Re: [PATCH 2/3] cmake: create compile_commands.json by default

From: Matt Rogers <mattr94@gmail.com>
Date: Jun 5, 2021, 22:36 UTC
Message-ID: <CAOjrSZsyUi+RAqxXyd6JqzWqO8hMdtwTuWpZy+cKbz654Xu45A@mail.gmail.com>
In-Reply-To: <CAKiG+9W8Da4bG87VjTKN6m=cX+v_x33YAw8p4MqCfmNinYt1XA@mail.gmail.com>

On Fri, Jun 4, 2021 at 5:09 PM Sibi Siddharthan <sibisiddharthan.github@gmail.com> wrote:

Show 33 quoted lines

>
> On Fri, Jun 4, 2021 at 11:13 PM Matthew Rogers via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
> >
> > A straightforward way to accomplish this is to make it as simple as
> > possible is to enable the generation of the compile_commands.json file,
> > which is supported by many tools such as: clang-tidy, clang-format,
> > sourcetrail, etc.
> >
> > This does come with a small run-time overhead during the configuration
> > step (~6 seconds on my machine):
> >
> >     Time to configure with CMAKE_EXPORT_COMPILE_COMMANDS=TRUE
> >
> >     real    1m9.840s
> >     user    0m0.031s
> >     sys     0m0.031s
> >
> >     Time to configure with CMAKE_EXPORT_COMPILE_COMMANDS=FALSE
> >
> >     real    1m3.195s
> >     user    0m0.015s
> >     sys     0m0.015s
> >
> > This seems like a small enough price to pay to make the project more
> > accessible to newer users.  Additionally there are other large projects
> > like llvm [2] which has had this enabled by default for >6 years at the
> > time of this writing, and no real negative consequences that I can find
> > with my search-skills.
> >
>
> The overhead is actually much smaller than that. In my system it is
> less than 150ms.

Is that 150 ms for the whole process or just the difference between the two options? I'm running this on windows via the git bash provided by the git sdk.

> The first configure takes this long because we generate command-list.h
> and config-list.h.
> This process is really slow under Windows.
>

I used two different build directories for both my invocations specifically to avoid having to account for cache variables and other side effects from earlier configurations. The variation could also be from network latency since in this test I was downloading vcpkg, etc.

> Thank You,
> Sibi Siddharthan

-- 
Matthew Rogers