From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 9 Feb 2026 10:48:44 +0000 (+0000)
Subject: libstdc++: Fix incorrect noexcept on string::compare overloads [PR123991]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0912dfcd1e901d7dc1ff5e10528eefe3f3ff7b22;p=thirdparty%2Fgcc.git

libstdc++: Fix incorrect noexcept on string::compare overloads [PR123991]

These compare overloads throw when the pos index is out of range, not
only when the const T& parameter throws on conversion to string_view.

Remove the incorrect conditional noexcept-specifier from the two
overloads that can throw.

libstdc++-v3/ChangeLog:

	PR libstdc++/123991
	* include/bits/basic_string.h (compare(size_type, size_type, T)):
	Remove noexcept-specifier.
	(compare(size_type, size_type, T, size_type, size_type)):
	Likewise.
	* include/bits/cow_string.h (compare(size_type, size_type, T)):
	Remove noexcept-specifier.
	(compare(size_type, size_type, T, size_type, size_type)):
	Likewise.
	* testsuite/21_strings/basic_string/operations/compare/char/123991.cc:
	New test.
	* testsuite/21_strings/basic_string/operations/compare/wchar_t/123991.cc:
	New test.

Reviewed-by: Nathan Myers <nmyers@redhat.com>
---

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 0602b0dcac8..cd6f312f1bd 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -3524,7 +3524,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	_GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
 	_If_sv<_Tp, int>
 	compare(size_type __pos, size_type __n, const _Tp& __svt) const
-	noexcept(is_same<_Tp, __sv_type>::value)
 	{
 	  __sv_type __sv = __svt;
 	  return __sv_type(*this).substr(__pos, __n).compare(__sv);
@@ -3545,7 +3544,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 	_If_sv<_Tp, int>
 	compare(size_type __pos1, size_type __n1, const _Tp& __svt,
 		size_type __pos2, size_type __n2 = npos) const
-	noexcept(is_same<_Tp, __sv_type>::value)
 	{
 	  __sv_type __sv = __svt;
 	  return __sv_type(*this)
diff --git a/libstdc++-v3/include/bits/cow_string.h b/libstdc++-v3/include/bits/cow_string.h
index 36c19fabfc5..6cf00224372 100644
--- a/libstdc++-v3/include/bits/cow_string.h
+++ b/libstdc++-v3/include/bits/cow_string.h
@@ -2998,7 +2998,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Tp>
 	_If_sv<_Tp, int>
 	compare(size_type __pos, size_type __n, const _Tp& __svt) const
-	noexcept(is_same<_Tp, __sv_type>::value)
 	{
 	  __sv_type __sv = __svt;
 	  return __sv_type(*this).substr(__pos, __n).compare(__sv);
@@ -3018,7 +3017,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	_If_sv<_Tp, int>
 	compare(size_type __pos1, size_type __n1, const _Tp& __svt,
 		size_type __pos2, size_type __n2 = npos) const
-	noexcept(is_same<_Tp, __sv_type>::value)
 	{
 	  __sv_type __sv = __svt;
 	  return __sv_type(*this)
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/char/123991.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/char/123991.cc
new file mode 100644
index 00000000000..53ef2d4606c
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/char/123991.cc
@@ -0,0 +1,56 @@
+// { dg-do run { target c++17 } }
+
+// Bug 123991 - std::string::compare crashes instead of throwing
+
+#include <string>
+#include <string_view>
+#include <stdexcept>
+#include <testsuite_hooks.h>
+
+void
+test_compare_3arg()
+{
+  std::string_view sv;
+  std::string s;
+  static_assert( ! noexcept(s.compare(0, 0, sv)) );
+#ifdef __cpp_exceptions
+  try
+  {
+    (void) s.compare(1, 0, sv);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+#endif
+}
+
+void
+test_compare_5arg()
+{
+  std::string_view sv;
+  std::string s;
+  static_assert( ! noexcept(s.compare(0, 0, sv, 0, 0)) );
+#ifdef __cpp_exceptions
+  try
+  {
+    (void) s.compare(1, 0, sv, 0, 0);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+
+  try
+  {
+    (void) s.compare(0, 0, sv, 1, 0);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+#endif
+}
+
+int main()
+{
+  test_compare_3arg();
+  test_compare_5arg();
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/wchar_t/123991.cc b/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/wchar_t/123991.cc
new file mode 100644
index 00000000000..c4188bbff8b
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/operations/compare/wchar_t/123991.cc
@@ -0,0 +1,56 @@
+// { dg-do run { target c++17 } }
+
+// Bug 123991 - std::string::compare crashes instead of throwing
+
+#include <string>
+#include <string_view>
+#include <stdexcept>
+#include <testsuite_hooks.h>
+
+void
+test_compare_3arg()
+{
+  std::wstring_view sv;
+  std::wstring s;
+  static_assert( ! noexcept(s.compare(0, 0, sv)) );
+#ifdef __cpp_exceptions
+  try
+  {
+    (void) s.compare(1, 0, sv);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+#endif
+}
+
+void
+test_compare_5arg()
+{
+  std::wstring_view sv;
+  std::wstring s;
+  static_assert( ! noexcept(s.compare(0, 0, sv, 0, 0)) );
+#ifdef __cpp_exceptions
+  try
+  {
+    (void) s.compare(1, 0, sv, 0, 0);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+
+  try
+  {
+    (void) s.compare(0, 0, sv, 1, 0);
+    VERIFY(false);
+  }
+  catch (const std::out_of_range&)
+  { }
+#endif
+}
+
+int main()
+{
+  test_compare_3arg();
+  test_compare_5arg();
+}