[clang-tidy] Fix `modernize-use-constraints` crash on uses of nonstandard `enable_if`s #152938

localspook · 2025-08-10T19:35:21Z

Fixes #152868. See that issue for details.
Fixes #123726.

…dard `enable_if`s

llvmbot · 2025-08-10T19:35:49Z

@llvm/pr-subscribers-clang-tools-extra

Author: Victor Chernyakin (localspook)

Changes

Fixes #152868. See that issue for details.

Full diff: https://github.com/llvm/llvm-project/pull/152938.diff

3 Files Affected:

(modified) clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp (+10)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
(modified) clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp (+30-1)

diff --git a/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
index e9b96c4016af6..ab25fb675552a 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
@@ -8,6 +8,7 @@
 
 #include "UseConstraintsCheck.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Lex/Lexer.h"
 
@@ -78,6 +79,15 @@ matchEnableIfSpecializationImplTypename(TypeLoc TheType) {
     if (!TD || TD->getName() != "enable_if")
       return std::nullopt;
 
+    const TemplateParameterList *Params = TD->getTemplateParameters();
+    if (Params->size() != 2)
+      return std::nullopt;
+
+    const auto *FirstParam =
+        dyn_cast<NonTypeTemplateParmDecl>(Params->getParam(0));
+    if (!FirstParam || !FirstParam->getType()->isBooleanType())
+      return std::nullopt;
+
     int NumArgs = SpecializationLoc.getNumArgs();
     if (NumArgs != 1 && NumArgs != 2)
       return std::nullopt;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 2de2818172850..f6aedb299e456 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -136,6 +136,11 @@ Changes in existing checks
 - Improved :doc:`misc-header-include-cycle
   <clang-tidy/checks/misc/header-include-cycle>` check performance.
 
+- Fixed a :doc:`modernize-use-constraints
+  <clang-tidy/checks/modernize/use-constraints>` crash on uses of
+  nonstandard ``enable_if``s with a signature different from
+  ``std::enable_if`` (such as ``boost::enable_if``).
+
 - Improved :doc:`modernize-use-designated-initializers
   <clang-tidy/checks/modernize/use-designated-initializers>` check to
   suggest using designated initializers for aliased aggregate types.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
index 3bcd5cd74024e..d61073c1aac3f 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy -std=c++20 %s modernize-use-constraints %t -- -- -fno-delayed-template-parsing
+// RUN: %check_clang_tidy -std=c++20-or-later %s modernize-use-constraints %t -- -- -fno-delayed-template-parsing
 
 // NOLINTBEGIN
 namespace std {
@@ -756,3 +756,32 @@ abs(const number<T, ExpressionTemplates> &v) {
 }
 
 }
+
+template <typename T>
+struct some_type_trait {
+  static constexpr bool value = true;
+};
+
+// Fix-its are offered even for a nonstandard enable_if.
+namespace nonstd {
+
+template <bool Condition, typename T = void>
+struct enable_if : std::enable_if<Condition, T> {};
+
+}
+
+template <typename T>
+typename nonstd::enable_if<some_type_trait<T>::value, void>::type nonstd_enable_if() {}
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use C++20 requires constraints instead of enable_if [modernize-use-constraints]
+// CHECK-FIXES: {{^}}void nonstd_enable_if() requires some_type_trait<T>::value {}{{$}}
+
+// But only if the nonstandard enable_if has the same signature as the standard one.
+namespace boost {
+
+template <typename Condition, typename T = void>
+struct enable_if : std::enable_if<Condition::value, T> {};
+
+}
+
+template <typename T>
+typename boost::enable_if<some_type_trait<T>, void>::type boost_enable_if() {}

llvmbot · 2025-08-10T19:35:50Z

@llvm/pr-subscribers-clang-tidy

Author: Victor Chernyakin (localspook)

Changes

Fixes #152868. See that issue for details.

Full diff: https://github.com/llvm/llvm-project/pull/152938.diff

3 Files Affected:

(modified) clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp (+10)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+5)
(modified) clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp (+30-1)

diff --git a/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
index e9b96c4016af6..ab25fb675552a 100644
--- a/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp
@@ -8,6 +8,7 @@
 
 #include "UseConstraintsCheck.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Lex/Lexer.h"
 
@@ -78,6 +79,15 @@ matchEnableIfSpecializationImplTypename(TypeLoc TheType) {
     if (!TD || TD->getName() != "enable_if")
       return std::nullopt;
 
+    const TemplateParameterList *Params = TD->getTemplateParameters();
+    if (Params->size() != 2)
+      return std::nullopt;
+
+    const auto *FirstParam =
+        dyn_cast<NonTypeTemplateParmDecl>(Params->getParam(0));
+    if (!FirstParam || !FirstParam->getType()->isBooleanType())
+      return std::nullopt;
+
     int NumArgs = SpecializationLoc.getNumArgs();
     if (NumArgs != 1 && NumArgs != 2)
       return std::nullopt;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 2de2818172850..f6aedb299e456 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -136,6 +136,11 @@ Changes in existing checks
 - Improved :doc:`misc-header-include-cycle
   <clang-tidy/checks/misc/header-include-cycle>` check performance.
 
