[Diagnostics] Try to improve warning message for -Wreturn-type

Summary: I agree with https://easyaspi314.github.io/gcc-vs-clang.html?fbclid=IwAR1VA0qxiWVUusOQUv5z7JESS7ZpeJy-UqAI5mnJscofGLqXcqeErIUB2gU, current warning message is not very good. We should try to improve it..

Reviewers: rsmith, aaron.ballman, easyaspi314

Reviewed By: aaron.ballman

Subscribers: arphaman, Quuxplusone, mehdi_amini, hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D69762

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -575,21 +575,22 @@ def err_thread_non_global : Error<
 def err_thread_unsupported : Error<
   "thread-local storage is not supported for the current target">;
 
+// FIXME: Combine fallout warnings to just one warning.
 def warn_maybe_falloff_nonvoid_function : Warning<
-  "control may reach end of non-void function">,
+  "non-void function does not return a value in all control paths">,
   InGroup<ReturnType>;
 def warn_falloff_nonvoid_function : Warning<
-  "control reaches end of non-void function">,
+  "non-void function does not return a value">,
   InGroup<ReturnType>;
 def err_maybe_falloff_nonvoid_block : Error<
-  "control may reach end of non-void block">;
+  "non-void block does not return a value in all control paths">;
 def err_falloff_nonvoid_block : Error<
-  "control reaches end of non-void block">;
+  "non-void block does not return a value">;
 def warn_maybe_falloff_nonvoid_coroutine : Warning<
-  "control may reach end of coroutine; which is undefined behavior because the promise type %0 does not declare 'return_void()'">,
+  "non-void coroutine does not return a value in all control paths">,
   InGroup<ReturnType>;
 def warn_falloff_nonvoid_coroutine : Warning<
-  "control reaches end of coroutine; which is undefined behavior because the promise type %0 does not declare 'return_void()'">,
+  "non-void coroutine does not return a value">,
   InGroup<ReturnType>;
 def warn_suggest_noreturn_function : Warning<
   "%select{function|method}0 %1 could be declared with attribute 'noreturn'">,
@@ -6858,10 +6859,10 @@ let CategoryName = "Lambda Issue" in {
   def err_noreturn_lambda_has_return_expr : Error<
     "lambda declared 'noreturn' should not return">;
   def warn_maybe_falloff_nonvoid_lambda : Warning<
-    "control may reach end of non-void lambda">,
+    "non-void lambda does not return a value in all control paths">,
     InGroup<ReturnType>;
   def warn_falloff_nonvoid_lambda : Warning<
-    "control reaches end of non-void lambda">,
+    "non-void lambda does not return a value">,
     InGroup<ReturnType>;
   def err_access_lambda_capture : Error<
     // The ERRORs represent other special members that aren't constructors, in

clang/test/Analysis/const-method-call.cpp

@@ -235,7 +235,7 @@ public:
   void constMemberFunction() const;
 };
 
-HasConstMemberFunction hasNoReturn() { } // expected-warning {{control reaches end of non-void function}}
+HasConstMemberFunction hasNoReturn() { } // expected-warning {{non-void function does not return a value}}
 
 void testUnknownWithConstMemberFunction() {
   hasNoReturn().constMemberFunction();

clang/test/Analysis/structured_bindings.cpp

@@ -5,5 +5,5 @@ int foo() {
     auto[a] = s{1}; // FIXME: proper modelling
     if (a) {
     }
-} // expected-warning{{control reaches end of non-void function}}
+} // expected-warning{{non-void function does not return a value}}
 

clang/test/CXX/expr/expr.prim/expr.prim.lambda/p5.cpp

@@ -3,7 +3,7 @@
 // An attribute-specifier-seq in a lambda-declarator appertains to the
 // type of the corresponding function call operator.
 void test_attributes() {
-  auto nrl = [](int x) -> int { if (x > 0) return x; }; // expected-warning{{control may reach end of non-void lambda}}
+  auto nrl = [](int x) -> int { if (x > 0) return x; }; // expected-warning{{on-void lambda does not return a value in all control paths}}
 
