Re: Unused #include statements

Jeff King [off-list ref] writes:

On Thu, Jan 15, 2015 at 10:50:45AM -0800, Junio C Hamano wrote:

quoted

 ...
Thoughts?  I am not looking forward to a torrent of patches whose
sole purpose is to make the existing C files conform to any such
rule, though.  Clean-up patches that trickle in at a low rate is
tolerable, but a torrent is too distracting.

I don't think the "optionally" one above is that necessary. Not because
I don't agree with it, but because I do not know that we want to get
into the business of laying out every minute detail and implication.
The CodingGuidelines document is meant to be guidelines, and I do not
want to see arguments like "well, the guidelines do not explicitly
_disallow_ this, so you must accept it or add something to the
guideline". That is a waste of everybody's time.

Totally.  I know we do not want to get into that business.

A general philosophy + good taste (from the submitter and the
maintainer) should ideally be enough.

Yes, "ideally" ;-)

Which isn't to say we shouldn't clarify the document when need be. But I
think what I quoted at the top already is probably a good improvement
over what is there.

OK, thanks.  Let's queue something like this for post 2.3 cycle,
then.

-- >8 --
Subject: CodingGuidelines: clarify C #include rules

Even though "advice.h" includes "git-compat-util.h", it is not
sensible to have it as the first #include and indirectly satisify
the "You must give git-compat-util.h a clean environment to set up
feature test macros before including any of the system headers are
included", which is the real requirement.

Because:

 - A command that interacts with the object store, config subsystem,
   the index, or the working tree cannot do anything without using
   what is declared in "cache.h";

 - A built-in command must be declared in "builtin.h", so anything
   in builtin/*.c must include it;

 - These two headers both include "git-compat-util.h" as the first
   thing; and

 - Almost all our *.c files (outside compat/ and borrowed files in
   xdiff/) need some Git-ness from "cache.h" to do something
   Git-ish.

let's explicitly specify that one of these three header files must
be the first thing that is included.

Any of our *.c file should include the header file that directly
declares what it uses, instead of relying on the fact that some *.h
file it includes happens to include another *.h file that declares
the necessary function or type.  Spell it out as another guideline
item.

Helped-by: Jeff King [off-list ref]
Signed-off-by: Junio C Hamano <redacted>
---
 Documentation/CodingGuidelines | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index 894546d..578d07c 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines

@@ -328,9 +328,14 @@ For C programs:
 
  - When you come up with an API, document it.
 
- - The first #include in C files, except in platform specific
-   compat/ implementations, should be git-compat-util.h or another
-   header file that includes it, such as cache.h or builtin.h.
+ - The first #include in C files, except in platform specific compat/
+   implementations, must be either "git-compat-util.h", "cache.h" or
+   "builtin.h".  You do not have to include more than one of these.
+
+ - A C file must directly include the header files that declare the
+   functions and the types it uses, except for the functions and types
+   that are made available to it by including one of the header files
+   it must include by the previous rule.
 
  - If you are planning a new command, consider writing it in shell
    or perl first, so that changes in semantics can be easily