Re: [PATCH] Makefile: drop GEN_HDRS

[Jeff King <peff@peff.net>]

On Fri, Dec 13, 2019 at 03:25:41PM -0800, Junio C Hamano wrote:

> Get rid of GEN_HDRS, which is used only once to list the headers we
> do not run hdr-check test on, and instead explicitly list that the
> ones, either tracked or generated, that we exempt from the test.

Yeah, I think this is an improvement by itself.

After reading this, though:

>  - If we value the header cleanliness check, we eventually want to
>    teach our header generating scripts to produce clean headers.
>    Keeping the blanket "generated headers can be left as dirty as we
>    want" exception does not nudge us in the right direction.

I did expect to see the actual hdr-check behavior move towards checking
these generated versions. However, both are kind of interesting.

unicode-width.h isn't a "real" header file; it's meant to be included in
the middle of a function. I think it _could_ be changed to define
"struct interval" itself, and then be a static file-scope variable. But
there's not really a compelling reason to do so.

But "command-list.h" is more of a traditional header file, being
included at the top of help.c. In theory the hdr-check target could add
a dependency on it, and then we could check it along with everything
else. But even without that first step, if I remove it from EXCEPT_HDRS,
nothing happens!

That's because LIB_H is created by running find in the local filesystem.
So until it's generated, we don't realize it's there to check. I kind of
wonder if it should be part of LIB_H. I suspect that on some systems,
we'd fail to notice a rebuild when command-list.txt is updated (but
nobody noticed, because it is only systems that do not have
compiler-supported dependency tracking, and most developers are no
modern platforms that do).

-Peff