[libcxx-commits] [libcxx] e9adcc4 - [libc++][regex] Correctly adjust match prefix for zero-length matches. (#94550)
via libcxx-commits
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Fri Jun 7 08:15:06 PDT 2024
Author: Konstantin Varlamov
Date: 2024-06-07T11:15:02-04:00
New Revision: e9adcc488f96a9f2b8c4344f5e3c7ca6639b9562
URL: https://github.com/llvm/llvm-project/commit/e9adcc488f96a9f2b8c4344f5e3c7ca6639b9562
DIFF: https://github.com/llvm/llvm-project/commit/e9adcc488f96a9f2b8c4344f5e3c7ca6639b9562.diff
LOG: [libc++][regex] Correctly adjust match prefix for zero-length matches. (#94550)
For regex patterns that produce zero-length matches, there is one
(imaginary) match in-between every character in the sequence being
searched (as well as before the first character and after the last
character). It's easiest to demonstrate using replacement:
`std::regex_replace("abc"s, "!", "")` should produce `!a!b!c!`, where
each exclamation mark makes a zero-length match visible.
Currently our implementation doesn't correctly set the prefix of each
zero-length match, "swallowing" the characters separating the imaginary
matches -- e.g. when going through zero-length matches within `abc`, the
corresponding prefixes should be `{'', 'a', 'b', 'c'}`, but before this
patch they will all be empty (`{'', '', '', ''}`). This happens in the
implementation of `regex_iterator::operator++`. Note that the Standard
spells out quite explicitly that the prefix might need to be adjusted
when dealing with zero-length matches in
[`re.regiter.incr`](http://eel.is/c++draft/re.regiter.incr):
> In all cases in which the call to `regex_search` returns `true`,
`match.prefix().first` shall be equal to the previous value of
`match[0].second`... It is unspecified how the implementation makes
these adjustments.
[Reproduction example](https://godbolt.org/z/8ve6G3dav)
```cpp
#include <iostream>
#include <regex>
#include <string>
int main() {
std::string str = "abc";
std::regex empty_matching_pattern("");
{ // The underlying problem is that `regex_iterator::operator++` doesn't update
// the prefix correctly.
std::sregex_iterator i(str.begin(), str.end(), empty_matching_pattern), e;
std::cout << "\"";
for (; i != e; ++i) {
const std::ssub_match& prefix = i->prefix();
std::cout << prefix.str();
}
std::cout << "\"\n";
// Before the patch: ""
// After the patch: "abc"
}
{ // `regex_replace` makes the problem very visible.
std::string replaced = std::regex_replace(str, empty_matching_pattern, "!");
std::cout << "\"" << replaced << "\"\n";
// Before the patch: "!!!!"
// After the patch: "!a!b!c!"
}
}
```
Fixes #64451
rdar://119912002
Added:
libcxx/test/std/re/re.alg/re.alg.replace/zero_length_matches.pass.cpp
Modified:
libcxx/include/regex
libcxx/test/std/re/re.iter/re.regiter/re.regiter.incr/post.pass.cpp
Removed:
################################################################################
diff --git a/libcxx/include/regex b/libcxx/include/regex
index b3869d36de1df..46968357d3974 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -4700,6 +4700,9 @@ private:
template <class, class>
friend class __lookahead;
+
+ template <class, class, class>
+ friend class regex_iterator;
};
template <class _BidirectionalIterator, class _Allocator>
@@ -5410,7 +5413,9 @@ template <class _BidirectionalIterator, class _CharT, class _Traits>
regex_iterator<_BidirectionalIterator, _CharT, _Traits>&
regex_iterator<_BidirectionalIterator, _CharT, _Traits>::operator++() {
__flags_ |= regex_constants::__no_update_pos;
- _BidirectionalIterator __start = __match_[0].second;
+ _BidirectionalIterator __start = __match_[0].second;
+ _BidirectionalIterator __prefix_start = __start;
+
if (__match_[0].first == __match_[0].second) {
if (__start == __end_) {
__match_ = value_type();
@@ -5424,9 +5429,21 @@ regex_iterator<_BidirectionalIterator, _CharT, _Traits>::operator++() {
else
++__start;
}
+
__flags_ |= regex_constants::match_prev_avail;
- if (!std::regex_search(__start, __end_, __match_, *__pregex_, __flags_))
+ if (!std::regex_search(__start, __end_, __match_, *__pregex_, __flags_)) {
__match_ = value_type();
+
+ } else {
+ // The Standard mandates that if `regex_search` returns true ([re.regiter.incr]), "`match.prefix().first` shall be
+ // equal to the previous value of `match[0].second`... It is unspecified how the implementation makes these
+ // adjustments." The adjustment is necessary if we incremented `__start` above (the branch that deals with
+ // zero-length matches).
