[clang] [clang][C23] Claim N3030 Enhancements to Enumerations supported (PR #107260)

[Mariya Podchishchaeva via cfe-commits]

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+// RUN: %clang_cc1 -verify -triple x86_64-unknown-linux-gnu -fsyntax-only --embed-dir=%S/Inputs -std=c23 %s -pedantic -Wall
+
+#include <limits.h>
+
+enum us : unsigned short {
+  us_max = USHRT_MAX,
+  us_violation,  // expected-error {{enumerator value 65536 is not representable in the underlying type 'unsigned short'}}
+                 // expected-warning at -1 {{overflow}}
+  us_violation_2 = us_max + 1, // expected-error {{enumerator value is not representable in the underlying type 'unsigned short'}}
+  us_wrap_around_to_zero = (unsigned short)(USHRT_MAX + 1) /* Okay: conversion
+                            done in constant expression before conversion to
+                            underlying type: unsigned semantics okay. */
+};
+
+enum ui : unsigned int {
+  ui_max = UINT_MAX,
+  ui_violation,  // expected-error {{enumerator value 4294967296 is not representable in the underlying type 'unsigned int'}}
+                 // expected-warning at -1 {{overflow}}
+  ui_no_violation = ui_max + 1,
+  ui_wrap_around_to_zero = (unsigned int)(UINT_MAX + 1)
+};
+
+enum E1 : short;
+enum E2 : short; // expected-note {{previous}}
+enum E3; // expected-warning {{ISO C forbids forward references to 'enum' types}}
+enum E4 : unsigned long long;
+
+enum E1 : short { m11, m12 };
+enum E1 x = m11;
+
+enum E2 : long { // expected-error {{enumeration redeclared with different underlying type 'long' (was 'short')}}
+  m21,
+  m22
+};
+
+enum E3 { // expected-note {{definition of 'enum E3' is not complete until the closing '}'}}
+          // expected-note at -1 {{previous}}
+  m31,
+  m32,
+  m33 = sizeof(enum E3) // expected-error {{invalid application of 'sizeof' to an incomplete type 'enum E3'}}
+};
+enum E3 : int; // expected-error {{enumeration previously declared with nonfixed underlying type}}
+
+enum E4 : unsigned long long {
+  m40 = sizeof(enum E4),
+  m41 = ULLONG_MAX,
+  m42 // expected-error {{enumerator value 18446744073709551616 is not representable in the underlying type 'unsigned long long'}}
+};
+
+enum E5 y; // expected-error {{tentative definition has type 'enum E5' that is never completed}}
+           // expected-warning at -1 {{ISO C forbids forward references to 'enum' types}}
+           // expected-note at -2 {{forward declaration of 'enum E5'}}
+enum E6 : long int z;   // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+enum E7 : long int = 0;  // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+                         // expected-error at -1 {{expected identifier or '('}}
+
+enum underlying : unsigned char { b0 };
+
+constexpr int a = _Generic(b0, int: 2, unsigned char: 1, default: 0);
+constexpr int b = _Generic((enum underlying)b0, int: 2, unsigned char: 1, default: 0);
+static_assert(a == 1);
+static_assert(b == 1);
+
+void f1(enum a : long b); // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+                          // expected-warning at -1 {{declaration of 'enum a' will not be visible outside of this function}}
+void f2(enum c : long{x} d); // expected-warning {{declaration of 'enum c' will not be visible outside of this function}}
+enum e : int f3(); // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+
+typedef enum t u; // expected-warning {{ISO C forbids forward references to 'enum' types}}
+typedef enum v : short W; // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+typedef enum q : short { s } R;
+
+struct s1 {
+  int x;
+  enum e:int : 1; // expected-error {{non-defining declaration of enumeration with a fixed underlying type is only permitted as a standalone declaration; missing list of enumerators?}}
+  int y;
+};
+
+enum forward; // expected-warning {{ISO C forbids forward references to 'enum' types}}
+extern enum forward fwd_val0;  /* Constraint violation: incomplete type */
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Fznamznon wrote:

This example is taken directly from the paper. gcc gives the same set of diagnostics here. The paper says there should be errors, however the area is covered with lots of extensions, so I'm not sure if I'm missing some historical context here.
Please let me know what you think.

https://github.com/llvm/llvm-project/pull/107260