RE: use of hyphen in recipes to ignore errors precludes using -- as comment character

[Kaz Kylheku (gmake)]

On 2021-02-21 22:52, Cook, Malcolm wrote:
> > On 2021-02-19 21:12, Cook, Malcolm wrote:
> > > Gnu manual reads:
> > >
> > > To ignore errors in a recipe line, write a '-' at the beginning of
> > > the line's text (after the initial tab)...
> > >
> > > I think it would be good if the implementation changed to allow 
> > > instead
> > >
> > > To ignore errors in a recipe line, write a '-' as the first character
> > > of the line's text (immediately after the initial tab with no other
> > > preceding whitespace)...
> >
> > I don't see the difference. There isn't any whitespace allowed between
> > the
> > tab and the minus.
>
> Why do you say this? According to what?

Simply, none of the documentation (POSIX, GNU Make manual) says
anything about any optional space before the - character, and
empirical testing shows no such whitespace is tolerated.

> > In any case, this is a POSIX feature:
> >
> > Makefile command lines can have one or more of the following
> > prefixes: a <hyphen-minus> ( '-' ), an at-sign ( '@' ), or a
> > <plus-sign> ( '+' ). These shall modify the way in which make
> > processes the command.
> >
> > - If the command prefix contains a <hyphen-minus>, or the -i
> > option is present, or the special target .IGNORE has either
> > the current target as a prerequisite or has no prerequisites,
> > any error found while executing the command shall be ignored.
> >
> > @ If the command prefix contains an at-sign and the make
> > utility command line -n option is not specified, or the -s
> > option is present, or the special target .SILENT has either
> > the current target as a prerequisite or has no prerequisites,
> > the command shall not be written to standard output before it
> > is executed.
> >
> > + If the command prefix contains a <plus-sign>, this
> > indicates a makefile command line that shall be executed even
> > if -n, -q, or -t is specified.
>
> I guess what is not clearly defined at least to me is what constitutes
> a "prefix".

I says "Makefile command lines can have one or more of these
prefixes: ...". Therefore, a prefix must be a mixture of those three
characters, and only those characters, immediately following
the tab.

> Apparently whitespace gets ignored in looking for a prefix.  To me
> this is unfortunate and what I am suggesting might be changed.

But it's not ignored; whitespace is simply not allowed in a prefix;
if whitespace is seen while scanning the prefix, the (possibly empty)
prefix has thereby ended. That space is the start of the line after
the prefix.

> > How are you embedding here strings into make recipes? That generally
> > doesn't work very well, unless perhaps you are using the GNU Make
> > extension which allows all of he lines of a recipe to be a single
> > shell script, rather than individual scripts.
>
> That is what I am doing, yes.
>
> .ONESHELL
>
> To me all this stuff about prefixes in the middle of a multiline
> recipe doesn't even make sense with .ONESHELL.

But there is no such thing, according to the documentation:

     If '.ONESHELL' is provided, then only the first line of the recipe
  will be checked for the special prefix characters ('@', '-', and '+').
  Subsequent lines will include the special characters in the recipe 
line
  when the 'SHELL' is invoked.  If you want your recipe to start with 
one
  of these special characters you'll need to arrange for them to not be
  the first characters on the first line, perhaps by adding a comment or
  similar.  For example, this would be a syntax error in Perl because 
the
  first '@' is removed by make:

     .ONESHELL:
     SHELL = /usr/bin/perl
     .SHELLFLAGS = -e
     show :
             @f = qw(a b c);
             print "@f\n";

Cheers ...