Re: [PATCH] Makefile: add support for generating JSON compilation database

From: Philippe Blain <levraiphilippeblain@gmail.com>
Date: Sep 1, 2020, 13:18 UTC
Message-ID: <867D6718-E377-47B8-BD32-0800872B3DE0@gmail.com>
In-Reply-To: <20200901073827.GA3967005@coredump.intra.peff.net>

Show 28 quoted lines

> Le 1 sept. 2020 à 03:38, Jeff King <peff@peff.net> a écrit :
> 
> On Sun, Aug 30, 2020 at 09:24:03PM -0700, Junio C Hamano wrote:
> 
>> "brian m. carlson" <sandals@crustytoothpaste.net> writes:
>> 
>>> On 2020-08-30 at 19:28:27, Philippe Blain via GitGitGadget wrote:
>>>> From: Philippe Blain <levraiphilippeblain@gmail.com>
>>>> 
>>>> Tools based on LibClang [1] can make use of a 'JSON Compilation
>>>> Database' [2] that keeps track of the exact options used to compile a set
>>>> of source files.
>>> 
>>> For additional context why this is valuable, clangd, which is a C
>>> language server protocol implementation, can use these files to
>>> determine the flags needed to compile a file so it can provide proper
>>> editor integration.  As a result, editors supporting the language server
>>> protocol (such as VS Code, or Vim with a suitable plugin) can provide
>>> better searching, integration, and refactoring tools.
>> 
>> I found that the proposed commit log was very weak to sell the
>> change; some of what you gave above should definitely help strenthen
>> it.
> 
> Likewise. Looking at the output, I'm confused how it would help with
> things like searching and refactoring. It might be nice to spell it out
> for those of us exposed to it for the first time (I tried following the
> links but remained unenlightened).

OK, I'll improve the commit message. I'm not at all an expert in this subject, I just had to generate a compilation database myself to use the Sourcetrail source explorer [1] with Git so I figured I'd share what I had done. Further exploration of the topic are in [2] and [3]. Note that I did try some of the tools listed in [2] before resorting to modifying the Makefile, but these tools either did not work at all or produced wrong output (ex. strings in the JSON were not properly quoted, etc.)

> I'd also be curious to hear what advantages it gives to add a new
> Makefile knob rather than just letting interested parties add -MJ to
> their CFLAGS. Is it just a convenience to create the concatenated form?

Unfortunately this would not work because the '-MJ' flag needs a file name to know where to put the JSON fragment.

Thanks, Philippe.

[1] www.sourcetrail.com [2] https://sarcasm.github.io/notes/dev/compilation-database.html [3] https://eli.thegreenplace.net/2014/05/21/compilation-databases-for-clang-based-tools