fonts/ScriptRunIteratorTest.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..624ad0b5809c23868fa36ee9cdb2c9800e5627d7
--- /dev/null
+++ b/Source/platform/fonts/ScriptRunIteratorTest.cpp
@@ -0,0 +1,786 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "config.h"
+#include "platform/fonts/ScriptRunIterator.h"
+
+#include "platform/Logging.h"
+#include "wtf/Assertions.h"
+#include "wtf/Threading.h"
+#include "wtf/text/WTFString.h"
+
+#include <gtest/gtest.h>
+#include <string>
+#include <vector>
+
+namespace blink {
+
+struct TestRun {
+    std::string text;
+    UScriptCode code;
+};
+
+struct ExpectedRun {
+    unsigned limit;
+    UScriptCode code;
+
+    ExpectedRun(unsigned the_limit, UScriptCode the_code)
+        : limit(the_limit)
+        , code(the_code)
+    {
+    }
+};
+
+class MockScriptData : public ScriptData {
+public:
+    ~MockScriptData() override {}
+
+    static const MockScriptData* instance()
+    {
+        AtomicallyInitializedStaticReference(const MockScriptData, mockScriptData, (new MockScriptData()));
+
+        return &mockScriptData;
+    }
+
+    void getScripts(UChar32 ch, Vector<UScriptCode>& dst) const override
+    {
+        ASSERT(ch >= kMockCharMin);
+        ASSERT(ch < kMockCharLimit);
+
+        int code = ch - kMockCharMin;
+        dst.clear();
+        switch (code & kCodeSpecialMask) {
+        case kCodeSpecialCommon:
+            dst.append(USCRIPT_COMMON);
+            break;
+        case kCodeSpecialInherited:
+            dst.append(USCRIPT_INHERITED);
+            break;
+        default:
+            break;
+        }
+        int listBits = kTable[code & kCodeListIndexMask];
+        if (dst.isEmpty() && listBits == 0) {
+            dst.append(USCRIPT_UNKNOWN);
+            return;
+        }
+        while (listBits) {
+            switch (listBits & kListMask) {
+            case 0:
+                break;
+            case kLatin:
+                dst.append(USCRIPT_LATIN);
+                break;
+            case kHan:
+                dst.append(USCRIPT_HAN);
+                break;
+            case kGreek:
+                dst.append(USCRIPT_GREEK);
+                break;
+            }
+            listBits >>= kListShift;
+        }
+    }
+
+    UChar32 getPairedBracket(UChar32 ch) const override
+    {
+        switch (getPairedBracketType(ch)) {
+        case PairedBracketType::BracketTypeClose:
+            return ch - kBracketDelta;
+        case PairedBracketType::BracketTypeOpen:
+            return ch + kBracketDelta;
+        default:
+            return ch;
+        }
+    }
+
+    PairedBracketType getPairedBracketType(UChar32 ch) const override
+    {
+        ASSERT(ch >= kMockCharMin && ch < kMockCharLimit);
+        int code = ch - kMockCharMin;
+        if ((code & kCodeBracketBit) == 0) {
+            return PairedBracketType::BracketTypeNone;
+        }
+        if (code & kCodeBracketCloseBit) {
+            return PairedBracketType::BracketTypeClose;
+        }
+        return PairedBracketType::BracketTypeOpen;
+    }
+
+    static int TableLookup(int value)
+    {
+        for (int i = 0; i < 16; ++i) {
+            if (kTable[i] == value) {
+                return i;
+            }
+        }
+        WTF_LOG_ERROR("Table does not contain value 0x%x", value);
+        return 0;
+    }
+
+    static String ToTestString(const std::string& input)
+    {
+        String result(String::make16BitFrom8BitSource(0, 0));
+        bool inSet = false;
+        int seen = 0;
+        int code = 0;
+        int list = 0;
+        int currentShift = 0;
+        for (char c : input) {
+            if (inSet) {
+                switch (c) {
+                case '(':
+                    ASSERT(seen == 0);
+                    seen |= kSawBracket;
+                    code |= kCodeBracketBit;
+                    break;
+                case '[':
+                    ASSERT(seen == 0);
+                    seen |= kSawBracket;
+                    code |= kCodeBracketBit | kCodeSquareBracketBit;
+                    break;
+                case ')':
+                    ASSERT(seen == 0);
+                    seen |= kSawBracket;
+                    code |= kCodeBracketBit | kCodeBracketCloseBit;