   // FIXME: GCC accepts the [[gnu::noreturn]] attribute here.
   auto nrl2 = []() [[gnu::noreturn]] { return; }; // expected-warning{{attribute 'noreturn' ignored}}

clang/test/CXX/expr/expr.prim/expr.prim.lambda/p7.cpp

@@ -2,7 +2,7 @@
 
 // Check that analysis-based warnings work in lambda bodies.
 void analysis_based_warnings() {
-  (void)[]() -> int { }; // expected-warning{{control reaches end of non-void lambda}}
+  (void)[]() -> int { }; // expected-warning{{non-void lambda does not return a value}}
 }
 
 // Check that we get the right types of captured variables (the

clang/test/Driver/cc-log-diagnostics.c

@@ -29,7 +29,7 @@ int f0() {}
 // CHECK:       <key>column</key>
 // CHECK:       <integer>11</integer>
 // CHECK:       <key>message</key>
-// CHECK:       <string>control reaches end of non-void function</string>
+// CHECK:       <string>non-void function does not return a value</string>
 // CHECK:     </dict>
 // CHECK:   </array>
 // CHECK: </dict>

clang/test/Frontend/absolute-paths.c

@@ -7,11 +7,11 @@
 // directory in the path.
 // NORMAL: SystemHeaderPrefix
 // ABSOLUTE-NOT: SystemHeaderPrefix
-// CHECK: warning: control reaches end of non-void function
+// CHECK: warning: non-void function does not return a value
 
 
 // For files which don't exist, just print the filename.
 #line 123 "non-existant.c"
 int g() {}
-// NORMAL: non-existant.c:123:10: warning: control reaches end of non-void function
-// ABSOLUTE: non-existant.c:123:10: warning: control reaches end of non-void function
+// NORMAL: non-existant.c:123:10: warning: non-void function does not return a value
+// ABSOLUTE: non-existant.c:123:10: warning: non-void function does not return a value

clang/test/Index/warning-flags.c

@@ -9,10 +9,10 @@ int *bar(float *f) { return f; }
 // RUN: c-index-test -test-load-source-reparse 5 all -w %s 2>&1 | FileCheck -check-prefix=NOWARNINGS %s
 // RUN: c-index-test -test-load-source all -w -O4 %s 2>&1 | FileCheck -check-prefix=NOWARNINGS %s
 
-// CHECK-BOTH-WARNINGS: warning: control reaches end of non-void function
+// CHECK-BOTH-WARNINGS: warning: non-void function does not return a value
 // CHECK-BOTH-WARNINGS: warning: incompatible pointer types returning 'float *' from a function with result type 'int *'
 
-// CHECK-SECOND-WARNING-NOT:control reaches end of non-void
+// CHECK-SECOND-WARNING-NOT:non-void function does not return a value
 // CHECK-SECOND-WARNING: warning: incompatible pointer types returning 'float *' from a function with result type 'int *'
 
 // NOWARNINGS-NOT: warning:

clang/test/Misc/serialized-diags-stable.c

@@ -5,7 +5,7 @@
 // RUN: c-index-test -read-diagnostics %S/Inputs/serialized-diags-stable.dia 2>&1 | FileCheck %s
 
 int foo() {
-  // CHECK: serialized-diags-stable.c:[[@LINE+2]]:1: warning: control reaches end of non-void function [-Wreturn-type] [Semantic Issue]
+  // CHECK: serialized-diags-stable.c:[[@LINE+2]]:1: warning: non-void function does not return a value [-Wreturn-type] [Semantic Issue]
   // CHECK-NEXT: Number FIXITs = 0
 }
 

clang/test/Modules/redecl-merge.m

@@ -12,11 +12,11 @@ typedef struct my_struct_type *my_struct_ref;
 
 int *call_eventually_noreturn(void) {
   eventually_noreturn();
-} // expected-warning{{control reaches end of non-void function}}
+} // expected-warning{{non-void function does not return a value}}
 
 int *call_eventually_noreturn2(void) {
   eventually_noreturn2();
-} // expected-warning{{control reaches end of non-void function}}
+} // expected-warning{{non-void function does not return a value}}
 