+ auto& __prefix = __match_.__prefix_;
+ __prefix.first = __prefix_start;
+ __prefix.matched = __prefix.first != __prefix.second;
+ }
+
return *this;
}
diff --git a/libcxx/test/std/re/re.alg/re.alg.replace/zero_length_matches.pass.cpp b/libcxx/test/std/re/re.alg/re.alg.replace/zero_length_matches.pass.cpp
new file mode 100644
index 0000000000000..2f1b6280deb78
--- /dev/null
+++ b/libcxx/test/std/re/re.alg/re.alg.replace/zero_length_matches.pass.cpp
@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <regex>
+
+// Test that replacing zero-length matches works correctly.
+
+#include <cassert>
+#include <regex>
+#include <string>
+#include "test_macros.h"
+
+int main(int, char**) {
+ // Various patterns that produce zero-length matches.
+ assert(std::regex_replace("abc", std::regex(""), "!") == "!a!b!c!");
+ assert(std::regex_replace("abc", std::regex("X*"), "!") == "!a!b!c!");
+ assert(std::regex_replace("abc", std::regex("X{0,3}"), "!") == "!a!b!c!");
+
+ // Replacement string has several characters.
+ assert(std::regex_replace("abc", std::regex(""), "[!]") == "[!]a[!]b[!]c[!]");
+
+ // Empty replacement string.
+ assert(std::regex_replace("abc", std::regex(""), "") == "abc");
+
+ // Empty input.
+ assert(std::regex_replace("", std::regex(""), "!") == "!");
+
+ // Not all matches are zero-length.
+ assert(std::regex_replace("abCabCa", std::regex("C*"), "!") == "!a!b!!a!b!!a!");
+
+ return 0;
+}
diff --git a/libcxx/test/std/re/re.iter/re.regiter/re.regiter.incr/post.pass.cpp b/libcxx/test/std/re/re.iter/re.regiter/re.regiter.incr/post.pass.cpp
index 9332158f0de95..aefe86f152980 100644
--- a/libcxx/test/std/re/re.iter/re.regiter/re.regiter.incr/post.pass.cpp
+++ b/libcxx/test/std/re/re.iter/re.regiter/re.regiter.incr/post.pass.cpp
@@ -17,102 +17,151 @@
#include <iterator>
#include "test_macros.h"
-int main(int, char**)
-{
- {
- std::regex phone_numbers("\\d{3}-\\d{4}");
- const char phone_book[] = "555-1234, 555-2345, 555-3456";
- std::cregex_iterator i(std::begin(phone_book), std::end(phone_book), phone_numbers);
- std::cregex_iterator i2 = i;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 0);
- assert((*i).str() == "555-1234");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- i++;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 10);
- assert((*i).str() == "555-2345");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- i++;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 20);
- assert((*i).str() == "555-3456");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- i++;
- assert(i == std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- }
- {
- std::regex phone_numbers("\\d{3}-\\d{4}");
- const char phone_book[] = "555-1234, 555-2345, 555-3456";
- std::cregex_iterator i(std::begin(phone_book), std::end(phone_book), phone_numbers);
- std::cregex_iterator i2 = i;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 0);
- assert((*i).str() == "555-1234");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- ++i;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 10);
- assert((*i).str() == "555-2345");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- ++i;
- assert(i != std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i).size() == 1);
- assert((*i).position() == 20);
- assert((*i).str() == "555-3456");
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- ++i;
- assert(i == std::cregex_iterator());
- assert(i2!= std::cregex_iterator());
- assert((*i2).size() == 1);
- assert((*i2).position() == 0);
- assert((*i2).str() == "555-1234");
- }
- { // https://llvm.org/PR33681
- std::regex rex(".*");
- const char foo[] = "foo";
+void validate_prefixes(const std::regex& empty_matching_pattern) {
+ const char source[] = "abc";
+
+ std::cregex_iterator i(source, source + 3, empty_matching_pattern);
+ assert(!i->prefix().matched);
+ assert(i->prefix().length() == 0);
+ assert(i->prefix().first == source);
+ assert(i->prefix().second == source);
+
+ ++i;
+ assert(i->prefix().matched);
