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fix code unit/code point mix-up in cord substring length #2040

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fix code unit/code point mix-up in cord substring length #2040

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c2ae232
fix code unit/code point mix-up in cord substring length
sahvx655-wq Jun 2, 2026
cba6300
Add regression test for cord substring code unit length
sahvx655-wq Jun 23, 2026
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2 changes: 1 addition & 1 deletion common/values/string_value.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -742,7 +742,7 @@ absl::StatusOr<absl::Cord> SubstringImpl(const absl::Cord& cord, uint64_t start,
}
if (size_code_points == end) {
return cord.Subcord(start_code_units,
size_code_points - start_code_units);
size_code_units - start_code_units);
}
char32_t code_point;
size_t code_units;
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29 changes: 29 additions & 0 deletions common/values/string_value_test.cc
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Expand Up @@ -412,6 +412,35 @@ TEST_F(StringValueTest, CharAt) {
"<string>.charAt(<pos>): <pos> is less than 0")));
}

TEST_F(StringValueTest, Substring) {
using ::cel::test::ErrorValueIs;
using ::cel::test::StringValueIs;

// Each '€' is three bytes, so the cord built here is 18 bytes and is stored
// as a large (cord-backed) value. The substring length must be measured in
// code units, not code points, otherwise the cord overload truncates a
// multi-byte character or underflows the length.
StringValue unicode_cord = StringValue(absl::Cord("€€€€€€"));
StringValue unicode_view = StringValue("€€€€€€");

EXPECT_THAT(unicode_cord.Substring(0, 2), StringValueIs("€€"));
EXPECT_THAT(unicode_view.Substring(0, 2), StringValueIs("€€"));
EXPECT_THAT(unicode_cord.Substring(1, 2), StringValueIs("€"));
EXPECT_THAT(unicode_view.Substring(1, 2), StringValueIs("€"));
EXPECT_THAT(unicode_cord.Substring(2, 4), StringValueIs("€€"));
EXPECT_THAT(unicode_view.Substring(2, 4), StringValueIs("€€"));
EXPECT_THAT(unicode_cord.Substring(2), StringValueIs("€€€€"));
EXPECT_THAT(unicode_view.Substring(2), StringValueIs("€€€€"));

EXPECT_THAT(unicode_cord.Substring(0, 7),
ErrorValueIs(absl::InvalidArgumentError(
"<string>.substring(<start>, <end>): <start> or <end> is "
"greater than <string>.size()")));
EXPECT_THAT(unicode_cord.Substring(-1),
ErrorValueIs(absl::InvalidArgumentError(
"<string>.substring(<start>): <start> is less than 0")));
}

TEST_F(StringValueTest, Join) {
using ::cel::runtime_internal::CreateNoMatchingOverloadError;
using ::cel::test::ErrorValueIs;
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