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Re: trailing whitespace in make macros

From: Eric Blake
Subject: Re: trailing whitespace in make macros
Date: Sat, 22 Jan 2011 07:03:02 -0700
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[dropping automake-patches]

On 01/22/2011 03:19 AM, Ralf Wildenhues wrote:
>> Good suggestion.  They should be mentioned in the portability section of
>> autoconf.texi if they aren't already, and as ## comments in
> Proposed patches for Automake maint and Autoconf below.

In addition to Stefano's review...

> address@hidden Comments in Make Macros
> address@hidden Comments in Make Macros
> address@hidden Comments in @file{Makefile} macros
> address@hidden @file{Makefile} macros and comments
> +
> +Avoid putting comments in macro values as far as possible.  Posix
> +specifies that the text starting from the @samp{#} sign until the end of
> +the line is to be ignored, which has the unfortunate effect of
> +disallowing them even quoted.  Thus, the following might lead to a

s/even quoted/even within quotes/

> address@hidden
> +prints @samp{bar .}, which is usually not intended, and can expose
> address@hidden bugs as described below.

Should we also mention the converse issue of non-comments?  That is,
Posix requires that # embedded in the middle of a rule (and not a macro)
is okay.  Which is why gnulib's include-next module works - it
AC_SUBST's PRAGMA_COLUMNS as "#pragma COLUMNS 80" on some platforms, but
as long as it uses constructs like:

arpa/inet.h: ...
        sed -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
            -e 's|@''HAVE_FEATURES_H''@|$(HAVE_FEATURES_H)|g' \

then the resulting literal # in @PRAGMA_COLUMNS@ (and not
$(PRAGMA_COLUMNS)) works as intended.  That is, gnulib prefers using
$(var), but must use @var@ if var contains a literal #.

But that's enough additional detail that you can propose it as a
followup patch, without holding this one up.  So ACK to this one with
the nits fixed.

Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library

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