[PATCH] D26207: [ClangTidy - performance-unnecessary-value-param] Only add "const" when current parameter is not already const qualified

Aaron Ballman via cfe-commits cfe-commits at lists.llvm.org
Wed Nov 2 09:42:38 PDT 2016

aaron.ballman added inline comments.

Comment at: clang-tidy/performance/UnnecessaryValueParamCheck.cpp:131
-    if (!IsConstQualified)
+    if (!CurrentParam.getType().getCanonicalType().isConstQualified())
       Diag << utils::fixit::changeVarDeclToConst(CurrentParam);
You should add a comment here explaining why you need something more complex than `IsConstQualified`.

Comment at: test/clang-tidy/performance-unnecessary-value-param.cpp:242
+// Case where parameter in declaration is already const-qualified but not in
+// implementation. Make sure a second 'const' is not added to the declaration.
+void PositiveConstDeclaration(const ExpensiveToCopyType A);
flx wrote:
> aaron.ballman wrote:
> > This comment doesn't really match the test cases. The original code has two *different* declarations (only one of which is a definition), not one declaration and one redeclaration with the definition.
> > 
> > I think what is really happening is that it is adding the `&` qualifier to the first declaration, and adding the `const` and `&` qualifiers to the second declaration, and the result is that you get harmonization. But it brings up a question to me; what happens with:
> > ```
> > void f1(ExpensiveToCopyType A) {
> > }
> > 
> > void f1(const ExpensiveToCopyType A) {
> > 
> > }
> > ```
> > Does the fix-it try to create two definitions of the same function?
> Good catch. I added the reverse case as well and modified the check slightly to make that case work as well.
Can you add a test like this as well?
void f1(ExpensiveToCopyType A); // Declared, not defined

void f1(const ExpensiveToCopyType A) {}
void f1(const ExpensiveToCopyType &A) {}
I'm trying to make sure this check does not suggest a fixit that breaks existing code because of overload sets. I would expect a diagnostic for the first two declarations, but no fixit suggestion for `void f1(const ExpensiveToCopyType A)` because that would result in an ambiguous function definition.



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