[clang-tidy] modernize-use-trailing-return-type: add an option to apply to void-returning functions as well

clang-tools-extra/clang-tidy/modernize/UseTrailingReturnTypeCheck.cpp

@@ -8,8 +8,11 @@
 
 #include "UseTrailingReturnTypeCheck.h"
 #include "clang/AST/ASTContext.h"
+#include "clang/AST/ASTTypeTraits.h"
+#include "clang/AST/DeclCXX.h"
 #include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Tooling/FixIt.h"
 #include "llvm/ADT/StringExtras.h"
@@ -457,6 +460,7 @@ static void keepSpecifiers(std::string &ReturnType, std::string &Auto,
 UseTrailingReturnTypeCheck::UseTrailingReturnTypeCheck(
     StringRef Name, ClangTidyContext *Context)
     : ClangTidyCheck(Name, Context),
+      WarnOnNonTrailingVoid(Options.get("WarnOnNonTrailingVoid", false)),
       TransformFunctions(Options.get("TransformFunctions", true)),
       TransformLambdas(Options.get("TransformLambdas", TransformLambda::All)) {
 
@@ -469,18 +473,23 @@ UseTrailingReturnTypeCheck::UseTrailingReturnTypeCheck(
 
 void UseTrailingReturnTypeCheck::storeOptions(
     ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "WarnOnNonTrailingVoid", WarnOnNonTrailingVoid);
   Options.store(Opts, "TransformFunctions", TransformFunctions);
   Options.store(Opts, "TransformLambdas", TransformLambdas);
 }
 
 void UseTrailingReturnTypeCheck::registerMatchers(MatchFinder *Finder) {
+  const auto HasNoWrittenReturnType =
+      anyOf(cxxConversionDecl(), cxxConstructorDecl(), cxxDestructorDecl());
+
   auto F =
-      functionDecl(
-          unless(anyOf(
-              hasTrailingReturn(), returns(voidType()), cxxConversionDecl(),
+      traverse(
+          TK_IgnoreUnlessSpelledInSource,
+          functionDecl(unless(anyOf(
+              hasTrailingReturn(), HasNoWrittenReturnType,
+              WarnOnNonTrailingVoid ? unless(anything()) : returns(voidType()),
               cxxMethodDecl(
-                  anyOf(isImplicit(),
-                        hasParent(cxxRecordDecl(hasParent(lambdaExpr()))))))))
+                  hasParent(cxxRecordDecl(hasParent(lambdaExpr()))))))))
           .bind("Func");
 
   if (TransformFunctions) {

clang-tools-extra/clang-tidy/modernize/UseTrailingReturnTypeCheck.h

@@ -40,6 +40,7 @@ class UseTrailingReturnTypeCheck : public ClangTidyCheck {
 
 private:
   Preprocessor *PP = nullptr;
+  const bool WarnOnNonTrailingVoid;
   const bool TransformFunctions;
   const TransformLambda TransformLambdas;
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -170,6 +170,11 @@ Changes in existing checks
   when the format string is converted to a different type by an implicit
   constructor call.
 
+- Improved :doc:`modernize-use-trailing-return-type
+  <clang-tidy/checks/modernize/use-trailing-return-type>` check by adding the
+  option `WarnOnNonTrailingVoid` that applies the check to ``void``-returning
+  functions that by default are excluded from this check.
+
 - Improved :doc:`performance-unnecessary-copy-initialization
   <clang-tidy/checks/performance/unnecessary-copy-initialization>` by printing
   the type of the diagnosed variable.

clang-tools-extra/docs/clang-tidy/checks/modernize/use-trailing-return-type.rst

@@ -27,6 +27,13 @@ transforms to:
   virtual auto f3() const && -> float = delete;
   auto lambda = []() -> void {};
 
+Options
+-------
+
+.. option:: WarnOnNonTrailingVoid
+
+  If the option is set to `true`, the check will apply even to function
+  signatures with return type ``void``. Default is `false`.
 
 Limitations
 -----------

clang-tools-extra/test/clang-tidy/checkers/modernize/use-trailing-return-type.cpp

@@ -1,4 +1,12 @@
-// RUN: %check_clang_tidy -std=c++14-or-later %s modernize-use-trailing-return-type %t -- -- -fdeclspec -fexceptions -DCOMMAND_LINE_INT=int
+// RUN: %check_clang_tidy                                                            \
+// RUN:   -std=c++14-or-later %s modernize-use-trailing-return-type %t --            \
+// RUN:   -- -fdeclspec -fexceptions -DCOMMAND_LINE_INT=int
+// RUN: %check_clang_tidy -check-suffixes=,WARN-ON-NONTRAILING-VOID                            \
+// RUN:   -std=c++14-or-later %s modernize-use-trailing-return-type %t --            \
+// RUN:   -config="{CheckOptions: {                                                  \
+// RUN:              modernize-use-trailing-return-type.WarnOnNonTrailingVoid: true, \
+// RUN:            }}"                                                               \
+// RUN:   -- -fdeclspec -fexceptions -DCOMMAND_LINE_INT=int
 
 namespace std {
     template <typename T>
@@ -566,6 +574,24 @@ ostream& operator<<(ostream& ostream, int i);
 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
 // CHECK-FIXES: {{^}}ostream& operator<<(ostream& ostream, int i);{{$}}
 
+//
+// WarnOnNonTrailingVoid option
+//
+
+void leadingVoid();
+// CHECK-MESSAGES-WARN-ON-NONTRAILING-VOID: :[[@LINE-1]]:6: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
+// CHECK-FIXES-WARN-ON-NONTRAILING-VOID: {{^}}auto leadingVoid() -> void;{{$}}
+void leadingVoid(int arg);
+// CHECK-MESSAGES-WARN-ON-NONTRAILING-VOID: :[[@LINE-1]]:6: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
+// CHECK-FIXES-WARN-ON-NONTRAILING-VOID: {{^}}auto leadingVoid(int arg) -> void;{{$}}
+void leadingVoid(int arg) { return; }
+// CHECK-MESSAGES-WARN-ON-NONTRAILING-VOID: :[[@LINE-1]]:6: warning: use a trailing return type for this function [modernize-use-trailing-return-type]
+// CHECK-FIXES-WARN-ON-NONTRAILING-VOID: {{^}}auto leadingVoid(int arg) -> void { return; }{{$}}
+
+auto trailingVoid() -> void;
+auto trailingVoid(int arg) -> void;
+auto trailingVoid(int arg) -> void { return; }
+
 //
 // Samples which do not trigger the check
 //
@@ -579,10 +605,6 @@ template <typename T> auto f(T t) -> int;
 
 auto ff();
 
-void c();
-void c(int arg);
-void c(int arg) { return; }
-
 struct D2 : B {
     D2();
     virtual ~D2();