| Issue |
178863
|
| Summary |
clang accepts conflicting static/extern variable declarations in same translation unit without diagnostic
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
vrukesh
|
**What code / commands /steps will reproduce the problem?**
Compile below sample code for C++17.
Godbolt compile explorer: https://godbolt.org/z/5YKqshsdf
`
static int k = 3;
extern int foo(int);
int main() {
return foo(k);
}
extern int k;
int foo(int p) {
return p == k;
}
`
**What is the expected result?**
Per C++17 this must be a compile-time error (not just a warning)
**What happens instead?**
Compilation is successful, without any warning/error.
As per the standard:
A type without linkage shall not be used as the type of a variable or function with external linkage unless
-the entity has C language linkage, or
- the entity is declared within an unnamed namespace, or
- the entity is not odr-used or is defined in the same translation unit.
Translation unit declares `k` with internal linkage (`static int k = 3;`) and then redeclares the same name with external linkage (`extern int k;`). That mix of linkage is ill-formed in C++17. If an entity is declared with internal linkage, then any redeclaration in the same translation unit must also give it internal linkage; giving it external linkage instead makes the program ill‑formed. The above `static` then `extern` redeclarations violate that rule.
Accepting the code without diagnostic is non‑conforming.
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