readability-const-return-type: don't diagnose a template function returning T, even if sometimes instantiated with e.g. T = const int.

[suertreus]

Summary

It's not really a readability problem since there's no const to read at the declaration site, and returning std::remove_const_t<T> instead usually only hurts readability.

[ymandel]

Thanks!

[suertreus]

Thanks for reviewing.

I don't have commit access; can someone who does please do the thing?

[ymandel]

Sure, please ping me if you don't see a commit by EOD

[carlosgalvezp]

In D140434#4053053, @suertreus wrote:

Thanks for reviewing.

I don't have commit access; can someone who does please do the thing?

@suertreus I can help you land the patch, what user name and email should I use for attribution?

[ymandel]

In D140434#4071823, @carlosgalvezp wrote:

In D140434#4053053, @suertreus wrote:

Thanks for reviewing.

I don't have commit access; can someone who does please do the thing?

@suertreus I can help you land the patch, what user name and email should I use for attribution?

Sorry for the delay -- I'm doing the commit now (just running tests first)

[suertreus]

Andy Getzendanner <[e-mail]> please, and thanks!

[carlosgalvezp]

In D140434#4073212, @ymandel wrote:

In D140434#4071823, @carlosgalvezp wrote:

In D140434#4053053, @suertreus wrote:

Thanks for reviewing.

I don't have commit access; can someone who does please do the thing?

@suertreus I can help you land the patch, what user name and email should I use for attribution?

Sorry for the delay -- I'm doing the commit now (just running tests first)

Sounds good, I'll leave you to it :) Let me know otherwise if you need help!

clang-tools-extra/clang-tidy/readability/ConstReturnTypeCheck.cpp

 
 void ConstReturnTypeCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "IgnoreMacros", IgnoreMacros);
 }
 
 void ConstReturnTypeCheck::registerMatchers(MatchFinder *Finder) {
   // Find all function definitions for which the return types are `const`
   // qualified, ignoring decltype types.
-  auto NonLocalConstType = qualType(
-      unless(isLocalConstQualified()),
-      anyOf(decltypeType(), autoType(), isTypeOfType(), isTypeOfExprType()));
+  auto NonLocalConstType =
+      qualType(unless(isLocalConstQualified()),
+               anyOf(decltypeType(), autoType(), isTypeOfType(),
+                     isTypeOfExprType(), substTemplateTypeParmType()));
   Finder->addMatcher(
       functionDecl(
           returns(allOf(isConstQualified(), unless(NonLocalConstType))),
           anyOf(isDefinition(), cxxMethodDecl(isPure())),
           // Overridden functions are not actionable.
           unless(cxxMethodDecl(isOverride())))
           .bind("func"),
       this);

clang-tools-extra/test/clang-tidy/checkers/readability/const-return-type.cpp

 __typeof__(n17i) n20() {
   return 20;
 }
 
 // Don't warn about `__typeof__(type)` types
 __typeof__(const int) n21() {
   return 21;
 }
+
+template <typename T>
+struct n25 {
+  T foo() const { return 2; }
+};
+template struct n25<const int>;
+
+template <typename T>
+struct p41 {
+  const T foo() const { return 2; }
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: return type 'const
+  // CHECK-MESSAGES: [[@LINE-2]]:3: warning: return type 'const
+  // CHECK-FIXES: T foo() const { return 2; }
+};
+template struct p41<int>;