add additional diagnostics

Author: a-tarasyuk

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -7409,6 +7409,11 @@ def warn_c23_compat_utf8_string : Warning<
 def note_cxx20_c23_compat_utf8_string_remove_u8 : Note<
   "remove 'u8' prefix to avoid a change of behavior; "
   "Clang encodes unprefixed narrow string literals as UTF-8">;
+def warn_c23_compat_restrict_pointers_to_array : Warning<
+  "'restrict' qualifier on pointers to arrays is incompatible with C17 and earlier">,
+  InGroup<CPre23Compat>, DefaultIgnore;
+def ext_restrict_pointers_to_array_c23 : Extension<
+  "'restrict' qualifier on pointers to arrays is a C23 extension">, InGroup<C23>;
 def err_array_init_different_type : Error<
   "cannot initialize array %diff{of type $ with array of type $|"
   "with different type of array}0,1">;

clang/lib/Sema/SemaType.cpp

@@ -1616,9 +1616,15 @@ QualType Sema::BuildQualifiedType(QualType T, SourceLocation Loc,
       EltTy = T;
     }
 
+    Loc = DS ? DS->getRestrictSpecLoc() : Loc;
     if (DiagID) {
-      Diag(DS ? DS->getRestrictSpecLoc() : Loc, DiagID) << EltTy;
+      Diag(Loc, DiagID) << EltTy;
       Qs.removeRestrict();
+    } else {
+      if (!getLangOpts().C23 && (T->isArrayType() || EltTy->isArrayType())) {
+        Diag(Loc, diag::ext_restrict_pointers_to_array_c23);
+        Diag(Loc, diag::warn_c23_compat_restrict_pointers_to_array);
+      }
     }
   }
 

clang/test/Sema/pre-c2x-restrict-qualifier.c

@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -std=c23 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c17 -fsyntax-only -pedantic -verify=pedantic %s
+// RUN: %clang_cc1 -std=c17 -fsyntax-only -Wpre-c2x-compat -verify=pre-c2x-compat %s
+
+typedef int (*T1)[2];
+restrict T1 t1;         // pedantic-warning {{'restrict' qualifier on pointers to arrays is a C23 extension}} \
+                        // pre-c2x-compat-warning {{'restrict' qualifier on pointers to arrays is incompatible with C17 and earlier}}
+
+typedef int *T2[2];
+restrict T2 t2;         // pedantic-warning {{'restrict' qualifier on pointers to arrays is a C23 extension}} \
+                        // pre-c2x-compat-warning {{'restrict' qualifier on pointers to arrays is incompatible with C17 and earlier}}
+
+typedef int *T3[2][2];
+restrict T3 t3;         // pedantic-warning {{'restrict' qualifier on pointers to arrays is a C23 extension}} \
+                        // pre-c2x-compat-warning {{'restrict' qualifier on pointers to arrays is incompatible with C17 and earlier}}
+
+typedef int (*t4)();    // pedantic-warning {{a function declaration without a prototype is deprecated in all versions of C}}
+typedef t4 t5[2];
+typedef t5 restrict t6; // expected-error {{pointer to function type 'int (void)' may not be 'restrict' qualified}} \
+                        // pedantic-error {{pointer to function type 'int ()' may not be 'restrict' qualified}} \
+                        // pre-c2x-compat-error {{pointer to function type 'int ()' may not be 'restrict' qualified}}
+
+typedef int t7[2];
+typedef t7 restrict t8; // expected-error {{restrict requires a pointer or reference ('t7' (aka 'int[2]') is invalid)}} \
+                        // pedantic-error {{restrict requires a pointer or reference ('t7' (aka 'int[2]') is invalid)}} \
+                        // pre-c2x-compat-error {{restrict requires a pointer or reference ('t7' (aka 'int[2]') is invalid}}

clang/test/Sema/types.c

@@ -6,10 +6,10 @@
 // RUN: %clang_cc1 %s -fblocks -pedantic -verify -triple=powerpc64-ibm-aix-xcoff
 
 typedef int (*T)[2];
-restrict T x;
+restrict T x; // expected-warning {{'restrict' qualifier on pointers to arrays is a C23 extension}}
 
 typedef int *S[2];
-restrict S y;
+restrict S y; // expected-warning {{'restrict' qualifier on pointers to arrays is a C23 extension}}
 
 // int128_t is available.
 int a(void) {