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22 Fri, 14 Feb 2014 21:24:15 +0200 (EET)
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23 From: Tomi Ollila <tomi.ollila@iki.fi>
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24 To: Austin Clements <amdragon@MIT.EDU>
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25 Subject: Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is
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27 In-Reply-To: <20140213074944.GY4375@mit.edu>
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28 References: <1390645309-2326-1-git-send-email-tomi.ollila@iki.fi>
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29 <20140213071026.GX4375@mit.edu> <m2sirn1nik.fsf@guru.guru-group.fi>
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30 <20140213074944.GY4375@mit.edu>
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36 Date: Fri, 14 Feb 2014 21:24:15 +0200
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37 Message-ID: <m2bny9ebvk.fsf@guru.guru-group.fi>
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55 On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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57 > Quoth Tomi Ollila on Feb 13 at 9:26 am:
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58 >> On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:
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60 >> > Quoth Tomi Ollila on Jan 25 at 12:21 pm:
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61 >> >> So that the target is newer than its prerequisites.
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63 >> >> emacs/Makefile.local | 3 +--
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64 >> >> 1 file changed, 1 insertion(+), 2 deletions(-)
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66 >> >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local
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67 >> >> index 42bfbd9..d5d402e 100644
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68 >> >> --- a/emacs/Makefile.local
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69 >> >> +++ b/emacs/Makefile.local
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70 >> >> @@ -32,8 +32,7 @@ emacs_bytecode = $(emacs_sources:.el=.elc)
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71 >> >> ifeq ($(HAVE_EMACS),1)
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72 >> >> $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
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73 >> >> $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
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74 >> >> - -f batch-make-deps $(emacs_sources) > $@.tmp && \
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75 >> >> - (cmp -s $@.tmp $@ || mv $@.tmp $@)
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76 >> >> + -f batch-make-deps $(emacs_sources) > $@.tmp && mv $@.tmp $@
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77 >> >> -include $(dir)/.eldeps
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79 >> >> CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
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81 >> > Is this just so the rule doesn't get run again on the next make
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82 >> > invocation (unless, of course, a dependent changed)?
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84 >> Basically yes. I did multiple builds in rapid succession when developing
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85 >> something and this thing confused me quite a lot in the beginning...
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87 >> > Interestingly, if any of the dependents have changed, but in ways that
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88 >> > don't affect .eldeps, this change will make the build more expensive
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89 >> > because it will trigger a make restart after .eldeps is updated.
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91 >> I wondered what was the reason for the recipe you've chosen here, has
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92 >> it something to do with inodes or something ;) (and were going to ask
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93 >> an alternative to touch (or even : > $@) the target...
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95 >> ... but now I understand. E.g. change in notmuch-lib.el will cause *all*
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96 >> .el files to be re-bytecompiled after this change.
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98 > This is unrelated to the cmp in the recipe. A change in
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99 > notmuch-lib.el *must* cause almost all .el files to be recompiled
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100 > because they almost all require it and may use macros from it. If you
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101 > touch, e.g., notmuch-hello.el, you'll see that very little is rebuilt
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102 > (with or without this patch).
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104 >> An alternative to this patch would be adding a message to the rule
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105 >> which informs user to touch .eldeps to avoid re-doing .eldeps if
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106 >> that irritates one :D
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110 >> (cmp -s $@.tmp $@ && \
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111 >> echo "touch $@ to avoid redoing this target" || mv $@.tmp $@)
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113 > I think this patch is good as it is; I was just pointing out that the
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114 > change also has a performance drawback in some situations. (Knowing
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115 > make, there's probably *some* way to get the best of both worlds and
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116 > it's probably really ugly.)
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118 Ah, now I understand, because emacs/Makefile.local includes emacs/.eldeps
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119 when it notices mtime of emacs/.eldeps changes it restarts itself...
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121 ... to compare with current behaviour:
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125 $ touch emacs/notmuch.el
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129 Use "make V=1" to see the verbose compile lines.
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130 EMACS emacs/.eldeps
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131 make: Nothing to be done for `all'.
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133 Use "make V=1" to see the verbose compile lines.
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134 EMACS emacs/.eldeps
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135 make: Nothing to be done for `all'.
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137 Use "make V=1" to see the verbose compile lines.
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138 EMACS emacs/.eldeps
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139 make: Nothing to be done for `all'.
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141 It will rerun emacs -L emacs -batch -l make-deps.el -f batch-make-deps ...
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142 over and over again...
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144 I thought I figured out a solution involving .eldeps.stamp file but
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145 that turned out to be no-go... (circular dependency netween .eldeps.stamp
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146 and Makefile.local).
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148 So, with this if one edits emacs/* files and keeps building byte-compiled
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149 versions often, make will both run EMACS emacs/.eldeps and restarting
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150 -- and when moving to edit other files both of the above stops. Without
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151 this change after editing emacs/* files EMACS emacs/.eldeps will be
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152 executed until it is touched or make clean executed (I wonder how make
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153 handles rebuilding emacs/.eldeps while doing make clean ;)
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