[clang] 456fa47 - [C2y] Claim conformance to WG14 N3505

[Aaron Ballman via cfe-commits]

Author: Aaron Ballman
Date: 2025-03-11T15:04:11-04:00
New Revision: 456fa47bab479f0ef1136d07687bd1b2635b1a26

URL: https://github.com/llvm/llvm-project/commit/456fa47bab479f0ef1136d07687bd1b2635b1a26
DIFF: https://github.com/llvm/llvm-project/commit/456fa47bab479f0ef1136d07687bd1b2635b1a26.diff

LOG: [C2y] Claim conformance to WG14 N3505

This paper clarified that conditional inclusion in the preprocessor
requires the integer constant expression to be comprised only of
integer and character literals, punctuators, or implementation-defined
tokens.

This is something Clang has always required.

Added: 
    clang/test/C/C2y/n3505.c

Modified: 
    clang/www/c_status.html

Removed: 
    


################################################################################
diff  --git a/clang/test/C/C2y/n3505.c b/clang/test/C/C2y/n3505.c
new file mode 100644
index 0000000000000..7f307390e09ca
--- /dev/null
+++ b/clang/test/C/C2y/n3505.c
@@ -0,0 +1,32 @@
+// RUN: %clang_cc1 -verify -std=c2y -Wall -pedantic %s
+// RUN: %clang_cc1 -verify -std=c23 -Wall -pedantic %s
+// RUN: %clang_cc1 -verify -std=c11 -Wall -pedantic %s
+// RUN: %clang_cc1 -verify -std=c99 -Wall -pedantic %s
+
+/* WG14 N3505: Yes
+ * Preprocessor integer expressions, v. 2
+ *
+ * This introduces a constraint that preprocessing tokens must be an integer
+ * literal, character literal, punctuator, or some other implementation-defined
+ * sequence of tokens (to support builtins that insert odd tokens into the
+ * parsing stream).
+ */
+
+// This is technically an integer constant expression, but it does not match
+// the new constraints and thus needs to be diagnosed.
+#if 1 ? 1 : (""[0] += 5) // expected-error {{invalid token at start of a preprocessor expression}}
+#endif
+
+// But with a character literal, it is fine.
+#if 1 ? 1 : ('a' + 5) // Ok
+#endif
+
+// This doesn't mean that all punctuators are fine, however.
+#if 1 ? 1 : ('a' += 5) // expected-error {{token is not a valid binary operator in a preprocessor subexpression}}
+#endif
+
+// But some are.
+#if 1 ? 1 : ~('a') // Ok
+#endif
+
+int x; // Needs a declaration to avoid a pedantic warning

diff  --git a/clang/www/c_status.html b/clang/www/c_status.html
index af3415e663e9d..4432e62b47520 100644
--- a/clang/www/c_status.html
+++ b/clang/www/c_status.html
@@ -268,7 +268,7 @@ <h2 id="c2y">C2y implementation status</h2>
     <tr>
       <td>Preprocessor integer expressions, v. 2</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3505.pdf">N3505</a></td>
-      <td class="unknown" align="center">Unknown</td>
+      <td class="full" align="center">Yes</td>
 	</tr>
     <tr>
       <td>Initialization of anonymous structures and unions</td>