[whitespace/parens] Spurious warning within comment

[alejandro-colomar]

cpplint(1) is triggering a warning from something that resembles a function but within a comment. Comments can have anything in them, and doesn't necessarily represent a function (and in this case, obviously isn't).

alx@asus5775:~/src/linux/man-pages/man-pages$ cat tmp/src/man3/dlopen.3.d/dlopen.c

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

#include <gnu/lib-names.h>  /* Defines LIBM_SO (which will be a
                               string such as "libm.so.6") */
int
main(void)
{
    void *handle;
    double (*cosine)(double);
    char *error;

    handle = dlopen(LIBM_SO, RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    dlerror();    /* Clear any existing error */

    cosine = (double (*)(double)) dlsym(handle, "cos");

    /* According to the ISO C standard, casting between function
       pointers and 'void *', as done above, produces undefined results.
       POSIX.1-2001 and POSIX.1-2008 accepted this state of affairs and
       proposed the following workaround:

           *(void **) (&cosine) = dlsym(handle, "cos");

       This (clumsy) cast conforms with the ISO C standard and will
       avoid any compiler warnings.

       The 2013 Technical Corrigendum 1 to POSIX.1-2008 improved matters
       by requiring that conforming implementations support casting
       'void *' to a function pointer.  Nevertheless, some compilers
       (e.g., gcc with the '-pedantic' option) may complain about the
       cast used in this program. */

    error = dlerror();
    if (error != NULL) {
        fprintf(stderr, "%s\n", error);
        exit(EXIT_FAILURE);
    }

    printf("%f\n", (*cosine)(2.0));
    dlclose(handle);
    exit(EXIT_SUCCESS);
}

alx@asus5775:~/src/linux/man-pages/man-pages$ make tmp/src/man3/dlopen.3.d/dlopen.lint-c.cpplint.touch V=1
LINT (cpplint)	tmp/src/man3/dlopen.3.d/dlopen.lint-c.cpplint.touch
cpplint   tmp/src/man3/dlopen.3.d/dlopen.c >/dev/null
tmp/src/man3/dlopen.3.d/dlopen.c:6:  Extra space before ( in function call  [whitespace/parens] [4]
make: *** [lib/lint-c.mk:64: tmp/src/man3/dlopen.3.d/dlopen.lint-c.cpplint.touch] Error 1

[tkruse]

Thanks for reporting.
cpplint is not great at dealing with multiline /* ... */ comments. cpplint is not based on a parser, but on rules checking line by line. As such, handling complex multiline comments can cause it to report false positives. I don't think this will be fixed in the future.

[alejandro-colomar]

I modified the above program to actually use the line that was in the comment, to see what would happen:

$ cat tmp/src/man3/dlopen.3.d/dlopen.c

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

#include <gnu/lib-names.h>  /* Defines LIBM_SO (which will be a
                               string such as "libm.so.6") */
int
main(void)
{
    void *handle;
    double (*cosine)(double);
    char *error;

    handle = dlopen(LIBM_SO, RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(EXIT_FAILURE);
    }

    dlerror();    /* Clear any existing error */

//    cosine = (double (*)(double)) dlsym(handle, "cos");

    *(void **) (&cosine) = dlsym(handle, "cos");

    error = dlerror();
    if (error != NULL) {
        fprintf(stderr, "%s\n", error);
        exit(EXIT_FAILURE);
    }

    printf("%f\n", (*cosine)(2.0));
    dlclose(handle);
    exit(EXIT_SUCCESS);
}

That line of code is fine, according to the standards. But cpplint(1) still warns; see below.

$ make V=1 lint-c-cpplint
LINT (cpplint)	tmp/src/man3/dlopen.3.d/dlopen.lint-c.cpplint.touch
cpplint   tmp/src/man3/dlopen.3.d/dlopen.c >/dev/null
tmp/src/man3/dlopen.3.d/dlopen.c:6:  Extra space before ( in function call  [whitespace/parens] [4]
tmp/src/man3/dlopen.3.d/dlopen.c:25:  Weird number of spaces at line-start.  Are you using a 2-space indent?  [whitespace/indent] [3]
make: *** [lib/lint-c.mk:64: tmp/src/man3/dlopen.3.d/dlopen.lint-c.cpplint.touch] Error 1

However, it makes sense if cpplint(1) is not powerful enough to parse such complex lines of code, and would understand if it can't be fixed without important changes to the program.

[tkruse]

I believe the warning is about this comment:

#include <gnu/lib-names.h>  /* Defines LIBM_SO (which will be a
                               string such as "libm.so.6") */

And I think cpplint has trouble identiifying /* when it's not at the start of a line, because it could be something like ("bla /*...").

[alejandro-colomar]

Ahh, yes, sorry, I forgot about it :)