branch-1-7: lib/am/yacc.am: never redirect directly to $@

[Jim Meyering]

This patch is for the 1.7 branch, but I'll install it on
the trunk too, unless someone objects.

There are two important rules in writing Makefiles:
  * never redirect directly to $@
  * when you do update $@, do it atomically and only after any side-effect
      commands have completed successfully

In the patch below, %OBJ% usually expands to address@hidden

2003-04-17  Jim Meyering  <address@hidden>

        * lib/am/yacc.am (?GENERIC?%EXT%%DERIVED-EXT% aka .y.c): Don't redirect
        directly to address@hidden  Instead, redirect to address@hidden and 
rename upon success.
        Also, move the commands that update $@ so they are last.  Otherwise,
        this rule could leave the user with an up to date target (.c file)
        but with a missing or corrupted corresponding .h file.

Index: lib/am/yacc.am
===================================================================
RCS file: /cvs/automake/automake/lib/am/yacc.am,v
retrieving revision 1.14
diff -u -p -r1.14 yacc.am
--- lib/am/yacc.am      8 Jun 2002 17:22:27 -0000       1.14
+++ lib/am/yacc.am      17 Apr 2003 19:51:05 -0000
@@ -1,5 +1,5 @@
 ## automake - create Makefile.in from Makefile.am
-## Copyright 1998, 1999, 2001  Free Software Foundation, Inc.
+## Copyright 1998, 1999, 2001, 2003  Free Software Foundation, Inc.
 
 ## This program is free software; you can redistribute it and/or modify
 ## it under the terms of the GNU General Public License as published by
@@ -22,9 +22,6 @@ if %?MORE-THAN-ONE%
        $(SHELL) $(YLWRAP) `test -f '%SOURCE%' || echo '$(srcdir)/'`%SOURCE% 
y.tab.c %OBJ% y.tab.h %BASE%.h y.output %BASE%.output -- %COMPILE%
 else !%?MORE-THAN-ONE%
        %COMPILE% `test -f '%SOURCE%' || echo '$(srcdir)/'`%SOURCE%
-## Edit out `#line' or `#' directives.
-       sed '/^#/ s|y\.tab\.c|%OBJ%|' y.tab.c >%OBJ%
-       rm -f y.tab.c
 ## Edit out Bison multiple inclusion guards.  It may be BISON_Y_TAB_H,
 ## or Y_TAB_H depending upon the version, that's why the regexp is
 ## so loose.
@@ -43,4 +40,7 @@ else !%?MORE-THAN-ONE%
        if test -f y.output; then \
          mv y.output %BASE%.output; \
        fi
+## Edit out `#line' or `#' directives.
+       sed '/^#/ s|y\.tab\.c|%OBJ%|' y.tab.c >%OBJ%t && mv %OBJ%t %OBJ%
+       rm -f y.tab.c
 endif !%?MORE-THAN-ONE%