[cfe-dev] Getting involved with Clang refactoring

[James K. Lowden]

On Tue, 22 May 2012 15:49:42 +0200
Manuel Klimek <klimek at google.com> wrote:

> > 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

3.  In an order determined by the dependency graph.  :-) 

Thank you for the explanation.  At least now I partly understand what
you're talking about.  

But I'm still puzzled.  Why would one need to recompile all files that
use a specific symbol? Changes to a symbol normally occur in a header
file, affecting the dependency graph in just the way that makes make
useful.  To solve the problem you describe -- to have Clang recompile
"all files that use a specific symbol"  -- one could touch(1) all such
files and then run make.  

The "figure out the command line" part is also intrinsic to make, as
you know, based on the filename suffix.  That's 30 years of prior art
that the compilation database seems to be reinventing.  

I understand the project has an existing build infrastructure, and that
the compilation database is already embedded in it.  It's not yet clear
to me why it was invented, and whether it's a solution or a problem.  

--jkl