Build a common index using clangd and serve it?

[rovere]

Dear all,
I guess many of us are using editors that, one way or another, are using LSP and clangd to make our coding within CMSSW a more pleasant experience.
Since the introduction of the "compilation commands" via compile_commands.json, our life (mine for sure) became much easier, because we know how to correctly parse our repository.
I was wondering if it could be feasible/useful to have the outcome of the parsing saved somewhere and served to the whole CMS/CMSSW community.

[cmsbuild]

cms-bot internal usage

[cmsbuild]

A new Issue was created by @rovere.

@Dr15Jones, @antoniovilela, @makortel, @mandrenguyen, @rappoccio, @sextonkennedy, @smuzaffar can you please review it and eventually sign/assign? Thanks.

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[makortel]

assign core

[cmsbuild]

New categories assigned: core

@Dr15Jones,@makortel,@smuzaffar you have been requested to review this Pull request/Issue and eventually sign? Thanks

[smuzaffar]

@iarspider , can you please look in to this?

[iarspider]

There are, in theory, two methods of using shared index:

The simple one

• Generate index using clangd-indexer (is not installed automatically so we need to update llvm recipe or use prebuilt executable). Building an index takes about 40 minutes, parallelizes automatically. Not incremental.
• Push it to cvmfs (single file, ~250 Mb)
• Download it when running scram project (optional)
• Tell clangd where to look for prebuilt index:

$ cat .clangd
    Index:
      External:
        File: /path/to/clangd.dex
      Background: Skip

* Path can be relative to `.clangd` location

• Can use clangd provided by the OS

There is, supposedly, no way to map local paths to build paths when using local index - but there is a way when using clangd-index-server. link

The hard one

• Generate index using clangd-indexer
• Serve it using clangd-index-server
  • Requires building llvm with remote capabilities, which add dependency on gRPC and protobuf.
• Users will need to use clangd with remote capabilities (os-provided one usually does not have remote capabilities)
• Tell clangd how to connect to index server:

$ cat .clangd
    Index:
      External:
        Server: my.index.server.com:50051

• Need one server per index (i.e. per release series)