Add new flag -Wreturn-mismatch (#82872)

This pull request fixes #72116 where a new flag is introduced for
compatibility with GCC 14, the functionality of -Wreturn-type is
modified to split some of its behaviors into -Wreturn-mismatch

Fixes #72116

Author: 11happy

clang/docs/ReleaseNotes.rst

@@ -183,6 +183,9 @@ Deprecated Compiler Flags
 
 Modified Compiler Flags
 -----------------------
+- Added a new diagnostic flag ``-Wreturn-mismatch`` which is grouped under
+  ``-Wreturn-type``, and moved some of the diagnostics previously controlled by
+  ``-Wreturn-type`` under this new flag. Fixes #GH72116.
 
 Removed Compiler Flags
 -------------------------

clang/include/clang/Basic/DiagnosticGroups.td

@@ -617,7 +617,9 @@ def GNURedeclaredEnum : DiagGroup<"gnu-redeclared-enum">;
 def RedundantMove : DiagGroup<"redundant-move">;
 def Register : DiagGroup<"register", [DeprecatedRegister]>;
 def ReturnTypeCLinkage : DiagGroup<"return-type-c-linkage">;
-def ReturnType : DiagGroup<"return-type", [ReturnTypeCLinkage]>;
+def ReturnMismatch : DiagGroup<"return-mismatch">;
+def ReturnType : DiagGroup<"return-type", [ReturnTypeCLinkage, ReturnMismatch]>;
+
 def BindToTemporaryCopy : DiagGroup<"bind-to-temporary-copy",
                                     [CXX98CompatBindToTemporaryCopy]>;
 def SelfAssignmentField : DiagGroup<"self-assign-field">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10248,14 +10248,14 @@ def warn_second_parameter_to_va_arg_never_compatible : Warning<
 
 def warn_return_missing_expr : Warning<
   "non-void %select{function|method}1 %0 should return a value">, DefaultError,
-  InGroup<ReturnType>;
+  InGroup<ReturnMismatch>;
 def ext_return_missing_expr : ExtWarn<
   "non-void %select{function|method}1 %0 should return a value">, DefaultError,
-  InGroup<ReturnType>;
+  InGroup<ReturnMismatch>;
 def ext_return_has_expr : ExtWarn<
   "%select{void function|void method|constructor|destructor}1 %0 "
   "should not return a value">,
-  DefaultError, InGroup<ReturnType>;
+  DefaultError, InGroup<ReturnMismatch>;
 def ext_return_has_void_expr : Extension<
   "void %select{function|method|block}1 %0 should not return void expression">;
 def err_return_init_list : Error<

clang/test/Misc/warning-wall.c

@@ -44,6 +44,7 @@ CHECK-NEXT:      -Wreorder-ctor
 CHECK-NEXT:      -Wreorder-init-list
 CHECK-NEXT:    -Wreturn-type
 CHECK-NEXT:      -Wreturn-type-c-linkage
+CHECK-NEXT:      -Wreturn-mismatch
 CHECK-NEXT:    -Wself-assign
 CHECK-NEXT:      -Wself-assign-overloaded
 CHECK-NEXT:      -Wself-assign-field

clang/test/Sema/return-type-mismatch.c

@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -Wreturn-type -Wno-return-mismatch -fsyntax-only -verify=return-type %s
+// RUN: %clang_cc1 -Wno-return-type -Wreturn-mismatch -fsyntax-only -verify=return-mismatch %s
+
+int foo(void) __attribute__((noreturn));
+int bar(void);
+
+void test1(void) {
+  return 1; // return-mismatch-warning{{void function 'test1' should not return a value}}
+}
+
+int test2(void) { 
+    return; // return-mismatch-warning{{non-void function 'test2' should return a value}}
+} 
+
+int test3(void) { 
+    // return-type-warning@+1 {{non-void function does not return a value}}
+} 
+
+int test4(void) {
+    (void)(bar() || foo()); // return-type-warning@+1 {{non-void function does not return a value in all control paths}}
+} 
+
+void test5(void) {
+} // no-warning
+
+int test6(void) {
+  return 0; // no-warning
+}
+
+int test7(void) {
+  foo(); // no warning
+}
+
+int test8(void) {
+  bar(); // return-type-warning@+1 {{non-void function does not return a value}}
+}