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

[Philippe Blain <levraiphilippeblain@gmail.com>]

Hi Brian, 

> Le 30 août 2020 à 18:10, brian m. carlson <sandals@crustytoothpaste.net> a écrit :
> 
> 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.
> 
> So I'm very much in favor of a change like this.

Thanks!

> 
>> +ifeq ($(GENERATE_COMPILATION_DATABASE),yes)
>> +all:: compile_commands.json
>> +compile_commands.json:
>> +	@$(RM) $@
>> +	$(QUIET_GEN)sed -e '1s/^/[/' -e '$$s/,$$/]/' $(compdb_dir)*.o.json > $@+
>> +	@if test -s $@+; then mv $@+ $@; else $(RM) $@+; fi
>> +endif
> 
> How are those commas at the end of the line added?  Are they natively
> part of the files?  If so, this seems reasonable.

Yes: the '*.o.json' files generated by the compiler contain one JSON object per file, 
with a trailing comma.
This 'sed' invocation turns these files into a proper JSON array by:
- adding a '[' at the beginning and a ']' at the end of the list of objects
- removing the comma after the last entry (before the closing ']')