+- Fixed a :doc:`modernize-use-constraints
+  <clang-tidy/checks/modernize/use-constraints>` crash on uses of
+  nonstandard ``enable_if``s with a signature different from
+  ``std::enable_if`` (such as ``boost::enable_if``).
+
 - Improved :doc:`modernize-use-designated-initializers
   <clang-tidy/checks/modernize/use-designated-initializers>` check to
   suggest using designated initializers for aliased aggregate types.
diff --git a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
index 3bcd5cd74024e..d61073c1aac3f 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy -std=c++20 %s modernize-use-constraints %t -- -- -fno-delayed-template-parsing
+// RUN: %check_clang_tidy -std=c++20-or-later %s modernize-use-constraints %t -- -- -fno-delayed-template-parsing
 
 // NOLINTBEGIN
 namespace std {
@@ -756,3 +756,32 @@ abs(const number<T, ExpressionTemplates> &v) {
 }
 
 }
+
+template <typename T>
+struct some_type_trait {
+  static constexpr bool value = true;
+};
+
+// Fix-its are offered even for a nonstandard enable_if.
+namespace nonstd {
+
+template <bool Condition, typename T = void>
+struct enable_if : std::enable_if<Condition, T> {};
+
+}
+
+template <typename T>
+typename nonstd::enable_if<some_type_trait<T>::value, void>::type nonstd_enable_if() {}
+// CHECK-MESSAGES: :[[@LINE-1]]:1: warning: use C++20 requires constraints instead of enable_if [modernize-use-constraints]
+// CHECK-FIXES: {{^}}void nonstd_enable_if() requires some_type_trait<T>::value {}{{$}}
+
+// But only if the nonstandard enable_if has the same signature as the standard one.
+namespace boost {
+
+template <typename Condition, typename T = void>
+struct enable_if : std::enable_if<Condition::value, T> {};
+
+}
+
+template <typename T>
+typename boost::enable_if<some_type_trait<T>, void>::type boost_enable_if() {}

clang-tools-extra/docs/ReleaseNotes.rst

clang-tools-extra/clang-tidy/modernize/UseConstraintsCheck.cpp

localspook · 2025-08-10T22:19:03Z

Latest commit fixes enable_if_t, it also causes this crash

vbvictor

LGTM, as a final sanity check, could we add tests with 1 param in enable_if and specialized function like template<> enable_if<true, int>::value foo()

localspook · 2025-08-12T17:46:51Z

The check right now skips non-dependent enable_if. Would you like the template<> enable_if<true, int>::value foo() test anyway?

vbvictor · 2025-08-12T18:24:23Z

The check right now skips non-dependent enable_if. Would you like the template<> enable_if<true, int>::value foo() test anyway?

If there isn't such a test right now, I'd say yes.
Generally, I think that every meaningful part in matchers should be tested, otherwise it should be removed as a patch "[NFC] simplify xxx check".

localspook · 2025-08-12T20:49:29Z

Looks like we have tests for non-dependent enable_if, but not for specializations, so I've gone and added them.

llvm-project/clang-tools-extra/test/clang-tidy/checkers/modernize/use-constraints.cpp

Lines 71 to 75 in 76f1c7a

    
           template <typename U> 
        
           std::enable_if_t<true, Obj> no_dependent_type(U) { 
        
             return Obj{}; 
        
           } 
        
           // FIXME - Support non-dependent enable_ifs. Low priority though...

[clang-tidy] Fix modernize-use-constraints crash on uses of nonstan…

728fc71

…dard `enable_if`s

localspook requested review from PiotrZSL, carlosgalvezp, EugeneZelenko, 5chmidti, vbvictor and HerrCai0907 August 10, 2025 19:35

llvmbot added clang-tools-extra clang-tidy labels Aug 10, 2025

localspook mentioned this pull request Aug 10, 2025

[clang-tidy] clang-tidy modernize-use-constraints causes a segfault when used against boost::futures::wait_for_all #152868

Closed

vbvictor reviewed Aug 10, 2025

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localspook added 2 commits August 10, 2025 13:22

Adjust wording

a189367

Remove check for zero template arguments, handle enable_if_t

3911696

Add asserts

3d273eb

vbvictor approved these changes Aug 12, 2025

View reviewed changes

Single argument form, specializations

f01c0fc

vbvictor approved these changes Aug 13, 2025

View reviewed changes

localspook merged commit 5b5a8cd into llvm:main Aug 23, 2025
10 checks passed

localspook deleted the enable-if-crash branch August 23, 2025 09:11

vbvictor mentioned this pull request Aug 25, 2025

[clang-tidy] Limit modernize-use-constraints to standard enable_if #155237

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[clang-tidy] Fix `modernize-use-constraints` crash on uses of nonstandard `enable_if`s #152938

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[clang-tidy] Fix modernize-use-constraints crash on uses of nonstandard enable_ifs #152938

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[clang-tidy] Fix `modernize-use-constraints` crash on uses of nonstandard `enable_if`s #152938

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