+                    break;
+                case ']':
+                    ASSERT(seen == 0);
+                    seen |= kSawBracket;
+                    code |= kCodeBracketBit | kCodeSquareBracketBit | kCodeBracketCloseBit;
+                    break;
+                case 'i':
+                    ASSERT(seen == 0); // brackets can't be inherited
+                    seen |= kSawSpecial;
+                    code |= kCodeSpecialInherited;
+                    break;
+                case 'c':
+                    ASSERT((seen & ~kSawBracket) == 0);
+                    seen |= kSawSpecial;
+                    code |= kCodeSpecialCommon;
+                    break;
+                case 'l':
+                    ASSERT((seen & kSawLatin) == 0);
+                    ASSERT(currentShift < 3);
+                    seen |= kSawLatin;
+                    list |= kLatin << (2 * currentShift++);
+                    break;
+                case 'h':
+                    ASSERT((seen & kSawHan) == 0);
+                    ASSERT(currentShift < 3);
+                    seen |= kSawHan;
+                    list |= kHan << (2 * currentShift++);
+                    break;
+                case 'g':
+                    ASSERT((seen & kSawGreek) == 0);
+                    ASSERT(currentShift < 3);
+                    seen |= kSawGreek;
+                    list |= kGreek << (2 * currentShift++);
+                    break;
+                case '>':
+                    ASSERT(seen != 0);
+                    code |= TableLookup(list);
+                    result.append(static_cast<UChar>(kMockCharMin + code));
+                    inSet = false;
+                    break;
+                default:
+                    WTF_LOG_ERROR("Illegal mock string set char: '%c'", c);
+                    break;
+                }
+                continue;
+            }
+            // not in set
+            switch (c) {
+            case '<':
+                seen = 0;
+                code = 0;
+                list = 0;
+                currentShift = 0;
+                inSet = true;
+                break;
+            case '(':
+                code = kCodeBracketBit | kCodeSpecialCommon;
+                break;
+            case '[':
+                code = kCodeBracketBit | kCodeSquareBracketBit | kCodeSpecialCommon;
+                break;
+            case ')':
+                code = kCodeBracketBit | kCodeBracketCloseBit | kCodeSpecialCommon;
+                break;
+            case ']':
+                code = kCodeBracketBit | kCodeSquareBracketBit | kCodeBracketCloseBit | kCodeSpecialCommon;
+                break;
+            case 'i':
+                code = kCodeSpecialInherited;
+                break;
+            case 'c':
+                code = kCodeSpecialCommon;
+                break;
+            case 'l':
+                code = kLatin;
+                break;
+            case 'h':
+                code = kHan;
+                break;
+            case 'g':
+                code = kGreek;
+                break;
+            case '?':
+                code = 0; // unknown
+                break;
+            default:
+                WTF_LOG_ERROR("Illegal mock string set char: '%c'", c);
+            }
+            if (!inSet) {
+                result.append(static_cast<UChar>(kMockCharMin + code));
+            }
+        }
+        return result;
+    }
+
+    static std::string MockCharString(UChar mockch)
+    {
+        ASSERT(mockch >= kMockCharMin && mockch < kMockCharLimit);
+        int code = mockch - kMockCharMin;
+
+        // We use set notation in these cases:
+        // - more than one of special, kLatin, kHan, kGreek
+        // - bracket and not common (since non-set brackets are common)
+        bool isBracket = (code & kCodeBracketBit) != 0;
+        bool isSpecial = (mockch & kCodeSpecialMask) != 0;
+        bool isCommon = (mockch & kCodeSpecialMask) == kCodeSpecialCommon;
+        char c;
+        if (isBracket) {
+            if (code & kCodeSquareBracketBit) {
+                if (code & kCodeBracketCloseBit) {
+                    c = ']';
+                } else {
+                    c = '[';
+                }
