trailing whitespace in make macros (was: bug#7868: splitting up test suites)

[Ralf Wildenhues]

[ moving from automake bug#7868 ]

* Ralf Wildenhues wrote on Sat, Jan 22, 2011 at 11:06:48AM CET:
> * Stefano Lattarini wrote on Thu, Jan 20, 2011 at 10:19:24PM CET:
> > On Thursday 20 January 2011, Ralf Wildenhues wrote:
> > > That is the reason the check-TESTS rule is so ugly (and recursive) in
> > > the first place.  I really would like to avoid more instances of this
> > > wart; so specifying files without extension is Not Good(TM).
> > >
> > OK, noted (and these considerations could IMHO end up somewhere in the
> > manual).
> 
> Good suggestion.  They should be mentioned in the portability section of
> autoconf.texi if they aren't already, and as ## comments in check.am.

Proposed patches for Automake maint and Autoconf below.

Thanks,
Ralf

    Add comment to check-TESTS rule working around make 3.80 bug.
    
    * lib/am/check.am (check-TESTS): Update comment.
    Suggestion by Stefano Lattarini.

diff --git a/lib/am/check.am b/lib/am/check.am
index 5728081..d792372 100644
--- a/lib/am/check.am
+++ b/lib/am/check.am
@@ -235,6 +235,9 @@ check-TESTS:
 ## OTOH, this means that, in the rule for `$(TEST_SUITE_LOG)', we
 ## cannot use `$?' to compute the set of lazily rerun tests, lest
 ## we rely on .PHONY to work portably.
+##
+## Work around a GNU make 3.80 bug expanding trailing whitespace in
+## `TESTS = foo.test $(empty)'  to `foo.log .log' in $(TESTS_LOGS).
        @test -z "$(TEST_SUITE_LOG)" || rm -f $(TEST_SUITE_LOG)
        @list='$(TEST_LOGS)';                                           \
        list=`for f in $$list; do                                       \




    docs: new sections about macros and comments, substitutions.
    
    * doc/autoconf.texi (Top, Portable Make): Adjust menus.
    (Comments in Make Macros, Trailing whitespace in Make Macros):
    New sections.
    Suggestion by Stefano Lattarini.

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index eee4ba7..0e8c3cc 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -533,6 +533,8 @@ Portable Make Programming
 * Parallel Make::               Parallel @command{make} quirks
 * Comments in Make Rules::      Other problems with Make comments
 * Newlines in Make Rules::      Using literal newlines in rules
+* Comments in Make Macros::     Other problems with Make comments in macros
+* Trailing whitespace in Make Macros::  Macro substitution problems
 * obj/ and Make::               Don't name a subdirectory @file{obj}
 * make -k Status::              Exit status of @samp{make -k}
 * VPATH and Make::              @code{VPATH} woes
@@ -19135,6 +19137,8 @@ itself.
 * Parallel Make::               Parallel @command{make} quirks
 * Comments in Make Rules::      Other problems with Make comments
 * Newlines in Make Rules::      Using literal newlines in rules
+* Comments in Make Macros::     Other problems with Make comments in macros
+* Trailing whitespace in Make Macros::  Macro substitution problems
 * obj/ and Make::               Don't name a subdirectory @file{obj}
 * make -k Status::              Exit status of @samp{make -k}
 * VPATH and Make::              @code{VPATH} woes
@@ -19575,6 +19579,55 @@ nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
 sed -e "s/\$$/address@hidden@}/" < input > output
 @end example
 
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
+syntax error at compile time:
+
address@hidden
+CPPFLAGS = "-DCOMMENT_CHAR='#'"
address@hidden example
+
address@hidden
+as @samp{CPPFLAGS} may be expanded to @samp{"-DCOMMENT_CHAR='#}.
+Luckily, most @command{make} implementations disregard this and treat
+single and double quotes specially here.
+
+Even without quoting involved, comments can have surprising effects,
+because the whitespace before them is part of the variable value:
+
address@hidden
+foo = bar # trailing comment
+print: ; @@echo "$(foo)."
address@hidden example
+
address@hidden
+prints @samp{bar .}, which is usually not intended, and can expose
address@hidden bugs as described below.
+
address@hidden Trailing whitespace in Make Macros
address@hidden Trailing whitespace in Make Macros
address@hidden whitespace in @file{Makefile} macros
address@hidden @file{Makefile} macros and whitespace
+
+GNU @command{make} 3.80 mistreats trailing whitespace in macro
+substitutions and appends another spurious suffix:
+
address@hidden
+empty =
+foo = bar $(empty)
+print: ; @@echo $(foo:=.test)
address@hidden example
+
address@hidden
+prints @samp{bar.test .test}.
+
 @node obj/ and Make
 @section The @file{obj/} Subdirectory and Make
 @cindex @file{obj/}, subdirectory