[llvm-bugs] [Bug 28212] New: No diagnostic for declarations with incompatible enums

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28212

            Bug ID: 28212
           Summary: No diagnostic for declarations with incompatible enums
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ch3root at openwall.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

It seem the declaration (1) makes clang miss incompatibility of types between
the declarations (2) and (3). This is a constraints violation:

C11, 6.7p4: "All declarations in the same scope that refer to the same object
or function shall specify compatible types."

Source code:

----------------------------------------------------------------------
unsigned x; // (1)
enum { a } x; // (2)
enum { b } x; // (3)

int main()
{
}
----------------------------------------------------------------------

Results:

----------------------------------------------------------------------
$ clang -std=c11 -Weverything -O3 test.c && ./a.out
test.c:2:12: warning: no previous extern declaration for non-static variable
'x' [-Wmissing-variable-declarations]
enum { a } x;
           ^
1 warning generated.
----------------------------------------------------------------------

clang version: clang version 3.9.0 (trunk 271312)

For comparison:

----------------------------------------------------------------------
$ gcc -std=c11 -pedantic -Wall -Wextra -O3 test.c && ./a.out
test.c:3:12: error: conflicting types for ‘x’
 enum { b } x;
            ^
test.c:2:12: note: previous declaration of ‘x’ was here
 enum { a } x;
            ^
----------------------------------------------------------------------

gcc version: gcc (GCC) 7.0.0 20160616 (experimental)

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