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.IGNORE: target doesn't work (with fix)

From: Mark Eichin
Subject: .IGNORE: target doesn't work (with fix)
Date: Thu, 15 Sep 2005 18:58:06 -0400 (EDT)

I was trying to determine why this Makefile:

                exit 1
        .IGNORE: thing
        all: thing

still fails, even with a fresh source build:

      $ ./make -f /tmp/Makefile all
      exit 1
      make: *** [thing] Error 1

A bit of code diving turned up this obvious-looking bit of job.c, in

  p = child->command_ptr;
  child->noerror = flags & COMMANDS_NOERROR;

Bracketing it with printfs told me that while (flags &
COMMANDS_NOERROR) was non-zero, child->noerror was zero on both sides.
But then I remembered that this is C, and not a high level

        (gdb) ptype child
        type = struct child {
            struct child *next;
            struct file *file;
            char **environment;
            char **command_lines;
            unsigned int command_line;
            char *command_ptr;
            pid_t pid;
            char *sh_batch_file;
            unsigned int remote : 1;
            unsigned int noerror : 1;
            unsigned int good_stdin : 1;
            unsigned int deleted : 1;
        } *

        (gdb) p child->noerror = 4
        warning: Value does not fit in 1 bits.
        $3 = 0
        (gdb) p child->noerror = 1
        $4 = 1

There doesn't appear to be a gcc warning to cover this case (possibly
because any warning would explode on *all* arithmetic expressions
involving bitfields... though that might actually be beneficial :-)

The "obvious" if a bit ugly fix:
  child->noerror = !!(flags & COMMANDS_NOERROR);

Works as expected, if you can stomach interpreting !! as a "cast to
boolean" idiom (this is the version I actually tested.)

  child->noerror = (flags & COMMANDS_NOERROR)? 1 : 0;

might be clearer.

I've appended a "tests/scripts/features/ignore" script which is
basically a quick edit of tests/scripts/features/comments - it's not
quite right, but it's a starting point and might help figure out if
this feature ever worked :-)  [As it is derived from the existing one,
I'm hoping you can just take it.]

                        _Mark_ <address@hidden>

# start of ignore script

$description = "The following test creates a makefile to test .IGNORE\n";

$details = "Set up a rule that does an exit 1, then .IGNORE it.\n";

open(MAKEFILE,"> $makefile");

# The Contents of the MAKEFILE ...

print MAKEFILE <<\EOF;
        exit 1
        @echo There should be no errors for this makefile.

.IGNORE: thing

all: thing

# END of Contents of MAKEFILE



# Create the answer to what should be produced by this Makefile
$answer = "There should be no errors for this makefile.\n";



# end of script

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