 @import redecl_merge_right;
 

clang/test/PCH/late-parsed-instantiations.cpp

@@ -20,8 +20,8 @@ class ArrayBuffer {
   char data() {
     visit([](auto buffer) -> char { // expected-note {{in instantiation}}
       buffer->data();
-    }); // expected-warning {{control reaches end of non-void lambda}}
-  } // expected-warning {{control reaches end of non-void function}}
+    }); // expected-warning {{non-void lambda does not return a value}}
+  } // expected-warning {{non-void function does not return a value}}
 };
 
 #else

clang/test/Sema/block-return-1.c

@@ -2,5 +2,5 @@
 
 int j;
 void foo() {
-  ^ (void) { if (j) return 1; }(); // expected-error {{control may reach end of non-void block}}
+  ^ (void) { if (j) return 1; }(); // expected-error {{non-void block does not return a value in all control paths}}
 }

clang/test/Sema/block-return-3.c

@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -fsyntax-only %s -verify -fblocks
 
 void foo() {
-  ^ int (void) { }(); // expected-error {{control reaches end of non-void block}}
+  ^ int (void) { }(); // expected-error {{non-void block does not return a value}}
 }

clang/test/Sema/freemain.c

@@ -6,4 +6,4 @@ void* allocate(long size);
 
 void* main(void* context, long size) {
   if (context) return allocate(size);
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}

clang/test/Sema/return.c

@@ -17,7 +17,7 @@ void test0() {
 }
 
 int test1() {
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test2() {
   a: goto a;
@@ -26,7 +26,7 @@ int test2() {
 int test3() {
   goto a;
   a: ;
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 
 void halt() {
@@ -54,11 +54,11 @@ int unknown_nohalt() {
 
 int test7() {
   unknown();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test8() {
   (void)(1 + unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int halt3() __attribute__((noreturn));
 
@@ -68,11 +68,11 @@ int test9() {
 
 int test10() {
   (void)(unknown() || halt3());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int test11() {
   (void)(unknown() && halt3());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int test12() {
   (void)(halt3() || unknown());
@@ -84,27 +84,27 @@ int test13() {
 
 int test14() {
   (void)(1 || unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test15() {
   (void)(0 || unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test16() {
   (void)(0 && unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test17() {
   (void)(1 && unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test18() {
   (void)(unknown_nohalt() && halt3());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int test19() {
   (void)(unknown_nohalt() && unknown());
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test20() {
   int i;
@@ -112,7 +112,7 @@ int test20() {
     return 0;
   else if (0)
     return 2;
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int test21() {
   int i;
@@ -125,7 +125,7 @@ int test21() {
 int test22() {
   int i;
   switch (i) default: ;
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int test23() {
   int i;
@@ -135,7 +135,7 @@ int test23() {
   case 2:
     return 2;
   }
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int test24() {
   int i;
@@ -155,7 +155,7 @@ int test25() {
 
 int test26() {
   0 ? halt3() : unknown();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int j;
 void (*fptr)() __attribute__((noreturn));
@@ -231,19 +231,19 @@ void test33() {
 
 // Test that 'static inline' functions are only analyzed for CFG-based warnings
 // when they are used.
-static inline int si_has_missing_return() {} // expected-warning{{control reaches end of non-void function}}
-static inline int si_has_missing_return_2() {}; // expected-warning{{control reaches end of non-void function}}
+static inline int si_has_missing_return() {} // expected-warning{{non-void function does not return a value}}
+static inline int si_has_missing_return_2() {}; // expected-warning{{non-void function does not return a value}}
 static inline int si_forward();
 static inline int si_has_missing_return_3(int x) {
   if (x)
    return si_has_missing_return_3(x+1);
-} // expected-warning{{control may reach end of non-void function}}
+} // expected-warning{{non-void function does not return a value in all control paths}}
 
 int test_static_inline(int x) {
   si_forward();
   return x ? si_has_missing_return_2() : si_has_missing_return_3(x);
 }
-static inline int si_forward() {} // expected-warning{{control reaches end of non-void function}}
+static inline int si_forward() {} // expected-warning{{non-void function does not return a value}}
 
