[Sema] Diagnose by-value copy constructors in template instantiations by Megan0704-1 · Pull Request #130866 · llvm/llvm-project (original) (raw)
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Fixes #80963
This PR ensures Clang diagnoses by-value copy constructors in implicitly instantiated class templates (e.g., A<int, int>(A<int, int>)), per [class.copy.ctor].
Changes:
- Remove
TSK_ImplicitInstantiationcheck inSemaDeclCXX.cpp. - Add
!isFunctionTemplateSpecialization()to skip templated constructors. - Add regression tests.
Fixes llvm#80963
Previously, Clang skipped diagnosing a constructor if it was implicitly instantiated from a template class (TSK_ImplicitInstantiation). This allowed ill-formed “copy” constructors taking the class by value (e.g. A(A)) to slip through without a diagnostic.
However, the C++ standard mandates that copy constructors must take their class type parameter by reference (e.g., A(const A&)). Furthermore, a constructor template that would form a copy-by-value signature is not treated as a copy constructor and should never be chosen for copying.
This patch replaces the check on TSK_ImplicitInstantiation with a check to see if the constructor is a function template specialization (i.e., isFunctionTemplateSpecialization()). That ensures proper diagnosis of non-template copy-by-value constructors, while still allowing valid template constructors that might appear to have a copy-like signature but should be SFINAEd out or simply not selected as a copy constructor.
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Clang issues not falling into any other category
Language frontend issues, e.g. anything involving "Sema"
labels
@llvm/pr-subscribers-clang
Author: Kuo, Mei-Chun (Megan0704-1)
Changes
Fixes #80963
This PR ensures Clang diagnoses by-value copy constructors in implicitly instantiated class templates (e.g., A<int, int>(A<int, int>)), per [class.copy.ctor].
Changes:
- Remove
TSK_ImplicitInstantiationcheck inSemaDeclCXX.cpp. - Add
!isFunctionTemplateSpecialization()to skip templated constructors. - Add regression tests.
Full diff: https://github.com/llvm/llvm-project/pull/130866.diff
2 Files Affected:
- (modified) clang/lib/Sema/SemaDeclCXX.cpp (+2-2)
- (added) clang/test/SemaCXX/copy-ctor-template.cpp (+22)
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp index 96aac7871db1e..1c62a551ee732 100644 --- a/clang/lib/Sema/SemaDeclCXX.cpp +++ b/clang/lib/Sema/SemaDeclCXX.cpp @@ -10921,8 +10921,8 @@ void Sema::CheckConstructor(CXXConstructorDecl *Constructor) { // parameters have default arguments. if (!Constructor->isInvalidDecl() && Constructor->hasOneParamOrDefaultArgs() &&
Constructor->getTemplateSpecializationKind() !=TSK_ImplicitInstantiation) {
!Constructor->isFunctionTemplateSpecialization()
QualType ParamType = Constructor->getParamDecl(0)->getType(); QualType ClassTy = Context.getTagDeclType(ClassDecl); if (Context.getCanonicalType(ParamType).getUnqualifiedType() == ClassTy) { diff --git a/clang/test/SemaCXX/copy-ctor-template.cpp b/clang/test/SemaCXX/copy-ctor-template.cpp new file mode 100644 index 0000000000000..a46a167038cf7 --- /dev/null +++ b/clang/test/SemaCXX/copy-ctor-template.cpp @@ -0,0 +1,22 @@ +// RUN: %clang_cc1 -fsyntax-only -verify %s) {- +template<class T, class V> +struct A{
- A();
- A(A&);
- A(A<V, T>); // expected-error{{copy constructor must pass its first argument by reference}}
+}; + +void f() {
- A<int, int> a = A<int, int>(); // expected-note{{in instantiation of template class 'A<int, int>'}}
+} + +template<class T, class V> +struct B{
- B();
- template B(U); // No error (templated constructor)
+}; + +void g() {
- B<int, int> b = B<int, int>(); // should use implicit copy constructor
+}
@erichkeane, @shafik
Could you please take a look and let me know if it looks good to you? Thank you very much!
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Thanks for working on this
Can you add a changelog entry in clang/docs/ReleaseNotes.rst (in the bug fixes to c++ section)?
Thanks
| void g() { |
| B<int, int> b = B<int, int>(); // should use implicit copy constructor |
| } |
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Thanks for the review! I’ll add tests for the A<int, double> case and update the PR shortly.
