[cfe-dev] Getting involved with Clang refactoring

[Manuel Klimek]

On Tue, May 22, 2012 at 3:19 PM, James K. Lowden
<jklowden at schemamania.org> wrote:
> On Mon, 21 May 2012 10:56:51 -0700
> Douglas Gregor <dgregor at apple.com> wrote:
>
>> > And while I'm at it. One thing that might be interesting for a
>> > contribution is getting the compilation database support up for
>> > libclang
> ...
>> That's a good idea. libclang assumes that you have your own
>> compilation database (or similar) and that you use it up feed command
>> lines to libclang, but it would be easier to use libclang if we could
>> just point it at a build or source tree and then feed source files to
>> libclang.
>
> Gentlemen, could you tell me please what you mean by a "compilation
> database"?  It sounds like a list of files to compile, something I'd
> normally look to make(1) to provide.  Apparently that's not what you
> mean, or there's some reason make won't do the job.
>
> If I understood the problem better perhaps there's something I could do
> about it.

The problem with make is that it executes the compiler based on
changes in the dependency graph.

Imagine you want to run a tool on all files that use a specific
symbol. To do this you need to:
1. figure out the compile command line for the file into which you're
pointing to figure out the symbol under the cursor
2. run the tool over all files that reference that symbol

Both steps are completely independent of any dependency changes, so
running the tool as part of make / as a clang plugin is not the best
option here. You want a compilation database out of which you can
quickly (for interactive use cases) get the compile command line for
any file in a project.

LibTooling has this idea already at its core:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Tooling/CompilationDatabase.h?view=markup

You first generate a compilation database, and then feed that into
your tool run.

The idea would be to wrap up the CompilationDatabase in a stable C
interface in libclang, and provide parsing functions in libclang that
take the C-equivalent of a CompilationDatabase instead of the command
line itself.

Thoughts?
/Manuel