[clang] Warning for incorrect useof 'pure' attribute (PR #78200)

[Erich Keane via cfe-commits]

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@@ -11792,6 +11792,32 @@ static bool CheckMultiVersionFunction(Sema &S, FunctionDecl *NewFD,
                                          OldDecl, Previous);
 }
 
+static void CheckFunctionDeclarationAttributesUsage(Sema &S,
+                                                    FunctionDecl *NewFD) {
+  const bool is_pure = NewFD->hasAttr<PureAttr>();
+  const bool is_const = NewFD->hasAttr<ConstAttr>();
+
+  if (is_pure && is_const) {
+    S.Diag(NewFD->getLocation(), diag::warn_const_attr_with_pure_attr);
+    NewFD->dropAttr<PureAttr>();
+  }
+  if (is_pure || is_const) {
+    if (isa<CXXConstructorDecl>(NewFD)) {
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erichkeane wrote:

>(not counting placement new)

Thats a big 'not counting' there...

`A a = A(args...);`

That isn't calling the constructor, that is effectively 'constructing an object, then copying it to the LHS (though we omit the copy)'.

`A a{args...};`  is also valid, which shows that it isn't the same.




https://github.com/llvm/llvm-project/pull/78200