[C23] Claim conformance to WG14 N3033

Clang has implemented __VA_OPT__ since Clang 12.

Author: AaronBallman

clang/test/C/C2x/n3033.c

@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -std=c23 -E %s | FileCheck %s
+
+/* WG14 N3033: Clang 12
+ * Comma ommission and deletion (__VA_OPT__)
+ */
+
+#define F(...)           f(0 __VA_OPT__(,) __VA_ARGS__)
+#define G(X, ...)        f(0, X __VA_OPT__(,) __VA_ARGS__)
+#define SDEF(sname, ...) S sname __VA_OPT__(= { __VA_ARGS__ })
+#define EMP
+
+F(a, b, c)        // replaced by f(0, a, b, c)
+// CHECK: f(0 , a, b, c)
+F()               // replaced by f(0)
+// CHECK: f(0 )
+F(EMP)            // replaced by f(0)
+// CHECK: f(0 )
+
+G(a, b, c)        // replaced by f(0, a, b, c)
+// CHECK: f(0, a , b, c)
+G(a, )            // replaced by f(0, a)
+// CHECK: f(0, a )
+G(a)              // replaced by f(0, a)
+// CHECK: f(0, a )
+
+SDEF(foo);        // replaced by S foo;
+// CHECK: S foo ;
+SDEF(bar, 1, 2);  // replaced by S bar = { 1, 2 };
+// CHECK: S bar = { 1, 2 };
+
+//#define H1(X, ...)       X __VA_OPT__(##) __VA_ARGS__  // error: ## may not appear at the beginning of a replacement list (6.10.3.3)
+
+#define H2(X, Y, ...)    __VA_OPT__(X ## Y,) __VA_ARGS__
+H2(a, b, c, d)    // replaced by ab, c, d
+// CHECK: ab, c, d
+
+#define H3(X, ...)       #__VA_OPT__(X##X X##X)
+H3(, 0)           // replaced by ""
+// CHECK: ""
+
+#define H4(X, ...)       __VA_OPT__(a X ## X) ## b
+H4(, 1)           // replaced by a b
+// CHECK: a b
+
+#define H5A(...)         __VA_OPT__()/**/__VA_OPT__()
+#define H5B(X)           a ## X ## b
+#define H5C(X)           H5B(X)
+H5C(H5A())        // replaced by ab
+// CHECK: ab
+

clang/test/C/C2x/n3033_2.c

@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c23 -verify %s
+
+#define H1(X, ...)       X __VA_OPT__(##) __VA_ARGS__ // expected-error {{'##' cannot appear at start of __VA_OPT__ argument}}
+

clang/www/c_status.html

@@ -1184,7 +1184,7 @@ <h2 id="c2x">C23 implementation status</h2>
     <tr>
       <td>Comma ommission and deletion (__VA_OPT__)</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3033.htm">N3033</a></td>
-      <td class="unknown" align="center">Unknown</td>
+      <td class="full" align="center">Clang 12</td>
     </tr>
     <tr>
       <td>Underspecified object definitions</td>