[PATCH] D39050: Add index-while-building support to Clang

[Marc-Andre Laperle via Phabricator via cfe-commits]

malaperle added a comment.

In https://reviews.llvm.org/D39050#948500, @akyrtzi wrote:

> @malaperle, to clarify we are not suggesting that you write your own parser, the suggestion is to use clang in 'fast-scan' mode to get the structure of the declarations of a single file, see `CXTranslationUnit_SingleFileParse` (along with enabling skipping of bodies). We have found clang is super fast when you only try to get the structure of a file like this.


Thank you, that sounds very useful. I will try that and get some measurements.

> We can make convenient APIs to provide the syntactic structure of declarations based on their location.

Perhaps just for the end-loc since it's pretty much guaranteed to be needed by everyone. But if it's very straightforward, perhaps that's not needed. I'll try and see.

> But let's say we added the end-loc, is it enough ? If you want to implement the 'peek the definition' like Eclipse, then it is not enough, you also need to figure out if there are documentation comments associated with the declaration and also show those. Also what if you want to highlight the type signature of a function, then just storing the location of the closing brace of its body is not enough. There can be any arbitrary things you may want to get from the structure of the declaration (e.g. the parameter ranges), but we could provide an API to gather any syntactic structure info you may want.

That's a very good point. I guess in the back of my mind, I have the worry that one cannot extend what is stored, either for a different performance trade-off or for additional things. The fact that both clang and clangd have to agree on the format so that index-while-building can be used seems to make it inherently not possible to extend. But perhaps it's better to not overthink this for now.


https://reviews.llvm.org/D39050