using iwyu (include-what-you-use) to analyze includes (was: [PATCH] bisect.c: remove unused includes)
On Thu, Mar 31 2022, Junio C Hamano wrote:
[Changed $subject to make this easier to find]
Show 24 quoted lines
> Garrit Franke <garrit@slashdev.space> writes:
>
>> Clean up includes no longer needed by bisect.c.
>>
>> Signed-off-by: Garrit Franke <garrit@slashdev.space>
>> ---
>> bisect.c | 9 ---------
>> 1 file changed, 9 deletions(-)
>>
>> diff --git a/bisect.c b/bisect.c
>> index 9e6a2b7f20..e07e2d215d 100644
>> --- a/bisect.c
>> +++ b/bisect.c
>> @@ -1,21 +1,12 @@
>> -#include "cache.h"
>
> cf. Documentation/CodingGuidelines
>
> The first #include must be <git-compat-util.h>, or <cache.h> or
> <builtin.h>, which are well known to include <git-compat-util.h>
> first.
>
> Including <git-compat-util.h> indirectly by <config.h> ->
> <hashmap.h> -> <hash.h> -> <git-compat-util.h> does not count.
Also: Some built-ins don't include builtin.h as they should, a fix (or
even basic CI check) for that would be most welcome.
git grep -C2 -n -F -e builtin.h -e cache.h -e git-compat-util.h -- builtin
I.e. we have this saying a lot of those are redundant:
Documentation/CodingGuidelines- - The first #include in C files, except in platform specific compat/
Documentation/CodingGuidelines- implementations, must be either "git-compat-util.h", "cache.h" or
Documentation/CodingGuidelines: "builtin.h". You do not have to include more than one of these.
But maybe it's not worth it, anyway...
Show 21 quoted lines
>> #include "config.h"
>> -#include "commit.h"
>
> Other headers may indirectly include <commit.h> as their
> implementation detail, but what matters is that *we* in this source
> file use what <commit.h> gives us ourselves, like the concrete shape
> of "struct commit_list". This change is not wanted.
>
> I'll stop here. There may be truly leftover "unused" includes among
> those removed by the remainder of this patch, but I suspect that
> some are like <commit.h> above, i.e. we directly use it, and because
> we do not want to be broken by some header file's implementation
> detail changing, we MUST include it ourselves.
>
> I think this should give us a useful guideline to sift through the
> rest, and an updated patch to remove truly unused ones are very much
> welcome. We may actually find some we are not directly including
> ourselves but we should (e.g. I do not see <string-list.h> included
> by us, but we clearly use structures and functions declared there,
> and probably is depending, wrongly, on some header file we include
> happens to indirectly include it).
... For anyone interested in pursuing this, I think using the excellent include-what-you-use tool would be a nice start.
We could even eventually add it to our CI if the false positive rate isn't bad (I haven't checked much): https://github.com/include-what-you-use/include-what-you-use
E.g. in this case (I manually omitted the rest of the output, there's probably a iwyu option to omit it, but I didn't see how do that from skimming the docs):
$ sudo apt install iwyu # YMMV
$ make bisect.o CC=include-what-you-use CFLAGS="-Xiwyu --verbose=1" 2>&1 | grep -v -E -e '^#include <' -e '^#include "(cache|git-compat-util|gettext)\.h"'
CC bisect.o
(bisect.h has correct #includes/fwd-decls)
bisect.c should add these lines:
#include "hash.h" // for oideq, object_id, oidcmp, oidcpy, GIT_...
#include "object.h" // for object, repo_clear_commit_marks
#include "path.h" // for GIT_PATH_FUNC, git_pathdup
#include "pretty.h" // for CMIT_FMT_UNSPECIFIED, format_commit_me...
#include "repository.h" // for repository (ptr only), the_repository
#include "strbuf.h" // for strbuf_release, strbuf, strbuf_getline_lf
#include "string-list.h" // for string_list_append, string_list_clear
bisect.c should remove these lines:
- #include "hash-lookup.h" // lines 9-9
- struct commit_weight; // lines 76-76
Then if I patch it as:
diff --git a/bisect.c b/bisect.c
index 9e6a2b7f201..512430e3cc8 100644
--- a/bisect.c
+++ b/bisect.c
@@ -6,7 +6,6 @@
#include "refs.h"
#include "list-objects.h"
#include "quote.h"
-#include "hash-lookup.h"
#include "run-command.h"
#include "log-tree.h"
#include "bisect.h"
@@ -16,6 +15,13 @@
#include "commit-reach.h"
#include "object-store.h"
#include "dir.h"
+#include "hash.h"
+#include "object.h"
+#include "path.h"
+#include "pretty.h"
+#include "repository.h"
+#include "strbuf.h"
+#include "string-list.h"
static struct oid_array good_revs;
static struct oid_array skipped_revs;
It's happier, but probably needs to be told to ignore define_commit_slab() somehow:
$ make bisect.o CC=include-what-you-use CFLAGS="-Xiwyu --verbose=1" 2>&1 | grep -v -E -e '^#include <' -e '^#include "(cache|git-compat-util|gettext)\.h"'
CC bisect.o
(bisect.h has correct #includes/fwd-decls)
bisect.c should add these lines:
bisect.c should remove these lines:
- struct commit_weight; // lines 82-82
That still needs to be massaged a bit, e.g. we should probably omit hash.h and anything else in cache.h and git-compat-util.h.
Or maybe not & we should make those headers even lighter. It is rather annoying that changing some of those things leads to a complete re-build, but there's a trade-off there where we probably want things like gettext.h and other used-almost-everywhere headers in included by those.
So take all the above with a huge grain of salt. I haven't used iwyu much, but it seems to be something that'll help us go in the direction Junio noted above.
I think starting with:
make -k git-objs <the CC etc. params above>
And tackling the "should remove these lines" issues first would be a
good start, e.g. for serve.c it says:
serve.c should remove these lines:
- #include "cache.h" // lines 1-1
- #include "strvec.h" // lines 6-6
We don't want that first one, but it's right about the second one. It's been orphaned since f0a35c9ce52 (serve: drop "keys" strvec, 2021-09-15), I skimmed some of the rist and they all seem like good suggestions. E.g. lockfile.h for builtin/apply.c, which isn't needed since 6d058c88264 (apply: move lockfile into `apply_state`, 2017-10-05).
Garrit Franke
