[PATCH] D154903: clangd: Provide the resource dir via environment variable

[Sam McCall via Phabricator via cfe-commits]

sammccall added a comment.

I'm a little nervous about this. On the one hand it's simple and I want to get you unblocked but:

- the more ways to initialize resource dir and the more places this needs to be propagated to, the more likely this is to get out of sync
- we might want to remove the need for resource-dir one day and embed the built-in-headers in the binary, it's not clear what this would do in such a world.
- I don't understand how the technique this enables can be robust. Using the built-in headers from one compiler with a different compiler may work sometimes but is going to break in mysterious ways. I don't want to stop you using this technique, but if we add a feature for this people will want support in using it correctly.

It seems like you can *almost* do this with no new support though - the driver will always be invoked by clangd, so you can ask the OS where the invoking binary is. This assumes:

- you're on an OS where this is reasonably possible
- you're not customizing the resource-dir path, so we can use the same heuristics clangd does to find it

Proof of concept (works on my machine!) to access the resource dir from the driver - this just sets it as an include path but you could do whatever:

  #!/bin/bash
  # /home/sammccall/qd/driver.sh
  echo "Target: x86_64-linux-gnu" >&2
  echo "#include \"...\" search starts here:" >&2
  echo "#include <...> search starts here:" >&2
  echo $(dirname $(dirname $(readlink /proc/$PPID/exe)))/lib/clang/*/include >&2
  echo "End of search list." >&2

  # /home/sammccall/qd/.clangd
  CompileFlags:
    Compiler: /home/sammccall/qd/driver.sh

  $ env CLANGD_FLAGS=--query-driver="/home/sammccall/qd/driver.sh" clangd --check=/home/sammccall/qd/hello.cc -log=verbose
  ...
  I[10:09:51.174] Failed to find compilation database for /home/sammccall/qd/hello.cc
  V[10:09:51.177] System include extraction: target extracted: "x86_64-linux-gnu"
  V[10:09:51.177] System include extraction: adding /usr/lib/clangd/lib/clang/16/include
  I[10:09:51.177] System includes extractor: successfully executed /home/sammccall/qd/driver.sh
  	got includes: "/usr/lib/clangd/lib/clang/16/include"
  	got target: "x86_64-linux-gnu"
  I[10:09:51.177] Generic fallback command is: [/home/sammccall/qd] /home/sammccall/qd/driver.sh -isystem /usr/lib/clangd/lib/clang/16/include --target=x86_64-linux-gnu -resource-dir=/usr/lib/clangd/lib/clang/16 -- /home/sammccall/qd/hello.cc
  ...

If this doesn't seem workable, can you explain a bit more about your setup?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D154903/new/

https://reviews.llvm.org/D154903