t/spy-double-colon.sh

   1 #! /bin/sh
   2 # Copyright (C) 2003-2024 Free Software Foundation, Inc.
   3 #
   4 # This program is free software; you can redistribute it and/or modify
   5 # it under the terms of the GNU General Public License as published by
   6 # the Free Software Foundation; either version 2, or (at your option)
   7 # any later version.
   8 #
   9 # This program is distributed in the hope that it will be useful,
  10 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 # GNU General Public License for more details.
  13 #
  14 # You should have received a copy of the GNU General Public License
  15 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
  16
  17 # Check whether double colon rules work.  The Unix V7 make manual
  18 # mentions double-colon rules, but POSIX does not.  They seem to be
  19 # supported by all Make implementation as far as we can tell. This test
  20 # case is a spy: we want to detect if there exist implementations where
  21 # these do not work.  We might use these rules to simplify the rebuild
  22 # rules (instead of the $? hack).
  23
  24 # Tom Tromey write:
  25 # | In the distant past we used :: rules extensively.
  26 # | Fran?ois convinced me to get rid of them:
  27 # |
  28 # | Thu Nov 23 18:02:38 1995  Tom Tromey  <tromey@cambric>
  29 # | [ ... ]
  30 # |         * subdirs.am: Removed "::" rules
  31 # |         * header.am, libraries.am, mans.am, texinfos.am, footer.am:
  32 # |         Removed "::" rules
  33 # |         * scripts.am, programs.am, libprograms.am: Removed "::" rules
  34 # |
  35 # |
  36 # | I no longer remember the rationale for this.  It may have only been a
  37 # | belief that they were unportable.
  38
  39 # On a related topic, the Autoconf manual has the following text:
  40 # |     'VPATH' and double-colon rules
  41 # |           Any assignment to 'VPATH' causes Sun 'make' to only execute
  42 # |           the first set of double-colon rules.  (This comment has been
  43 # |           here since 1994 and the context has been lost.  It's probably
  44 # |           about SunOS 4.  If you can reproduce this, please send us a
  45 # |           test case for illustration.)
  46
  47 # We already know that overlapping ::-rule like
  48 #
  49 #   a :: b
  50 #       echo rule1 >> $@
  51 #   a :: c
  52 #       echo rule2 >> $@
  53 #   a :: b c
  54 #       echo rule3 >> $@
  55 #
  56 # do not work equally on all platforms.  It seems that in all cases
  57 # Make attempts to run all matching rules.  However at least GNU Make,
  58 # NetBSD Make, and FreeBSD Make will detect that $@ was updated by the
  59 # first matching rule and skip remaining matches (with the above
  60 # example that means that unless 'a' was declared PHONY, only "rule1"
  61 # will be appended to 'a' if both b and c have changed).  Other
  62 # implementations like OSF1 Make and HP-UX Make do not perform such a
  63 # check and execute all matching rules whatever they do ("rule1",
  64 # "rule2", abd "rule3" will all be appended to 'a' if b and c have
  65 # changed).
  66
  67 # So it seems only non-overlapping ::-rule may be portable.  This is
  68 # what we check now.
  69
  70 . test-init.sh
  71
  72 cat >Makefile <<\EOF
  73 a :: b
  74         echo rule1 >> $@
  75 a :: c
  76         echo rule2 >> $@
  77 EOF
  78
  79 touch b c
  80 $sleep
  81 : > a
  82 $MAKE
  83 test x"$(cat a)" = x
  84 $sleep
  85 touch b
  86 $MAKE
  87 test "$(cat a)" = "rule1"
  88 # Ensure a is strictly newer than b, so HP-UX make does not execute rule2.
  89 $sleep
  90 : > a
  91 $sleep
  92 touch c
  93 $MAKE
  94 test "$(cat a)" = "rule2"
  95
  96 # Unfortunately, the following is not portable to FreeBSD/NetBSD/OpenBSD
  97 # make, see explanation above.
  98
  99 #: > a
 100 #$sleep
 101 #touch b c
 102 #$MAKE
 103 #grep rule1 a
 104 #grep rule2 a
 105
 106 :