[LLVMbugs] [Bug 20634] New: clang incorrectly parses array declarators in sizeof operand.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20634

            Bug ID: 20634
           Summary: clang incorrectly parses array declarators in sizeof
                    operand.
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: nbowler at draconx.ca
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Consider the following C program:

  #include <stdio.h>

  int main(void)
  {
    printf("%zu\n", sizeof (struct { int a; } [2]));
    return 0;
  }

While unusual, there is no problem with this type name from the C
grammar productions (from n1570, but I don't believe these are
changed significantly from earlier revisions):

  type-name
    -> specifier-qualifier-list abstract-declarator
    -> type-specifier abstract-declarator
    -> struct-or-union-specifier abstract-declarator
    -> struct-or-union { struct-declaration-list } abstract-declarator
    -> struct { struct-declaration-list } abstract-declarator
    -> struct { struct-declaration-list } direct-abstract-declarator
    -> struct { struct-declaration-list } [ assignment-expression ]

and so on.

The problem appears to be specific to array abstract declarators used in
this manner, sizeof expressions with more ridiculous type names such as:

  sizeof (struct { int a; } (*[2])(struct { int a; }))

appear to work just fine in clang.  With clang, the program is rejected
with this pile of error messages:

  % clang -O -std=c11 -Wall -pedantic test.c  
  test.c:5:46: error: expected ';' after struct
      printf("%zu\n", sizeof (struct { int a; } [2]));
                                               ^
                                               ;
  test.c:5:47: error: expected ')'
      printf("%zu\n", sizeof (struct { int a; } [2]));
                                                ^
  test.c:5:28: note: to match this '('
      printf("%zu\n", sizeof (struct { int a; } [2]));
                             ^
  test.c:5:47: error: expected ')'
      printf("%zu\n", sizeof (struct { int a; } [2]));
                                                ^
  test.c:5:11: note: to match this '('
      printf("%zu\n", sizeof (struct { int a; } [2]));
            ^
  test.c:5:47: error: expected expression
      printf("%zu\n", sizeof (struct { int a; } [2]));
                                                ^
  4 errors generated.

None of the error messages are helpful.  GCC accepts the program and
works correctly.

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