[clang] [Clang] allow restrict qualifier for array types with pointer types as element types (PR #120896)

[Aaron Ballman via cfe-commits]

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+// RUN: %clang_cc1 -std=c23 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c17 -fsyntax-only -pedantic -verify=pedantic %s
+// RUN: %clang_cc1 -std=c2x -fsyntax-only -Wpre-c2x-compat -verify=c2x-compat %s
+
+typedef int (*T1)[2];
+restrict T1 t1;
+
+typedef int *T2[2];
+restrict T2 t2;         // pedantic-warning {{'restrict' qualifier on an array of pointers is a C23 extension}} \
+                        // c2x-compat-warning {{'restrict' qualifier on an array of pointers is incompatible with C standards before C23}}
+
+typedef int *T3[2][2];
+restrict T3 t3;         // pedantic-warning {{'restrict' qualifier on an array of pointers is a C23 extension}} \
+                        // c2x-compat-warning {{'restrict' qualifier on an array of pointers is incompatible with C standards before C23}}
+
+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}} \
+                        // c2x-compat-error {{pointer to function type 'int (void)' 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)}} \
+                        // c2x-compat-error {{restrict requires a pointer or reference ('t7' (aka 'int[2]') is invalid}}
----------------
AaronBallman wrote:

```suggestion
typedef t7 restrict t8; // expected-error {{restrict requires a pointer or reference ('t7' (aka 'int[2]') is invalid)}}
```

https://github.com/llvm/llvm-project/pull/120896