Thanks for your feedback and review!! I’ve updated the changelog and the test file to include the rvalue-to-lvalue case and converting constructor scenario. Please let me know if there’s anything else!
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LGTM. Thanks for fixing this issue!
Will you need me to merge this for you?
Thank you for reviewing and approving the PR!
Yes, please merge it for me. Thanks again for all your help!
Adjust the test to account for new diagnostics emitted when a class template constructor takes the class by value after instantiation.
- Add expected-error annotations to lines 142, 159, 172 (invalid by-value constructors when T = U).
- Add expected-note annotations to lines 147, 164, 176 (template instantiation points).
- Remove expected-error from line 76 (valid template specialization).
@cor3ntin
Thank you for flagging the test failures!
I’ve investigated them, and here’s what I found:
Failed Tests in constructor-template.cpp:
- The failures occurred because the test wasn’t annotated to expect the new diagnostics introduced by the fix (e.g., A<int, int> instantiations now emit errors for invalid by-value copy constructors).
Fix it by updating the test to:
- Add expected-error to lines 142, 159, 172 (invalid by-value constructors when T = U).
- Add expected-note to lines 147, 164, 176 (template instantiation points).
- Remove an incorrect expected-error from line 76 (valid template specialization).
Please Let me know if further adjustments are needed~
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⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️
You can test this locally with the following command:
git-clang-format --diff c2ed840ed94d3412c7c0bdd9ed84cac6fe0afb57 790d151975c9ce4f5f823484d100d9460077b971 --extensions cpp -- clang/test/SemaCXX/copy-ctor-template.cpp clang/lib/Sema/SemaDeclCXX.cpp clang/test/SemaTemplate/constructor-template.cpp
View the diff from clang-format here.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp index 1c62a551ee..00b4006b5e 100644 --- a/clang/lib/Sema/SemaDeclCXX.cpp +++ b/clang/lib/Sema/SemaDeclCXX.cpp @@ -10921,8 +10921,7 @@ void Sema::CheckConstructor(CXXConstructorDecl *Constructor) { // parameters have default arguments. if (!Constructor->isInvalidDecl() && Constructor->hasOneParamOrDefaultArgs() &&
!Constructor->isFunctionTemplateSpecialization()) {
QualType ParamType = Constructor->getParamDecl(0)->getType(); QualType ClassTy = Context.getTagDeclType(ClassDecl); if (Context.getCanonicalType(ParamType).getUnqualifiedType() == ClassTy) {!Constructor->isFunctionTemplateSpecialization()) {
| Constructor->getTemplateSpecializationKind() != |
|---|
| TSK_ImplicitInstantiation) { |
| !Constructor->isFunctionTemplateSpecialization() |
| ) { |
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Did you run clang-format on this? I am surprised it would leave the ) on the line like that but maybe I am off.
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Thank you for catching this, and I am so sorry for the oversight.
I forgot to run clang-format before merging.
Should I submitt a follow-up PR to fix the formatting issues?
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I missed it too, sorry.
yes, feel free to submit a new pr. thanks
cor3ntin pushed a commit that referenced this pull request
This PR fixes formatting issues in constructor-template.cpp introduced
in #130866.
Changes:
- Ran
clang-formatto adhere to LLVM style guidelines. - No functional changes.
frederik-h pushed a commit to frederik-h/llvm-project that referenced this pull request
Fixes llvm#80963
This PR ensures Clang diagnoses by-value copy constructors in implicitly
instantiated class templates (e.g., A<int, int>(A<int, int>)), per
[class.copy.ctor].
Changes:
- Remove
TSK_ImplicitInstantiationcheck inSemaDeclCXX.cpp. - Add
!isFunctionTemplateSpecialization()to skip templated constructors. - Add regression tests.
frederik-h pushed a commit to frederik-h/llvm-project that referenced this pull request
This PR fixes formatting issues in constructor-template.cpp introduced
in llvm#130866.
Changes:
- Ran
clang-formatto adhere to LLVM style guidelines. - No functional changes.
This error is produced for the following code:
template class SetView { SetView(SetView<std::remove_const_t> other_view) requires(!std::same_as<KeyT, std::remove_const_t>); };
... which is never an eligible copy constructor. Is that intended? If this is in line with the language rules, perhaps we should file a core issue.
[Edit: I've mailed the core reflector.]
Labels
Language frontend issues, e.g. anything involving "Sema"
Clang issues not falling into any other category