 // Test warnings on ignored qualifiers on return types.
 const int ignored_c_quals(); // expected-warning{{'const' type qualifier on return type has no effect}}
@@ -319,7 +319,7 @@ int PR19074_positive(int x) {
   default:
     break;
   }
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 // sizeof(long) test.
 int sizeof_long() {
@@ -338,4 +338,4 @@ int return_statement_expression() {
     });
   else
     return 0;
-} // no-warning (used to be "control may reach end of non-void function")
+} // no-warning (used to be "non-void function does not return a value in all control paths")

clang/test/SemaCXX/attr-noreturn.cpp

@@ -10,7 +10,7 @@ namespace test5 {
 
   int &test1() {
     a.nofail();
-  } // expected-warning {{control reaches end of non-void function}}
+  } // expected-warning {{non-void function does not return a value}}
 
   int &test2() {
     a.fail();

clang/test/SemaCXX/coreturn.cpp

@@ -88,12 +88,12 @@ float test1() { co_await a; }
 
 int test2() {
   co_await a;
-} // expected-warning {{control reaches end of coroutine; which is undefined behavior because the promise type 'std::experimental::coroutine_traits<int>::promise_type' (aka 'promise_int') does not declare 'return_void()'}}
+} // expected-warning {{non-void coroutine does not return a value}}
 
 int test2a(bool b) {
   if (b)
     co_return 42;
-} // expected-warning {{control may reach end of coroutine; which is undefined behavior because the promise type 'std::experimental::coroutine_traits<int, bool>::promise_type' (aka 'promise_int') does not declare 'return_void()'}}
+} // expected-warning {{non-void coroutine does not return a value in all control paths}}
 
 int test3() {
   co_await a;
@@ -107,12 +107,12 @@ int test4() {
 
 void test5(int) {
   co_await a;
-} // expected-warning {{control reaches end of coroutine; which is undefined behavior because}}
+} // expected-warning {{non-void coroutine does not return a value}}
 
 void test6(int x) {
   if (x)
     co_return 42;
-} // expected-warning {{control may reach end of coroutine; which is undefined behavior because}}
+} // expected-warning {{non-void coroutine does not return a value in all control paths}}
 
 void test7(int y) {
   if (y)
@@ -132,9 +132,9 @@ VoidTagReturnVoid test9(bool b) {
 
 VoidTagReturnValue test10() {
   co_await a;
-} // expected-warning {{control reaches end of coroutine}}
+} // expected-warning {{non-void coroutine does not return a value}}
 
 VoidTagReturnValue test11(bool b) {
   if (b)
     co_return 42;
-} // expected-warning {{control may reach end of coroutine}}
+} // expected-warning {{non-void coroutine does not return a value in all control paths}}

clang/test/SemaCXX/return-noreturn.cpp

@@ -26,7 +26,7 @@ namespace abort_struct_complex_cfgs {
   }
   int f2_positive(int x) {
     switch (x) { default: ; }
-  } // expected-warning {{control reaches end of non-void function}}
+  } // expected-warning {{non-void function does not return a value}}
   int f3(int x) {
     switch (x) { default: { pr6884_abort_struct(); } }
   }
@@ -46,7 +46,7 @@ namespace abort_struct_complex_cfgs {
       pr6884_abort_struct *p = new pr6884_abort_struct();
       delete p;
     }
-  } // expected-warning {{control reaches end of non-void function}}
+  } // expected-warning {{non-void function does not return a value}}
 
