[Bug preprocessor/63670] New: Ending C_INCLUDE_PATH with a trailing colon broken

[nightstrike at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63670

            Bug ID: 63670
           Summary: Ending C_INCLUDE_PATH with a trailing colon broken
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nightstrike at gmail dot com

If the C_INCLUDE_PATH environment variable ends with a colon, which can happen
with typical "prepend" scripts of the form:

C_INCLUDE_PATH=/path:$C_INCLUDE_PATH

then gcc will treat every file included with <> instead of "" as being a system
header, and will not generate any warnings.  The following is a test case that
I have been using, as I got burned on a bug from not seeing the warning that
set me back several days:

a.c:
int f() {}

b.c:
#include <a.c>



Expected output:
$ gcc b.c -Wall
./a.c: In function ‘f’:
./a.c:1:1: warning: control reaches end of non-void function [-Wreturn-type]
 int f() {}
 ^


However:
$ export C_INCLUDE_PATH=:
$ gcc b.c -Wall


** No output **