Re: [PATCH v2] Record dependencies during build instead of before

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+From: Tomi Ollila <tomi.ollila@iki.fi>\r
+To: Austin Clements <amdragon@MIT.EDU>, notmuch@notmuchmail.org\r
+Subject: Re: [PATCH v2] Record dependencies during build instead of before\r
+In-Reply-To: <1334176719-24781-1-git-send-email-amdragon@mit.edu>\r
+References: <1333857710-24511-1-git-send-email-amdragon@mit.edu>\r
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+Date: Wed, 11 Apr 2012 23:52:01 +0300\r
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+\r
+On Wed, Apr 11 2012, Austin Clements <amdragon@MIT.EDU> wrote:\r
+\r
+> Previously, the makefile created dependency files in a separate, first\r
+> pass.  In particular, include-ing the dependency files would cause\r
+> make to attempt to rebuild those files using the dependency-generation\r
+> rules in the makefile.  Unfortunately, this approach required obtuse\r
+> rules and silently delayed the start of the build process (by quite a\r
+> bit on a clean tree without any dependency files).  Worse, this\r
+> required the dependency files to themselves depend on all of the\r
+> headers the source file depended on, which meant that, if a header\r
+> file was removed, the depedency file could not be updated because of a\r
+> missing dependency (!), which would cause make to silently fail.\r
+>\r
+> This patch eliminates the dependency generation rules and instead\r
+> generates dependency files as a side-effect of the regular build rule.\r
+> On the first build, we don't need to know the dependencies beforehand;\r
+> the object file doesn't exist, so it will be built anyway.  On\r
+> subsequent builds, if a header file is updated, the dependency rules\r
+> generated by the previous build will force a rebuild.  If a source\r
+> file is updated, the dependency rules may be stale, but it doesn't\r
+> matter because the updated source file will force a rebuild.\r
+>\r
+> In the final case above, the stale dependency rules may refer to a\r
+> header file that no longer exists but is also no longer needed.  In\r
+> order to prevent this from breaking the build, we also pass gcc the\r
+> -MP option, which generates phony targets for every depended-on header\r
+> file, so make won't complain if it can't find them during a later\r
+> build.\r
+> ---\r
+\r
+Looks good, patch applies and works (at least the cases I tested and\r
+examined). And is definitely better than before.\r
+\r
++1\r
+\r
+Tomi \r
+\r
+> Sorry, the previous version of this patch was corrupted.  Hopefully\r
+> this one will be correct.\r
+>\r
+>  Makefile.local |   18 ++++--------------\r
+>  1 files changed, 4 insertions(+), 14 deletions(-)\r
+>\r