+            } else {
+                if (code & kCodeBracketCloseBit) {
+                    c = ')';
+                } else {
+                    c = '(';
+                }
+            }
+        } else if (isSpecial) {
+            c = isCommon ? 'c' : 'i';
+        }
+        std::string result;
+        int listBits = kTable[code & kCodeListIndexMask];
+        while (listBits) {
+            switch (listBits & kListMask) {
+            case 0:
+                break;
+            case kLatin:
+                result += 'l';
+                break;
+            case kHan:
+                result += 'h';
+                break;
+            case kGreek:
+                result += 'g';
+                break;
+            }
+            listBits >>= kListShift;
+        }
+        bool needSet = result.length() + (isSpecial ? 1 : 0) > 1 || (isBracket && (result.length() > 0 || !isCommon));
+        if (needSet) {
+            std::string setResult("<");
+            if (isBracket) {
+                setResult += c;
+            }
+            if (isSpecial) {
+                if (isCommon) {
+                    setResult += "c";
+                } else {
+                    setResult += "i";
+                }
+            }
+            setResult += result;
+            setResult += ">";
+            return setResult;
+        }
+        if (isBracket || isSpecial) {
+            result = c;
+        }
+        return result;
+    }
+
+    // We determine properties based on the offset from kMockCharMin:
+    // bits 0-3 represent the list of l, h, c scripts (index into table)
+    // bit 4-5 means: 0 plain, 1 common, 2 inherited, 3 illegal
+    // bit 6 clear means non-bracket, open means bracket
+    // bit 7 clear means open bracket, set means close bracket
+    // bit 8 clear means paren, set means bracket
+    // if it's a bracket, the matching bracket is 64 code points away
+    static const UChar32 kMockCharMin = 0xe000;
+    static const UChar32 kMockCharLimit = kMockCharMin + 0x200;
+    static const int kLatin = 1;
+    static const int kHan = 2;
+    static const int kGreek = 3;
+    static const int kCodeListIndexMask = 0xf;
+    static const int kCodeSpecialMask = 0x30;
+    static const int kCodeSpecialCommon = 0x10;
+    static const int kCodeSpecialInherited = 0x20;
+    static const int kCodeBracketCloseBit = 0x40;
+    static const int kCodeBracketBit = 0x80;
+    static const int kCodeSquareBracketBit = 0x100;
+    static const int kListShift = 2;
+    static const int kListMask = 0x3;
+    static const int kBracketDelta = kCodeBracketCloseBit;
+    static const int kTable[16];
+
+    static const int kSawBracket = 0x1;
+    static const int kSawSpecial = 0x2;
+    static const int kSawLatin = 0x4;
+    static const int kSawHan = 0x8;
+    static const int kSawGreek = 0x10;
+};
+
+static const int kLatin2 = MockScriptData::kLatin << 2;
+static const int kHan2 = MockScriptData::kHan << 2;
+static const int kGreek2 = MockScriptData::kGreek << 2;
+static const int kLatin3 = MockScriptData::kLatin << 4;
+static const int kHan3 = MockScriptData::kHan << 4;
+static const int kGreek3 = MockScriptData::kGreek << 4;
+const int MockScriptData::kTable[] = {
+    0, kLatin, kHan, kGreek,
+    kLatin2 + kHan, kLatin2 + kGreek,
+    kHan2 + kLatin, kHan2 + kGreek,
+    kGreek2 + kLatin, kGreek2 + kHan,
+    kLatin3 + kHan2 + kGreek, kLatin3 + kGreek2 + kHan,
+    kHan3 + kLatin2 + kGreek, kHan3 + kGreek2 + kLatin,
+    kGreek3 + kLatin2 + kHan, kGreek3 + kHan2 + kLatin,
+};
+
+class ScriptRunIteratorTest : public testing::Test {
+protected:
+    void CheckRuns(const std::vector<TestRun>& runs)
+    {
+        String text(String::make16BitFrom8BitSource(0, 0));
+        std::vector<ExpectedRun> expect;
+        for (auto& run : runs) {
+            text.append(String::fromUTF8(run.text.c_str()));
+            expect.push_back(ExpectedRun(text.length(), run.code));
+        }
+        ScriptRunIterator scriptRunIterator(text.characters16(), text.length());
+        VerifyRuns(&scriptRunIterator, expect);
+    }
+
+    // FIXME crbug.com/527329 - CheckMockRuns should be replaced by finding
+    // suitable equivalent real codepoint sequences instead.
