[cdt-dev] What use cases does PDOMDependencyCalculator solve?

[Raphael Zulliger <zulliger@xxxxxxxx>]

In a customers project, they encounter intolerable long times between 
"project build" invocation and the execution start of "make" which takes 
more than minutes on some (Windows) systems. This time is consumed 
during "build configuration" creation. A considerable amount of time is 
spent in findTypeForExtension called by BuildDescription.completeLinking.

What massively speeds up things (actually fixes the issue) is to avoid 
PDOMDependencyCalculator being used (e.g. by disabling indexer or by 
patching the code accordingly). Right now, I'm thinking about patching 
CDT for our customers to disable PDOMDependencyCalculator - but first 
I'd like to understood what the purpose of that class acutally is, 
means: what "real life problem" it solves. While it's obvious that it 
adds all dependencies (i.e. included headers) to a certain .cpp, it's 
not obvious to me why this is required for CDT to know. Don't we use 
make and .d files to generate and handle such dependencies? (note: I'm 
aware of https://bugs.eclipse.org/bugs/show_bug.cgi?id=108715, which 
discusses some possible make pitfalls - but I think those are not 
related to this issue, are they?)

Thanks,
Raphael