[PATCH] D119470: [clang-tidy] Don't check decltype return types in `readability-const-return-type`

[Evgeny Shulgin via Phabricator via cfe-commits]

Izaron updated this revision to Diff 416035.
Izaron added a comment.
Herald added a project: All.

Don't warn on non-toplevel-const TypeOfType


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119470/new/

https://reviews.llvm.org/D119470

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


Index: clang-tools-extra/test/clang-tidy/checkers/readability-const-return-type.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/readability-const-return-type.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/readability-const-return-type.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy %s readability-const-return-type %t
+// RUN: %check_clang_tidy -std=c++14 %s readability-const-return-type %t
 
 //  p# = positive test
 //  n# = negative test
@@ -285,3 +285,40 @@
   // CHECK-MESSAGES: [[@LINE-1]]:3: warning: return type 'const int' is 'const'-qualified at the top level, which may reduce code readability without improving const correctness
   // CHECK-NOT-FIXES: int getC() { return 1; }
 };
+
+// Don't warn about const auto types, because it may be impossible to make them non-const
+// without a significant semantics change. Since `auto` drops cv-qualifiers,
+// tests check `decltype(auto)`.
+decltype(auto) n16() {
+  static const int i = 42;
+  return i;
+}
+
+// Don't warn about `decltype(<expr>)` types
+const int n17i = 1;
+decltype(n17i) n17() {
+  return 17;
+}
+
+// Do warn when on decltype types with the local const qualifier
+// `const decltype(auto)` won't compile, so check only `const decltype(<expr>)`
+const decltype(n17i) n18() {
+  // CHECK-MESSAGES: [[@LINE-1]]:1: warning: return type 'const decltype(n17i)
+  // CHECK-FIXES: decltype(n17i) n18() {
+  return 18;
+}
+
+// `volatile` modifier doesn't affect the checker
+volatile decltype(n17i) n19() {
+  return 19;
+}
+
+// Don't warn about `__typeof__(<expr>)` types
+__typeof__(n17i) n20() {
+  return 20;
+}
+
+// Don't warn about `__typeof__(type)` types
+__typeof__(const int) n21() {
+  return 21;
+}
Index: clang-tools-extra/clang-tidy/readability/ConstReturnTypeCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/readability/ConstReturnTypeCheck.cpp
+++ clang-tools-extra/clang-tidy/readability/ConstReturnTypeCheck.cpp
@@ -53,6 +53,18 @@
 
 namespace {
 
+AST_MATCHER(QualType, isLocalConstQualified) {
+  return Node.isLocalConstQualified();
+}
+
+AST_MATCHER(QualType, isTypeOfType) {
+  return isa<TypeOfType>(Node.getTypePtr());
+}
+
+AST_MATCHER(QualType, isTypeOfExprType) {
+  return isa<TypeOfExprType>(Node.getTypePtr());
+}
+
 struct CheckResult {
   // Source range of the relevant `const` token in the definition being checked.
   CharSourceRange ConstRange;
@@ -95,10 +107,14 @@
 
 void ConstReturnTypeCheck::registerMatchers(MatchFinder *Finder) {
   // Find all function definitions for which the return types are `const`
-  // qualified.
+  // qualified, ignoring decltype types.
+  auto NonLocalConstType = qualType(
+      unless(isLocalConstQualified()),
+      anyOf(decltypeType(), autoType(), isTypeOfType(), isTypeOfExprType()));
   Finder->addMatcher(
-      functionDecl(returns(isConstQualified()),
-                   anyOf(isDefinition(), cxxMethodDecl(isPure())))
+      functionDecl(
+          returns(allOf(isConstQualified(), unless(NonLocalConstType))),
+          anyOf(isDefinition(), cxxMethodDecl(isPure())))
           .bind("func"),
       this);
 }


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