+    void CheckMockRuns(const std::vector<TestRun>& runs)
+    {
+        String text(String::make16BitFrom8BitSource(0, 0));
+        std::vector<ExpectedRun> expect;
+        for (const TestRun& run : runs) {
+            text.append(MockScriptData::ToTestString(run.text));
+            expect.push_back({ text.length(), run.code });
+        }
+
+        ScriptRunIterator scriptRunIterator(text.characters16(), text.length(),
+            MockScriptData::instance());
+        VerifyRuns(&scriptRunIterator, expect);
+    }
+
+    void VerifyRuns(ScriptRunIterator* scriptRunIterator,
+        const std::vector<ExpectedRun>& expect)
+    {
+        unsigned limit;
+        UScriptCode code;
+        unsigned long runCount = 0;
+        while (scriptRunIterator->consume(limit, code)) {
+            ASSERT_LT(runCount, expect.size());
+            ASSERT_EQ(expect[runCount].limit, limit);
+            ASSERT_EQ(expect[runCount].code, code);
+            ++runCount;
+        }
+        WTF_LOG_ERROR("Expected %zu runs, got %lu ", expect.size(), runCount);
+        ASSERT_EQ(expect.size(), runCount);
+    }
+};
+
+TEST_F(ScriptRunIteratorTest, Empty)
+{
+    String empty(String::make16BitFrom8BitSource(0, 0));
+    ScriptRunIterator scriptRunIterator(empty.characters16(), empty.length());
+    unsigned limit = 0;
+    UScriptCode code = USCRIPT_INVALID_CODE;
+    ASSERT(!scriptRunIterator.consume(limit, code));
+    ASSERT_EQ(limit, 0u);
+    ASSERT_EQ(code, USCRIPT_INVALID_CODE);
+}
+
+// Some of our compilers cannot initialize a vector from an array yet.
+#define DECLARE_RUNSVECTOR(...)                     \
+    static const TestRun runsArray[] = __VA_ARGS__; \
+    std::vector<TestRun> runs(runsArray, runsArray + sizeof(runsArray) / sizeof(*runsArray));
+
+#define CHECK_RUNS(...)              \
+    DECLARE_RUNSVECTOR(__VA_ARGS__); \
+    CheckRuns(runs);
+
+#define CHECK_MOCK_RUNS(...)         \
+    DECLARE_RUNSVECTOR(__VA_ARGS__); \
+    CheckMockRuns(runs);
+
+TEST_F(ScriptRunIteratorTest, Whitespace)
+{
+    CHECK_RUNS({ { " \t ", USCRIPT_COMMON } });
+}
+
+TEST_F(ScriptRunIteratorTest, Common)
+{
+    CHECK_RUNS({ { " ... !?", USCRIPT_COMMON } });
+}
+
+TEST_F(ScriptRunIteratorTest, Latin)
+{
+    CHECK_RUNS({ { "latin", USCRIPT_LATIN } });
+}
+
+TEST_F(ScriptRunIteratorTest, Chinese)
+{
+    CHECK_RUNS({ { "萬國碼", USCRIPT_HAN } });
+}
+
+// Close bracket without matching open is ignored
+TEST_F(ScriptRunIteratorTest, UnbalancedParens1)
+{
+    CHECK_RUNS({ { "(萬", USCRIPT_HAN },
+        { "a]", USCRIPT_LATIN },
+        { ")", USCRIPT_HAN } });
+}
+
+// Open bracket without matching close is popped when inside
+// matching close brackets, so doesn't match later close.
