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@llvm/pr-subscribers-clang

Author: NohHyeon Kwon (swote-git)

diff --git a/clang/test/Preprocessor/cxx_oper_comma.cpp b/clang/test/Preprocessor/cxx_oper_comma.cpp
new file mode 100644
index 0000000000000..5589024ede01c
--- /dev/null
+++ b/clang/test/Preprocessor/cxx_oper_comma.cpp
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++98
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++11
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++14
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++17
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++20
+// RUN: %clang_cc1 -E -pedantic-errors %s -verify -std=c++23
+
+// Test 1: Top-level comma
+// expected-error@+1 {{expected end of line in preprocessor expression}}
+#if 1, 2
+#endif
+
+// Test 2: Comma in conditional expression
+// expected-error@+1 {{comma operator in operand of #if}}
+#if 1 ? 1, 0 : 3
+#endif
+
+// Test 3: Parenthesized comma
+// expected-error@+1 {{comma operator in operand of #if}}
+#if (1, 2)
+#endif
+
+// Test 4: Multiple commas
+// expected-error@+1 {{expected end of line in preprocessor expression}}
+#if 1, 2, 3
+#endif

Currently, this only about adding test code.

While adding these tests, I noticed two potential improvements to the current error message "comma operator in operand of #if":

1. The same message appears for #elif, #ifdef, etc.
2. Per CWG 1436, comma operators are explicitly not permitted in preprocessor conditionals. The current message describes where the comma is, but doesn't clearly convey why it's prohibited.

A clearer message should be more clear.

@Sirraide Thanks for your review!

Should I move this to clang/test/CXX/drs/cwg1436.cpp and format it according to the DR test conventions?

Should I move this to clang/test/CXX/drs/cwg1436.cpp and format it according to the DR test conventions?

Something like that yeah; I think there might already be a file that contains some of the 14XX tests somewhere but I’m not sure; I’ve tagged Vlad about this who should be able to tell you where exactly to put it.

@shafik was https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#3017 resolved ?

Should I move this to clang/test/CXX/drs/cwg1436.cpp and format it according to the DR test conventions?

Something like that yeah; I think there might already be a file that contains some of the 14XX tests somewhere but I’m not sure; I’ve tagged Vlad about this who should be able to tell you where exactly to put it.

Yes, please!

There are some tests in clang/test/Preprocessor/expr_invalid_tok.c right now. Found with a regex find in files #if\s+.*,.

@DavidSpickett Thanks for your help.

I can see similar test in expr_invalid_tok.c

// PR2284 - The constant-expr production does not including comma.
// CHECK: [[@LINE+1]]:14: error: expected end of line in preprocessor expression
#if 1 ? 2 : 0, 1
#endif

What I wanted to write a little more comprehensively was because of the contents of expr_comma.c.

// Comma is not allowed in C89
// RUN: not %clang_cc1 -E %s -std=c89 -pedantic-errors

// Comma is allowed if unevaluated in C99
// RUN: %clang_cc1 -E %s -std=c99 -pedantic-errors 

// PR2279

#if 0? 1,2:3
#endif

I'd love if this PR added tests for Core issues 1436 and 3017, but I don't see which wording we should test against. The only proposed resolution from 2012-02 by Richard is obviously incomplete.

I think we shouldn't touch DR tests until more information from Core arrives.

@Endilll Thanks for pointing out CWG 3017.
"Test 2" is testing exactly the same case as the CWG 3017 example:

// Test 2: Comma in conditional expression
// expected-error@+1 {{comma operator in operand of #if}}
#if 1 ? 1, 0 : 3
#endif

Should I add a comment referencing CWG 3017 to make this connection explicit?

Sure, additional context never hurts.

@DavidSpickett @Endilll i made changes for adding context(cwg3017) and adding tests(#elif , #if ,).

Please review when you have time.

Tests look fine to me now, but deferring to @Endilll as the domain expert here.

@shafik was https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#3017 resolved ?

No, it is still active. It looks like CWG1436 is where the action will be moving forward.

I think this is good to go after you add #if , test suggested earlier

Regarding the #if , test case, I believe I've already added it in the previous version of the patch(test 6). You can find it right here on line36-39.

Thanks for your support!

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