Add a "declared 'nonnull' here" note to warnings where an expression is checked against null.

[nlewycky]

Summary

Point to the relevant 'nonnull' or 'returns_nonnull' attribute when complaining about 'a == 0' or 'f() == 0' expressions.

[george.burgess.iv]

LGTM, thanks for the patch!

[nlewycky]

Closed by r272755.

include/clang/Basic/DiagnosticSemaKinds.td

 def err_enum_mode_vector_type : Error<
   "mode %0 is not supported for enumeration types">;
 def warn_attribute_nonnull_no_pointers : Warning<
   "'nonnull' attribute applied to function with no pointer arguments">,
   InGroup<IgnoredAttributes>;
 def warn_attribute_nonnull_parm_no_args : Warning<
   "'nonnull' attribute when used on parameters takes no arguments">,
   InGroup<IgnoredAttributes>;
+def note_declared_nonnull : Note<
+  "declared %select{'returns_nonnull'|'nonnull'}0 here">;
 def warn_attribute_sentinel_named_arguments : Warning<
   "'sentinel' attribute requires named arguments">,
   InGroup<IgnoredAttributes>;
 def warn_attribute_sentinel_not_variadic : Warning<
   "'sentinel' attribute only supported for variadic %select{functions|blocks}0">,
   InGroup<IgnoredAttributes>;
 def err_attribute_sentinel_less_than_zero : Error<
   "'sentinel' parameter 1 less than zero">;

lib/Sema/SemaChecking.cpp

unsigned DiagID = IsCompare
                           : diag::warn_address_of_reference_bool_conversion;
     PartialDiagnostic PD = PDiag(DiagID) << E->getSourceRange() << Range
                                          << IsEqual;
     if (CheckForReference(*this, E, PD)) {
       return;
     }
   }
 
-  auto ComplainAboutNonnullParamOrCall = [&](bool IsParam) {
+  auto ComplainAboutNonnullParamOrCall = [&](const Attr *NonnullAttr) {
+    bool IsParam = isa<NonNullAttr>(NonnullAttr);
     std::string Str;
     llvm::raw_string_ostream S(Str);
     E->printPretty(S, nullptr, getPrintingPolicy());
     unsigned DiagID = IsCompare ? diag::warn_nonnull_expr_compare
                                 : diag::warn_cast_nonnull_to_bool;
     Diag(E->getExprLoc(), DiagID) << IsParam << S.str()
       << E->getSourceRange() << Range << IsEqual;
+    Diag(NonnullAttr->getLocation(), diag::note_declared_nonnull) << IsParam;
   };
 
   // If we have a CallExpr that is tagged with returns_nonnull, we can complain.
   if (auto *Call = dyn_cast<CallExpr>(E->IgnoreParenImpCasts())) {
     if (auto *Callee = Call->getDirectCallee()) {
-      if (Callee->hasAttr<ReturnsNonNullAttr>()) {
-        ComplainAboutNonnullParamOrCall(false);
+      if (const Attr *A = Callee->getAttr<ReturnsNonNullAttr>()) {
+        ComplainAboutNonnullParamOrCall(A);
         return;
       }
     }
   }
 
   // Expect to find a single Decl.  Skip anything more complicated.
   ValueDecl *D = nullptr;
   if (DeclRefExpr *R = dyn_cast<DeclRefExpr>(E)) {
     D = R->getDecl();
   } else if (MemberExpr *M = dyn_cast<MemberExpr>(E)) {
     D = M->getMemberDecl();
   }
 
   // Weak Decls can be null.
   if (!D || D->isWeak())
     return;
 
   // Check for parameter decl with nonnull attribute
   if (const auto* PV = dyn_cast<ParmVarDecl>(D)) {
     if (getCurFunction() &&
         !getCurFunction()->ModifiedNonNullParams.count(PV)) {
-      if (PV->hasAttr<NonNullAttr>()) {
-        ComplainAboutNonnullParamOrCall(true);
+      if (const Attr *A = PV->getAttr<NonNullAttr>()) {
+        ComplainAboutNonnullParamOrCall(A);
         return;
       }
 
       if (const auto *FD = dyn_cast<FunctionDecl>(PV->getDeclContext())) {
         auto ParamIter = std::find(FD->param_begin(), FD->param_end(), PV);
         assert(ParamIter != FD->param_end());
         unsigned ParamNo = std::distance(FD->param_begin(), ParamIter);
 
         for (const auto *NonNull : FD->specific_attrs<NonNullAttr>()) {
           if (!NonNull->args_size()) {
-              ComplainAboutNonnullParamOrCall(true);
+              ComplainAboutNonnullParamOrCall(NonNull);
               return;
           }
 
           for (unsigned ArgNo : NonNull->args()) {
             if (ArgNo == ParamNo) {
-              ComplainAboutNonnullParamOrCall(true);
+              ComplainAboutNonnullParamOrCall(NonNull);
               return;
             }
           }
         }
       }
     }
   }
 

test/Sema/nonnull.c

 void redecl(void *, void *);
 void redecl_test(void *p) {
   redecl(p, 0); // expected-warning{{null passed}}
   redecl(0, p); // expected-warning{{null passed}}
 }
 