+TEST_F(ScriptRunIteratorTest, UnbalancedParens2)
+{
+    CHECK_RUNS({ { "(萬", USCRIPT_HAN },
+        { "a[", USCRIPT_LATIN },
+        { ")]", USCRIPT_HAN } });
+}
+
+// space goes with leading script
+TEST_F(ScriptRunIteratorTest, LatinHan)
+{
+    CHECK_RUNS({ { "Unicode ", USCRIPT_LATIN },
+        { "萬國碼", USCRIPT_HAN } });
+}
+
+// space goes with leading script
+TEST_F(ScriptRunIteratorTest, HanLatin)
+{
+    CHECK_RUNS({ { "萬國碼 ", USCRIPT_HAN },
+        { "Unicode", USCRIPT_LATIN } });
+}
+
+TEST_F(ScriptRunIteratorTest, ParenEmptyParen)
+{
+    CHECK_RUNS({ { "()", USCRIPT_COMMON } });
+}
+
+TEST_F(ScriptRunIteratorTest, ParenChineseParen)
+{
+    CHECK_RUNS({ { "(萬國碼)", USCRIPT_HAN } });
+}
+
+TEST_F(ScriptRunIteratorTest, ParenLatinParen)
+{
+    CHECK_RUNS({ { "(Unicode)", USCRIPT_LATIN } });
+}
+
+// open paren gets leading script
+TEST_F(ScriptRunIteratorTest, LatinParenChineseParen)
+{
+    CHECK_RUNS({ { "Unicode (", USCRIPT_LATIN },
+        { "萬國碼", USCRIPT_HAN },
+        { ")", USCRIPT_LATIN } });
+}
+
+// open paren gets first trailing script if no leading script
+TEST_F(ScriptRunIteratorTest, ParenChineseParenLatin)
+{
+    CHECK_RUNS({ { "(萬國碼) ", USCRIPT_HAN },
+        { "Unicode", USCRIPT_LATIN } });
+}
+
+// leading common and open paren get first trailing script.
+// TODO(dougfelt): we don't do quote matching, but probably should figure out
+// something better then doing nothing.
+TEST_F(ScriptRunIteratorTest, QuoteParenChineseParenLatinQuote)
+{
+    CHECK_RUNS({ { "\"(萬國碼) ", USCRIPT_HAN },
+        { "Unicode\"", USCRIPT_LATIN } });
+}
+
+// Unmatched close brace gets leading context
+TEST_F(ScriptRunIteratorTest, UnmatchedClose)
+{
+    CHECK_RUNS({ { "Unicode (", USCRIPT_LATIN },
+        { "萬國碼] ", USCRIPT_HAN },
+        { ") Unicode\"", USCRIPT_LATIN } });
+}
+
+// Match up to 32 bracket pairs
+TEST_F(ScriptRunIteratorTest, Match32Brackets)
+{
+    CHECK_RUNS({ { "[萬國碼 ", USCRIPT_HAN },
+        { "Unicode (((((((((((((((((((((((((((((((!"
+        ")))))))))))))))))))))))))))))))",
+        USCRIPT_LATIN },
+        { "]", USCRIPT_HAN } });
+}
+
+// Matches 32 most recent bracket pairs. More than that, and we revert to
+// surrounding script.
