Non-POSIX-ism in command script interpretation

[Paul Smith]

The POSIX definition of make says this:

  When an escaped <newline> is found in a command line in a makefile,
  the command line shall contain the backslash, the <newline>, and the
  next line, except that the first character of the next line shall not
  be included if it is a <tab>.

GNU make does not handle this correctly if it uses the "fast path" and
invokes fork/exec directly, unless you put the \<nl> inside single
quotes.  It also doesn't handle the "slow path" properly, but I haven't
investigated that yet.

I believe that the above statement means that this makefile:

  all: fast1 fast2

  fast1: ; echo x\
  x

  fast2: ; echo x\
        x

should produce this:

  xx
  xx

But in fact it produces this:

  x x
  x x

This is because of this area of the code in
job.c:construct_command_argv_internal():

          case '\\':
            /* Backslash-newline combinations are eaten.  */
            if (p[1] == '\n')
              {
              swallow_escaped_newline:

                /* Eat the backslash, the newline, and following whitespace,
                   replacing it all with a single space.  */
    [...]

which then proceeds to do exactly as the comment says, except in the
case where we're inside a string--and the only time we find a \<nl>
inside a string in the fast path is inside single-quoted strings.


What do people think of modifying GNU make to confirm strictly to POSIX
here?  It seems like the right thing to do, but there _could_ be
backward-compatibility concerns, especially in the case of the second
example (test2) where the <tab> is removed; that means that makefiles
that currently say:

  foo: ; echo\
        hi

will now fail with an "unknown command: echohi" error.

I'll investigate the slow path situation next.

Anyone else have any comments on this?

-- 
-------------------------------------------------------------------------------
 Paul D. Smith <address@hidden> HASMAT: HA Software Mthds & Tools
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
-------------------------------------------------------------------------------
   These are my opinions---Nortel Networks takes no responsibility for them.