From: Paul Eggert <eggert@cs.ucla.edu>
Date: Sat, 1 Jun 2024 16:07:38 +0000 (-0700)
Subject: Document Solaris ‘make’ glitch with ‘!’
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e51e789ac9953ad75574784cf3cb5d04c703805b;p=thirdparty%2Fautoconf.git

Document Solaris ‘make’ glitch with ‘!’

* doc/autoconf.texi (Failure in Make Rules):
Document that there are some complicated exceptions to
the idea that sh -e exits if any subcommand fails.
(Command Line Prefixes): New section.
---

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index c36eefdbe..9c05eceea 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -527,7 +527,8 @@ Portable Make Programming
 
 * $< in Ordinary Make Rules::   $< in ordinary rules
 * Failure in Make Rules::       Failing portably in rules
-* Special Chars in Names::      Special Characters in Macro Names
+* Command Line Prefixes::       What's at the start of makefile command lines
+* Special Chars in Names::      Special characters in macro names
 * Backslash-Newline-Empty::     Empty lines after backslash-newline
 * Backslash-Newline Comments::  Spanning comments across line boundaries
 * Long Lines in Makefiles::     Line length limitations
@@ -20379,7 +20380,8 @@ itself.
 @menu
 * $< in Ordinary Make Rules::   $< in ordinary rules
 * Failure in Make Rules::       Failing portably in rules
-* Special Chars in Names::      Special Characters in Macro Names
+* Command Line Prefixes::       What's at the start of makefile command lines
+* Special Chars in Names::      Special characters in macro names
 * Backslash-Newline-Empty::     Empty lines after backslash-newline
 * Backslash-Newline Comments::  Spanning comments across line boundaries
 * Long Lines in Makefiles::     Line length limitations
@@ -20411,10 +20413,13 @@ later) @command{make} diagnoses these uses and errors out.
 @node Failure in Make Rules
 @section Failure in Make Rules
 
+Unless errors are being ignored
+(e.g., because a makefile command line is preceded by a @samp{-} prefix),
 Posix 2008 requires that @command{make} must invoke each command with
 the equivalent of a @samp{sh -e -c} subshell, which causes the
 subshell to exit immediately if a subsidiary simple-command fails,
-although not all @command{make} implementations have historically
+with some complicated exceptions.
+Historically not all @command{make} implementations
 followed this rule.  For
 example, the command @samp{touch T; rm -f U} may attempt to
 remove @file{U} even if the @command{touch} fails, although this is not
@@ -20428,6 +20433,24 @@ are worried
 about porting to buggy BSD shells it may be simpler to migrate
 complicated @command{make} actions into separate scripts.
 
+@node Command Line Prefixes
+@section Makefile Command Line Prefixes
+
+Makefile command lines can be preceded by zero or more of
+the command line prefixes @samp{-}, @samp{@@}, and @samp{+},
+which modify how @command{make} processes the command.
+Although Posix says these are the only command line prefixes,
+some @command{make} implementations, such as Solaris @command{make},
+support the additional prefixes @samp{!} and @samp{?}.
+Portable makefiles should therefore avoid using these two characters at
+the start of a makefile command line.
+For example:
+
+@example
+mishandled-by-Solaris-make:; ! grep FIXME foo.c
+portable-to-Solaris-make:; :;! grep FIXME foo.c
+@end example
+
 @node Special Chars in Names
 @section Special Characters in Make Macro Names