+TEST_F(ScriptRunIteratorTest, Match32MostRecentBrackets)
+{
+    CHECK_RUNS({ { "((([萬國碼 ", USCRIPT_HAN },
+        { "Unicode (((((((((((((((((((((((((((((((", USCRIPT_LATIN },
+        { "萬國碼!", USCRIPT_HAN },
+        { ")))))))))))))))))))))))))))))))", USCRIPT_LATIN },
+        { "]", USCRIPT_HAN },
+        { "But )))", USCRIPT_LATIN } });
+}
+
+// A char with multiple scripts that match both leading and trailing context
+// gets the leading context.
+TEST_F(ScriptRunIteratorTest, ExtensionsPreferLeadingContext)
+{
+    CHECK_MOCK_RUNS({ { "h<lh>", USCRIPT_HAN },
+        { "l", USCRIPT_LATIN } });
+}
+
+// A char with multiple scripts that only match trailing context gets the
+// trailing context.
+TEST_F(ScriptRunIteratorTest, ExtensionsMatchTrailingContext)
+{
+    CHECK_MOCK_RUNS({ { "h", USCRIPT_HAN },
+        { "<gl>l", USCRIPT_LATIN } });
+}
+
+// Retain first established priority script.  <lhg><gh> produce the script <gh>
+// with g as priority, because of the two priority scripts l and g, only g
+// remains.  Then <gh><hgl> retains g as priority, because of the two priority
+// scripts g and h that remain, g was encountered first.
+TEST_F(ScriptRunIteratorTest, ExtensionsRetainFirstPriorityScript)
+{
+    CHECK_MOCK_RUNS({ { "<lhg><gh><hgl>", USCRIPT_GREEK } });
+}
+
+// Parens can have scripts that break script runs.
+TEST_F(ScriptRunIteratorTest, ExtensionsParens)
+{
+    CHECK_MOCK_RUNS({ { "<gl><(lg>", USCRIPT_GREEK },
+        { "h<[hl>", USCRIPT_HAN },
+        { "l", USCRIPT_LATIN },
+        { "<]hl>", USCRIPT_HAN },
+        { "<)lg>", USCRIPT_GREEK } });
+}
+
+// The close paren might be encountered before we've established the open
+// paren's script, but when this is the case the current set is still valid, so
+// this doesn't affect it nor break the run.
+TEST_F(ScriptRunIteratorTest, ExtensionsParens2)
+{
+    CHECK_MOCK_RUNS({ { "<(lhg><gh><)lhg>", USCRIPT_GREEK } });
+}
+
+// A common script with a single extension should be treated as common, but
+// with the extended script as a default.  If we encounter anything other than
+// common, that takes priority.  If we encounter other common scripts with a
+// single extension, the current priority remains.
+TEST_F(ScriptRunIteratorTest, CommonWithPriority)
+{
+    CHECK_MOCK_RUNS({ { "<ch>", USCRIPT_HAN } });
+}
+
+TEST_F(ScriptRunIteratorTest, CommonWithPriority2)
+{
+    CHECK_MOCK_RUNS({ { "<ch><lh>", USCRIPT_LATIN } });
+}
+
+TEST_F(ScriptRunIteratorTest, CommonWithPriority3)
+{
+    CHECK_MOCK_RUNS({ { "<ch><cl><cg>", USCRIPT_HAN } });
+}
+
+// UDatta (\xE0\xA5\x91) is inherited with LATIN and DEVANAGARI extensions.
+// Since it has LATIN, and the dotted circle (\xE2\x97\x8C) is COMMON and has
+// adopted the preceding LATIN, it gets the LATIN. This is standard.