+ assert(i->prefix().length() == 1);
+ assert(i->prefix().first == source);
+ assert(i->prefix().second == source + 1);
+ assert(i->prefix().str() == "a");
+
+ ++i;
+ assert(i->prefix().matched);
+ assert(i->prefix().length() == 1);
+ assert(i->prefix().first == source + 1);
+ assert(i->prefix().second == source + 2);
+ assert(i->prefix().str() == "b");
+
+ ++i;
+ assert(i->prefix().matched);
+ assert(i->prefix().length() == 1);
+ assert(i->prefix().first == source + 2);
+ assert(i->prefix().second == source + 3);
+ assert(i->prefix().str() == "c");
+
+ ++i;
+ assert(i == std::cregex_iterator());
+}
+
+void test_prefix_adjustment() {
+ // Check that we correctly adjust the match prefix when dealing with zero-length matches -- this is explicitly
+ // required by the Standard ([re.regiter.incr]: "In all cases in which the call to `regex_search` returns true,
+ // `match.prefix().first` shall be equal to the previous value of `match[0].second`"). For a pattern that matches
+ // empty sequences, there is an implicit zero-length match between every character in a string -- make sure the
+ // prefix of each of these matches (except the first one) is the preceding character.
+
+ // An empty pattern produces zero-length matches.
+ validate_prefixes(std::regex(""));
+ // Any character repeated zero or more times can produce zero-length matches.
+ validate_prefixes(std::regex("X*"));
+ validate_prefixes(std::regex("X{0,3}"));
+}
+
+int main(int, char**) {
+ {
+ std::regex phone_numbers("\\d{3}-\\d{4}");
+ const char phone_book[] = "555-1234, 555-2345, 555-3456";
+ std::cregex_iterator i(std::begin(phone_book), std::end(phone_book), phone_numbers);
+ std::cregex_iterator i2 = i;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 0);
+ assert((*i).str() == "555-1234");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ i++;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 10);
+ assert((*i).str() == "555-2345");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ i++;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 20);
+ assert((*i).str() == "555-3456");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ i++;
+ assert(i == std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ }
+ {
+ std::regex phone_numbers("\\d{3}-\\d{4}");
+ const char phone_book[] = "555-1234, 555-2345, 555-3456";
+ std::cregex_iterator i(std::begin(phone_book), std::end(phone_book), phone_numbers);
+ std::cregex_iterator i2 = i;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 0);
+ assert((*i).str() == "555-1234");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ ++i;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 10);
+ assert((*i).str() == "555-2345");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ ++i;
+ assert(i != std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i).size() == 1);
+ assert((*i).position() == 20);
+ assert((*i).str() == "555-3456");
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ ++i;
+ assert(i == std::cregex_iterator());
+ assert(i2 != std::cregex_iterator());
+ assert((*i2).size() == 1);
+ assert((*i2).position() == 0);
+ assert((*i2).str() == "555-1234");
+ }
+ { // https://llvm.org/PR33681
+ std::regex rex(".*");
+ const char foo[] = "foo";
// The -1 is because we don't want the implicit null from the array.
- std::cregex_iterator i(std::begin(foo), std::end(foo) - 1, rex);
- std::cregex_iterator e;
- assert(i != e);
- assert((*i).size() == 1);
- assert((*i).str() == "foo");
-
- ++i;
- assert(i != e);
- assert((*i).size() == 1);
- assert((*i).str() == "");
-
- ++i;
- assert(i == e);
- }
+ std::cregex_iterator i(std::begin(foo), std::end(foo) - 1, rex);
+ std::cregex_iterator e;
+ assert(i != e);
+ assert((*i).size() == 1);
+ assert((*i).str() == "foo");
+
+ ++i;
+ assert(i != e);
+ assert((*i).size() == 1);
+ assert((*i).str() == "");
+
+ ++i;
+ assert(i == e);
+ }
+
+ test_prefix_adjustment();
return 0;
}
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