[PATCH] D54872: [clangd] Add ability to not use -resource-dir at all

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov added a comment.

In D54872#1309075 <https://reviews.llvm.org/D54872#1309075>, @malaperle wrote:

> In D54872#1307775 <https://reviews.llvm.org/D54872#1307775>, @ilya-biryukov wrote:
>
> > We have to point clangd into the resource dir, corresponding to the version of the headers it was built with. It's important we pick the exact version of the built-in headers that clangd was built for.
>
>
> Can you clarity/confirm "headers it was built with"?


There are two categories of headers we care about:

- the built-in headers that correspond to the `clang-headers` build target (they typically live in `./lib/clang/<version>/` if clang lives in `./bin`). These headers should be provided alongside the clang-based tools, it's not ok to use the ones from a different version of the compiler (one might get spurious compiler errors or even crashes). We inject `-resource-dir` in clangd to make sure we pick up the version of built-in headers that we ship.
- the C and C++ library headers, e.g. `<vector>`, `<stdio.h>`, etc. Those are not tied to the compiler version, so we just pick up the one based on the compilation database.

>   For example, if I build Clangd using Xcode's Clang, then running this Clangd, I would have to point to Xcode's Clang headers? 

In this example we should point the `-resource-dir` to pick up the headers from the `clangd` distribution, **not** XCode headers.

> This is what I have observed when using Clangd on Clangd's code. What if I compile Clangd with another non-Clang compiler?

Users shouldn't point `-resource-dir` into XCode's headers, this might break if the versions are sufficiently different.  D54630 <https://reviews.llvm.org/D54630> should fix this, it's under review.

> The problematic case is a bit different than I originally thought. The CDB contains an include path to the built-in headers of the Clang (windows installer) used to build the project, let's call the compiler Clang1. I also built Clang+Clangd separately from this Clang1, using CL, let's call it Clang2. When running that custom Clangd, the fallback resource-dir is the one from Clang2. I haven't looked deeply to confirm this, but having an include path to Clang1 (windows installer) and resource-dir to Clang2 (custom build) seems like would likely not work. In fact, when running Clangd from Clang2 and setting resource-dir to Clang1, it works properly. Now, I don't know if it's the CDB that's wrongly including the headers of Clang1 or if the CDB should include -resource-dir to Clang1. In any case, I'll spend a bit more time clarifying this.

What is the actual error you're getting? It would be nice to have a repro, so that we can look into the details of the issue. I suspect this might be similar to the issues we're running into on Mac (see D54630 <https://reviews.llvm.org/D54630> for details), where the `-resource-dir` is used to find the C++ STL headers in addition to the built-in headers.


Repository:
  rCTE Clang Tools Extra

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