+TEST_F(ScriptRunIteratorTest, LatinDottedCircleUdatta)
+{
+    CHECK_RUNS({ { "Latin \xE2\x97\x8C\xE0\xA5\x91", USCRIPT_LATIN } });
+}
+
+// In this situation, UDatta (\xE0\xA5\x91) doesn't share a script with the
+// value inherited by the dotted circle (\xE2\x97\x8C). It captures the
+// preceding dotted circle and breaks it from the run it would normally have
+// been in.
+TEST_F(ScriptRunIteratorTest, HanDottedCircleUdatta)
+{
+    CHECK_RUNS({ { "萬國碼 ", USCRIPT_HAN },
+        { "\xE2\x97\x8C\xE0\xA5\x91", USCRIPT_DEVANAGARI } });
+}
+
+// Tatweel is \xD9\x80 Lm, Fathatan is \xD9\x8B Mn. The script of tatweel is
+// common, that of Fathatan is inherited.  The script extensions for Fathatan
+// are Arabic and Syriac. The Syriac script is 34 in ICU, Arabic is 2. So the
+// preferred script for Fathatan is Arabic, according to Behdad's
+// heuristic. This is exactly analogous to the Udatta tests above, except
+// Tatweel is Lm. But we don't take properties into account, only scripts.
+TEST_F(ScriptRunIteratorTest, LatinTatweelFathatan)
+{
+    CHECK_RUNS({ { "Latin ", USCRIPT_LATIN },
+        { "\xD9\x80\xD9\x8B", USCRIPT_ARABIC } });
+}
+
+// Another case where if the mark accepts a script that was inherited by the
+// preceding common-script character, they both continue in that script.
+// SYRIAC LETTER NUN \xDC\xA2
+// ARABIC TATWEEL \xD9\x80
+// ARABIC FATHATAN \xD9\x82
+TEST_F(ScriptRunIteratorTest, SyriacTatweelFathatan)
+{
+    CHECK_RUNS({ { "\xDC\xA2\xD9\x80\xD9\x8B", USCRIPT_SYRIAC } });
+}
+
+// The Udatta (\xE0\xA5\x91) is inherited, so will share runs with anything that
+// is not common.
+TEST_F(ScriptRunIteratorTest, HanUdatta)
+{
+    CHECK_RUNS({ { "萬國碼\xE0\xA5\x91", USCRIPT_HAN } });
+}
+
+// The Udatta (\xE0\xA5\x91) is inherited, and will capture the space and turn
+// it into Devanagari.
+TEST_F(ScriptRunIteratorTest, HanSpaceUdatta)
+{
+    CHECK_RUNS({ { "萬國碼", USCRIPT_HAN },
+        { " \xE0\xA5\x91", USCRIPT_DEVANAGARI } });
+}
+
+// Make sure Mock code works too.
+TEST_F(ScriptRunIteratorTest, MockHanInheritedGL)
+{
+    CHECK_MOCK_RUNS({ { "h<igl>", USCRIPT_HAN } });
+}
+
+TEST_F(ScriptRunIteratorTest, MockHanCommonInheritedGL)
+{
+    CHECK_MOCK_RUNS({ { "h", USCRIPT_HAN },
+        { "c<igl>", USCRIPT_GREEK } });
+}
+
+// Leading inherited just act like common, except there's no preferred script.
+TEST_F(ScriptRunIteratorTest, MockLeadingInherited)
+{
+    CHECK_MOCK_RUNS({ { "<igl>", USCRIPT_COMMON } });
+}
+
+// Leading inherited just act like common, except there's no preferred script.
