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GH-39149: [C++][Compute] Fix replace_substring hang on empty pattern #55442

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GH-39149: [C++][Compute] Fix replace_substring hang on empty pattern #55442

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7 changes: 6 additions & 1 deletion cpp/src/arrow/compute/kernels/scalar_string_ascii.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2039,6 +2039,10 @@ struct PlainSubstringReplacer {

static Result<std::unique_ptr<PlainSubstringReplacer>> Make(
const ReplaceSubstringOptions& options, bool is_utf8) {
if (options.pattern.empty()) {
// An empty pattern would match at every position without advancing.
return Status::Invalid("Empty substring pattern is not supported");
}
return std::make_unique<PlainSubstringReplacer>(options);
}

Expand Down Expand Up @@ -2119,7 +2123,8 @@ struct RegexSubstringReplacer {
re2::StringPiece replacement(options_.replacement);

// If s is empty, then it's essentially global
if (options_.max_replacements == -1 || s.empty()) {
// Any negative value means unlimited replacements.
if (options_.max_replacements < 0 || s.empty()) {
std::string s_copy{s.data(), s.length()};
RE2::GlobalReplace(&s_copy, regex_replacement_, replacement);
return builder->Append(reinterpret_cast<const uint8_t*>(s_copy.data()),
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12 changes: 12 additions & 0 deletions cpp/src/arrow/compute/kernels/scalar_string_test.cc
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Expand Up @@ -2102,6 +2102,13 @@ TYPED_TEST(TestBaseBinaryKernels, ReplaceSubstring) {

Datum input = ArrayFromJSON(this->type(), "[]");
ASSERT_RAISES(Invalid, CallFunction("replace_substring", {input}));

// GH-39149: an empty pattern used to loop forever
input = ArrayFromJSON(this->type(), R"(["abc", "", null])");
for (int64_t max_replacements : {-1, -3, 1}) {
options = ReplaceSubstringOptions{"", "x", max_replacements};
ASSERT_RAISES(Invalid, CallFunction("replace_substring", {input}, &options));
}
}

#ifdef ARROW_WITH_RE2
Expand All @@ -2120,6 +2127,11 @@ TYPED_TEST(TestBaseBinaryKernels, ReplaceSubstringRegex) {
this->CheckUnary("replace_substring_regex", R"([""])", this->type(), R"(["x"])",
&options);

// GH-39149: negative max_replacements other than -1 means unlimited
options = ReplaceSubstringOptions{"", "x", -3};
this->CheckUnary("replace_substring_regex", R"(["abc"])", this->type(),
R"(["xaxbxcx"])", &options);

// ARROW-12774
options = ReplaceSubstringOptions{"X", "Y"};
this->CheckUnary("replace_substring_regex",
Expand Down
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