Re: [PATCHv3 1/6] Add missing includes and forward declares

[Elijah Newren <newren@gmail.com>]

On Tue, Aug 14, 2018 at 10:10 PM Jonathan Nieder <jrnieder@gmail.com> wrote:
>
> Elijah Newren wrote:
>
> > Subject: Add missing includes and forward declares
>
> nit: s/declares/declarations/

Thanks.

> This is a huge patch.  Was it autogenerated or generated manually?
> Can the commit message say something about methodology?

Mostly manually.  I had a simple program that would create a dummy.c
file that included git-compat-util.h then exactly one header, compile
it, and spit any compile errors at me.  I repeated that through the
top-level headers.

I didn't want to repeat that description in all 6 patches, since all
six came from that, so I put it in the cover letter.  Since patch #1
has most that changes though, I guess it makes sense to include it at
least in that one?

> Is there an easy way to review it?  (Keep in mind that I'm super lazy.
> ;-))

I guess I could send you my hacky python script that loops through the
top-level header files and creates the dummy two-line c file, and you
could inspect it and run it.  But that only verifies that it compiles,
not that the changes I choose are "correct".

>
> > Signed-off-by: Elijah Newren <newren@gmail.com>
> > ---
> [...]
> > --- a/alloc.h
> > +++ b/alloc.h
> > @@ -1,9 +1,11 @@
> >  #ifndef ALLOC_H
> >  #define ALLOC_H
> >
> > +struct alloc_state;
> >  struct tree;
> >  struct commit;
> >  struct tag;
> > +struct repository;
> >
> >  void *alloc_blob_node(struct repository *r);
>
> That's reasonable.  Going forward, is there a way to tell if some of
> these forward declarations are no longer needed at some point in the
> future (e.g. can clang be convinced to warn us about it)?

I'm not aware of anything currently; while I could have easily missed
things, projects like
https://github.com/include-what-you-use/include-what-you-use (which
look active and have a July 2018 date on them) make me suspect there
isn't a good answer currently.

> [...]
> > --- a/apply.h
> > +++ b/apply.h
> > @@ -1,6 +1,9 @@
> >  #ifndef APPLY_H
> >  #define APPLY_H
> >
> > +#include "lockfile.h"
> > +#include "string-list.h"
> > +
> >  enum apply_ws_error_action {
>
> Here, to avoid strange behavior, we have to be careful to make sure
> the headers don't #include apply.h back.  It's a pretty high-level
> header so there's no risk of that *phew*.

:-)

> [...]
> > --- a/archive.h
> > +++ b/archive.h
> > @@ -3,6 +3,9 @@
> >
> >  #include "pathspec.h"
> >
> > +struct object_id;
> > +enum object_type;
>
> enums are of unknown size, so forward declarations don't work for
> them.  See bb/pedantic for some examples.

structs are also of unknown size; the size is irrelevant when the
function signature merely uses a pointer to the struct or enum.  The
enum forward declaration fixes a compilation bug.

> enum object_type is defined in cache.h, so should this #include that?

We could, but we don't need the definition; a forward declaration is sufficient.

> [...]
> > --- a/commit-graph.h
> > +++ b/commit-graph.h
> > @@ -4,6 +4,7 @@
> >  #include "git-compat-util.h"
> >  #include "repository.h"
> >  #include "string-list.h"
> > +#include "cache.h"
>
> We can skip the #include of git-compat-util.h since all .c files
> include it.

Good point.  Should I go through and remove all the inclusions of
git-compat-util.h in header files?

> [...]
> > --- a/fsmonitor.h
> > +++ b/fsmonitor.h
> > @@ -1,6 +1,13 @@
> >  #ifndef FSMONITOR_H
> >  #define FSMONITOR_H
> >
> > +#include "cache.h"
> > +#include "dir.h"
> > +
> > +struct cache_entry;
> > +struct index_state;
> > +struct strbuf;
>
> cache_entry et al are defined in cache.h, right?  Are these forward
> decls needed?

Good catch; they can be removed.  I'm pretty sure I added the forward
declarations first, then noticed it wasn't enough, added the cache.h
include, and forgot to clean up.

> [...]
> > --- a/merge-recursive.h
> > +++ b/merge-recursive.h
> > @@ -1,8 +1,10 @@
> >  #ifndef MERGE_RECURSIVE_H
> >  #define MERGE_RECURSIVE_H
> >
> > -#include "unpack-trees.h"
> >  #include "string-list.h"
> > +#include "unpack-trees.h"
>
> just curious, no need to change: where does this reordering come from?

Well, since I was manually editing anyway, I saw these and decided to
alphabetize it since it's a file I deal with a lot.  *shrug*

> [...]
> > --- a/pathspec.h
> > +++ b/pathspec.h
> > @@ -1,6 +1,11 @@
> >  #ifndef PATHSPEC_H
> >  #define PATHSPEC_H
> >
> > +#include "string.h"
> > +#include "strings.h"
>
> What are these headers?

The original patch[1] had explanations of why I added them:

+#include "string.h"   /* For str[n]cmp */
+#include "strings.h"  /* For str[n]casecmp */

But Peff requested that I remove the comments.

[1] https://public-inbox.org/git/20180811043218.31456-2-newren@gmail.com/

> The rest looks good.
>
> Thanks and hope that helps,
> Jonathan

Thanks for taking a look!