+TEST_F(ScriptRunIteratorTest, MockLeadingInherited2)
+{
+    CHECK_MOCK_RUNS({ { "<igl><ih>", USCRIPT_COMMON } });
+}
+
+TEST_F(ScriptRunIteratorTest, LeadingInheritedHan)
+{
+    // DEVANAGARI STRESS SIGN UDATTA \xE0\xA5\x91
+    CHECK_RUNS({ { "\xE0\xA5\x91萬國碼", USCRIPT_HAN } });
+}
+
+TEST_F(ScriptRunIteratorTest, LeadingInheritedHan2)
+{
+    // DEVANAGARI STRESS SIGN UDATTA \xE0\xA5\x91
+    // ARABIC FATHATAN \xD9\x8B
+    CHECK_RUNS({ { "\xE0\xA5\x91\xD9\x8B萬國碼", USCRIPT_HAN } });
+}
+
+TEST_F(ScriptRunIteratorTest, OddLatinString)
+{
+    CHECK_RUNS({ { "ç̈", USCRIPT_LATIN } });
+}
+
+class ScriptRunIteratorICUDataTest : public testing::Test {
+public:
+    ScriptRunIteratorICUDataTest()
+        : m_maxExtensions(0)
+        , m_maxExtensionsCodepoint(0xffff)
+    {
+        int maxExtensions = 0;
+        UChar32 m_maxExtensionscp = 0;
+        for (UChar32 cp = 0; cp < 0x11000; ++cp) {
+            UErrorCode status = U_ZERO_ERROR;
+            int count = uscript_getScriptExtensions(cp, 0, 0, &status);
+            if (count > maxExtensions) {
+                maxExtensions = count;
+                m_maxExtensionscp = cp;
+            }
+        }
+        m_maxExtensions = maxExtensions;
+        m_maxExtensionsCodepoint = m_maxExtensionscp;
+    }
+
+protected:
+    UChar32 GetACharWithMaxExtensions(int* numExtensions)
+    {
+        if (numExtensions) {
+            *numExtensions = m_maxExtensions;
+        }
+        return m_maxExtensionsCodepoint;
+    }
+
+private:
+    int m_maxExtensions;
+    UChar32 m_maxExtensionsCodepoint;
+};
+
+// Validate that ICU never returns more than our maximum expected number of
+// script extensions.
+TEST_F(ScriptRunIteratorICUDataTest, ValidateICUMaxScriptExtensions)
+{
+    int maxExtensions;
+    UChar32 cp = GetACharWithMaxExtensions(&maxExtensions);
+    ASSERT_LE(maxExtensions, ScriptData::kMaxScriptCount)
+        << "char " << std::hex << cp << std::dec;
+}
+
+// Check that ICUScriptData returns all of a character's scripts.
+// This only checks one likely character, but doesn't check all cases.
+TEST_F(ScriptRunIteratorICUDataTest, ICUDataGetScriptsReturnsAllExtensions)
+{
+    int maxExtensions;
+    UChar32 cp = GetACharWithMaxExtensions(&maxExtensions);
+    Vector<UScriptCode> extensions;
+    ICUScriptData::instance()->getScripts(cp, extensions);
+
+    // It's possible that GetScripts adds the primary script to the list of
+    // extensions, resulting in one more script than the raw extension count.
+    ASSERT_GE(static_cast<int>(extensions.size()), maxExtensions)
+        << "char " << std::hex << cp << std::dec;
+}
+
+TEST_F(ScriptRunIteratorICUDataTest, CommonHaveNoMoreThanOneExtension)
+{
+    Vector<UScriptCode> extensions;
+    for (UChar32 cp = 0; cp < 0x110000; ++cp) {
+        ICUScriptData::instance()->getScripts(cp, extensions);
+        UScriptCode primary = extensions.at(0);
+        if (primary == USCRIPT_COMMON) {
+            ASSERT_LE(extensions.size(), 2ul)
+                << "cp: " << std::hex << cp << std::dec;
+        }
+    }
+}
+
+// ZWJ is \u200D Cf (Format, other) and its script is inherited.  I'm going to
+// ignore this for now, as I think it shouldn't matter which run it ends up
+// in. HarfBuzz needs to be able to use it as context and shape each
+// neighboring character appropriately no matter what run it got assigned to.
+
+} // namespace blink