   // Test that these constructs work even when extraneous blocks are created
   // before and after the switch due to implicit destructors.
@@ -61,7 +61,7 @@ namespace abort_struct_complex_cfgs {
   int g2_positive(int x) {
     other o;
     switch (x) { default: ; }
-  } // expected-warning {{control reaches end of non-void function}}
+  } // expected-warning {{non-void function does not return a value}}
   int g3(int x) {
     other o;
     switch (x) { default: { pr6884_abort_struct(); } }
@@ -140,7 +140,7 @@ template <PR9412_MatchType type> int PR9412_t() {
     default:
         break;
   }
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 void PR9412_f() {
     PR9412_t<PR9412_Exact>(); // expected-note {{in instantiation of function template specialization 'PR9412_t<PR9412_Exact>' requested here}}
@@ -165,7 +165,7 @@ int testTernaryStaticallyConditionalNoretrunOnTrue() {
 
 int testTernaryStaticallyConditionalRetrunOnTrue() {
   true ? Return() : NoReturn();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int testTernaryStaticallyConditionalNoretrunOnFalse() {
   false ? Return() : NoReturn();
@@ -173,23 +173,23 @@ int testTernaryStaticallyConditionalNoretrunOnFalse() {
 
 int testTernaryStaticallyConditionalRetrunOnFalse() {
   false ? NoReturn() : Return();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int testTernaryConditionalNoreturnTrueBranch(bool value) {
   value ? (NoReturn() || NoReturn()) : Return();
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testTernaryConditionalNoreturnFalseBranch(bool value) {
   value ? Return() : (NoReturn() || NoReturn());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testConditionallyExecutedComplexTernaryTrueBranch(bool value) {
   value || (true ? NoReturn() : true);
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testConditionallyExecutedComplexTernaryFalseBranch(bool value) {
   value || (false ? true : NoReturn());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testStaticallyExecutedLogicalOrBranch() {
   false || NoReturn();
@@ -201,19 +201,19 @@ int testStaticallyExecutedLogicalAndBranch() {
 
 int testStaticallySkippedLogicalOrBranch() {
   true || NoReturn();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int testStaticallySkppedLogicalAndBranch() {
   false && NoReturn();
-} // expected-warning {{control reaches end of non-void function}}
+} // expected-warning {{non-void function does not return a value}}
 
 int testConditionallyExecutedComplexLogicalBranch(bool value) {
   value || (true && NoReturn());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testConditionallyExecutedComplexLogicalBranch2(bool value) {
   (true && value) || (true && NoReturn());
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int testConditionallyExecutedComplexLogicalBranch3(bool value) {
   (false && (Return() || true)) || (true && NoReturn());
@@ -236,7 +236,7 @@ namespace LambdaVsTemporaryDtor {
   int bar() {
     X work([](){ Fatal(); });
     foo();
-  } // expected-warning {{control reaches end of non-void function}}
+  } // expected-warning {{non-void function does not return a value}}
 
   int baz() {
     FatalCopy fc;
@@ -250,12 +250,12 @@ namespace LambdaVsTemporaryDtor {
 int functionTryBlock1(int s) try {
   return 0;
 } catch (...) {
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int functionTryBlock2(int s) try {
 } catch (...) {
   return 0;
-} // expected-warning {{control may reach end of non-void function}}
+} // expected-warning {{non-void function does not return a value in all control paths}}
 
 int functionTryBlock3(int s) try {
   return 0;

clang/test/SemaCXX/warn-missing-noreturn.cpp

@@ -91,7 +91,7 @@ void rdar8875247_aux();
 
 int rdar8875247_test() {
   rdar8875247 f;
-} // expected-warning{{control reaches end of non-void function}}
+} // expected-warning{{non-void function does not return a value}}
 
 struct rdar8875247_B {
   rdar8875247_B();

clang/test/SemaTemplate/late-parsing-eager-instantiation.cpp

@@ -15,8 +15,8 @@ class ArrayBuffer {
   char data() {
     visit([](auto buffer) -> char { // expected-note {{in instantiation}}
       buffer->data();
-    }); // expected-warning {{control reaches end of non-void lambda}}
-  } // expected-warning {{control reaches end of non-void function}}
+    }); // expected-warning {{non-void lambda does not return a value}}
+  } // expected-warning {{non-void function does not return a value}}
 };
 
 // pr34185