 // rdar://18712242
 #define NULL (void*)0
-__attribute__((__nonnull__))
+__attribute__((__nonnull__))  // expected-note 2{{declared 'nonnull' here}}
 int evil_nonnull_func(int* pointer, void * pv)
 {
    if (pointer == NULL) {  // expected-warning {{comparison of nonnull parameter 'pointer' equal to a null pointer is 'false' on first encounter}}
      return 0;
    } else {
      return *pointer;
    } 
 
    pointer = pv;
    if (!pointer)
      return 0;
    else
      return *pointer;
 
    if (pv == NULL) {} // expected-warning {{comparison of nonnull parameter 'pv' equal to a null pointer is 'false' on first encounter}}
 }
 
 void set_param_to_null(int**);
-int another_evil_nonnull_func(int* pointer, char ch, void * pv) __attribute__((nonnull(1, 3)));
+int another_evil_nonnull_func(int* pointer, char ch, void * pv) __attribute__((nonnull(1, 3)));  // expected-note 2{{declared 'nonnull' here}}
 int another_evil_nonnull_func(int* pointer, char ch, void * pv) {
    if (pointer == NULL) { // expected-warning {{comparison of nonnull parameter 'pointer' equal to a null pointer is 'false' on first encounter}}
      return 0;
    } else {
      return *pointer;
    } 
 
    set_param_to_null(&pointer);
    if (!pointer)
      return 0;
    else
      return *pointer;
 
    if (pv == NULL) {} // expected-warning {{comparison of nonnull parameter 'pv' equal to a null pointer is 'false' on first encounter}}
 }
 
 extern void *returns_null(void**);
 extern void FOO();
 extern void FEE();
 
 extern void *pv;
-__attribute__((__nonnull__))
+__attribute__((__nonnull__))  // expected-note {{declared 'nonnull' here}}
 void yet_another_evil_nonnull_func(int* pointer)
 {
  while (pv) {
    // This comparison will not be optimized away.
    if (pointer) {  // expected-warning {{nonnull parameter 'pointer' will evaluate to 'true' on first encounter}}
      FOO();
    } else {
      FEE();
    } 
    pointer = returns_null(&pv);
  }
 }
 
-void pr21668_1(__attribute__((nonnull)) const char *p, const char *s) {
+void pr21668_1(__attribute__((nonnull)) const char *p, const char *s) { // expected-note {{declared 'nonnull' here}}
   if (p) // expected-warning {{nonnull parameter 'p' will evaluate to 'true' on first encounter}}
     ;
   if (s) // No warning
     ;
 }
 
 void pr21668_2(__attribute__((nonnull)) const char *p) {
   p = 0;
   if (p) // No warning
     ;
 }
 
-__attribute__((returns_nonnull)) void *returns_nonnull_whee();
+__attribute__((returns_nonnull)) void *returns_nonnull_whee();  // expected-note 6{{declared 'returns_nonnull' here}}
 
 void returns_nonnull_warning_tests() {
   if (returns_nonnull_whee() == NULL) {} // expected-warning {{comparison of nonnull function call 'returns_nonnull_whee()' equal to a null pointer is 'false' on first encounter}}
 
   if (returns_nonnull_whee() != NULL) {} // expected-warning {{comparison of nonnull function call 'returns_nonnull_whee()' not equal to a null pointer is 'true' on first encounter}}
 
   if (returns_nonnull_whee()) {} // expected-warning {{nonnull function call 'returns_nonnull_whee()' will evaluate to 'true' on first encounter}}
   if (!returns_nonnull_whee()) {} // expected-warning {{nonnull function call 'returns_nonnull_whee()' will evaluate to 'true' on first encounter}}
 
   int and_again = !returns_nonnull_whee(); // expected-warning {{nonnull function call 'returns_nonnull_whee()' will evaluate to 'true' on first encounter}}
   and_again = !returns_nonnull_whee(); // expected-warning {{nonnull function call 'returns_nonnull_whee()' will evaluate to 'true' on first encounter}}
 }