[clang] [Clang][Sema] Diagnosis for constexpr constructor not initializing a union member (PR #81225)
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Thu Feb 8 20:32:53 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: None (mahtohappy)
<details>
<summary>Changes</summary>
For templates, isDependentContext() is true, that's why the previous if check was failing.
Here, we traverse the RD and upon finding a Union declaration we check if at least one member of the union is initialized.
If not, it produces a diagnosis for it.
Fix #<!-- -->46689
---
Full diff: https://github.com/llvm/llvm-project/pull/81225.diff
4 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+3-2)
- (modified) clang/lib/Sema/SemaDeclCXX.cpp (+37-11)
- (modified) clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp (+4-2)
- (added) clang/test/SemaCXX/constexpr-union-temp-ctor-cxx.cpp (+27)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 32440ee64e3ebe..0072495354b8eb 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -149,9 +149,10 @@ Improvements to Clang's diagnostics
prints.
- Clang now diagnoses member template declarations with multiple declarators.
+- Clang now diagnoses use of the ``template`` keyword after declarative nested name specifiers.
-- Clang now diagnoses use of the ``template`` keyword after declarative nested
- name specifiers.
+- Clang now diagnoses constexpr constructor for not initializing atleast one member of union
+- Fixes(`#46689 Constexpr constructor not initializing a union member is not diagnosed`)
- The ``-Wshorten-64-to-32`` diagnostic is now grouped under ``-Wimplicit-int-conversion`` instead
of ``-Wconversion``. Fixes `#69444 <https://github.com/llvm/llvm-project/issues/69444>`_.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index fea8c5036c80b1..f6c7410e3be92a 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1795,6 +1795,12 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
Stmt *Body,
Sema::CheckConstexprKind Kind);
+static bool
+checkUnionConstructorIntializer(Sema &SemaRef, const FunctionDecl *Dcl,
+ const CXXConstructorDecl *Constructor,
+ const CXXRecordDecl *RD,
+ Sema::CheckConstexprKind Kind);
+
// Check whether a function declaration satisfies the requirements of a
// constexpr function definition or a constexpr constructor definition. If so,
// return true. If not, produce appropriate diagnostics (unless asked not to by
@@ -2343,17 +2349,9 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
// - if the class is a union having variant members, exactly one of them
// shall be initialized;
if (RD->isUnion()) {
- if (Constructor->getNumCtorInitializers() == 0 &&
- RD->hasVariantMembers()) {
- if (Kind == Sema::CheckConstexprKind::Diagnose) {
- SemaRef.Diag(
- Dcl->getLocation(),
- SemaRef.getLangOpts().CPlusPlus20
- ? diag::warn_cxx17_compat_constexpr_union_ctor_no_init
- : diag::ext_constexpr_union_ctor_no_init);
- } else if (!SemaRef.getLangOpts().CPlusPlus20) {
- return false;
- }
+ if (checkUnionConstructorIntializer(SemaRef, Dcl, Constructor, RD,
+ Kind)) {
+ return false;
}
} else if (!Constructor->isDependentContext() &&
!Constructor->isDelegatingConstructor()) {
@@ -2393,6 +2391,17 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
Kind))
return false;
}
+ } else if (!Constructor->isDelegatingConstructor()) {
+ for (const Decl *Decls : RD->decls()) {
+ if (const auto *Inner = dyn_cast<CXXRecordDecl>(Decls)) {
+ if (Inner->isUnion()) {
+ if (checkUnionConstructorIntializer(SemaRef, Dcl, Constructor,
+ Inner, Kind)) {
+ return true;
+ }
+ }
+ }
+ }
}
} else {
if (ReturnStmts.empty()) {
@@ -2471,6 +2480,23 @@ static bool CheckConstexprFunctionBody(Sema &SemaRef, const FunctionDecl *Dcl,
return true;
}
+static bool
+checkUnionConstructorIntializer(Sema &SemaRef, const FunctionDecl *Dcl,
+ const CXXConstructorDecl *Constructor,
+ const CXXRecordDecl *RD,
+ Sema::CheckConstexprKind Kind) {
+ if (Constructor->getNumCtorInitializers() == 0 && RD->hasVariantMembers()) {
+ if (Kind == Sema::CheckConstexprKind::Diagnose) {
+ SemaRef.Diag(Dcl->getLocation(),
+ SemaRef.getLangOpts().CPlusPlus20
+ ? diag::warn_cxx17_compat_constexpr_union_ctor_no_init
+ : diag::ext_constexpr_union_ctor_no_init);
+ } else if (!SemaRef.getLangOpts().CPlusPlus20) {
+ return true;
+ }
+ }
+ return false;
+}
bool Sema::CheckImmediateEscalatingFunctionDefinition(
FunctionDecl *FD, const sema::FunctionScopeInfo *FSI) {
if (!getLangOpts().CPlusPlus20 || !FD->isImmediateEscalating())
diff --git a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
index f1f677ebfcd341..a4434d1c35943f 100644
--- a/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
+++ b/clang/test/CXX/dcl.dcl/dcl.spec/dcl.constexpr/p4.cpp
@@ -222,8 +222,10 @@ struct TemplateInit {
T g;
T h;
};
- // FIXME: This is ill-formed (no diagnostic required). We should diagnose it.
- constexpr TemplateInit() {} // desired-error {{must initialize all members}}
+ constexpr TemplateInit() {}
+#ifndef CXX2A
+ // expected-error at -2 {{constexpr union constructor that does not initialize any member is a C++20 extension}}
+#endif
};
template<typename T> struct TemplateInit2 {
Literal l;
diff --git a/clang/test/SemaCXX/constexpr-union-temp-ctor-cxx.cpp b/clang/test/SemaCXX/constexpr-union-temp-ctor-cxx.cpp
new file mode 100644
index 00000000000000..51d5e1d8cf9341
--- /dev/null
+++ b/clang/test/SemaCXX/constexpr-union-temp-ctor-cxx.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -std=c++14 -verify -fcxx-exceptions -Werror=c++14-extensions -Werror=c++20-extensions %s
+
+template <class> struct C {
+ union {
+ int i;
+ };
+ constexpr C() {} // expected-error {{constexpr union constructor that does not initialize any member is a C++20 extension}}
+};
+constexpr C<int> c;
+
+template <class> class D {
+ union {
+ int i;
+ };
+public:
+ constexpr D() {} // expected-error {{constexpr union constructor that does not initialize any member is a C++20 extension}}
+};
+constexpr D<int> d;
+
+template<typename T>
+struct Foo {
+ union {
+ int i;
+ };
+ constexpr Foo(int a): i(a){}
+};
+constexpr Foo<int> f(5);
``````````
</details>
https://github.com/llvm/llvm-project/pull/81225
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