llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Constantin Kronbichler (ccrownhill)
<details>
<summary>Changes</summary>
This fixes issue #<!-- -->39558 which mentions the problem when compiling the
following code with `-pedantic-errors` flag (it also mentions `-Wall -Wextra`
but those shouldn't change the output, which is also the case in GCC):
```c
static void f();
int main()
{
f;
}
```
Clang only outputs an `undefined-internal` warning on the first line, but
according to 6.9/3
```
"... Moreover, if an identifier declared with internal linkage is used in an
expression (other than as a part of the operand of a sizeof or _Alignof
operator whose result is an integer constant), there shall be exactly one
external definition for the identifier in the translation unit."
```
this should be illegal and hence an error.
I fixed this by changing the warning type from `Warning` to `ExtWarn` and by
adding a suitable test.
---
Full diff: https://github.com/llvm/llvm-project/pull/98016.diff
2 Files Affected:
- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+1-1)
- (added) clang/test/Sema/undefined_internal.c (+11)
``````````diff
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 44fd51ec9abc9..ae3dbedd01693 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6013,7 +6013,7 @@ def note_deleted_assign_field : Note<
"because field %2 is of %select{reference|const-qualified}4 type %3">;
// These should be errors.
-def warn_undefined_internal : Warning<
+def warn_undefined_internal : ExtWarn<
"%select{function|variable}0 %q1 has internal linkage but is not defined">,
InGroup<DiagGroup<"undefined-internal">>;
def err_undefined_internal_type : Error<
diff --git a/clang/test/Sema/undefined_internal.c
b/clang/test/Sema/undefined_internal.c
new file mode 100644
index 0000000000000..1b6c3a4b76e05
--- /dev/null
+++ b/clang/test/Sema/undefined_internal.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -pedantic-errors
+
+static void f(void); // expected-error {{function 'f' has internal linkage but
is not defined}}
+
+int main(void)
+{
+ f;
+ // expected-note@-1 {{used here}}
+ // expected-warning@-2 {{expression result unused}}
+}
+
``````````
</details>
https://github.com/llvm/llvm-project/pull/98016
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