[PATCH] D147905: [clangd] Avoid passing -xobjective-c++-header to the system include extractor

[Kadir Cetinkaya via Phabricator via cfe-commits]

kadircet added inline comments.


================
Comment at: clang-tools-extra/clangd/SystemIncludeExtractor.cpp:340
+    // is not installed.
+    if (Lang == "objective-c++-header") {
+      Lang = "c++-header";
----------------
nridge wrote:
> kadircet wrote:
> > this feels like too much of a layering violation and might (will?) go wrong in cases where language was explicitly set to `objective-c++-header`.
> > 
> > if the user is relying on fallback commands with an overwrite of `Compiler:` in the config && --query-driver globs, would it be too much of a hassle to expect them to have a `CompileFlags: Add: ...` block too?
> > this feels like too much of a layering violation and might (will?) go wrong in cases where language was explicitly set to `objective-c++-header`.
> 
> This has occurred to me, and my first idea for a fix was to limit this change to cases where the `-xobjective-c++-header` originates from the fallback command.
> 
> However, as mentioned [here](https://github.com/clangd/clangd/issues/1568#issuecomment-1493236437), when I tested this I found that `-xobjective-c++-header` did not make any difference (compared to `-xc++-header` or  `-xc++`) in the include paths returned by gcc. In other words, in gcc's include directory structure there are no objc-specific directories. This made me think this simpler fix would be appropriate.
> 
> > if the user is relying on fallback commands with an overwrite of `Compiler:` in the config && --query-driver globs, would it be too much of a hassle to expect them to have a `CompileFlags: Add: ...` block too?
> 
> You're right, adding a section like this to the config does seem to be a viable workaround:
> 
> ```
> ---
> 
> If:
>   PathMatch: *\.h
> 
> CompileFlags:
>   Add: [-xc++-header]
> ```
> 
> But I think it would still be nice to fix this in clangd, as being foiled by objective-c support not being installed is a very unexpected failure mode for a user whose project does not involve objective-c at all.
> 
> For what it's worth, I don't think this kind of setup is uncommon. A common scenario seems to be a casual user playing around with a small project (hence, doesn't have a build system or compile_commands.json), on a platform where --query-driver is needed to find the standard library headers (most commonly, MinGW on Windows).
> However, as mentioned [here](https://github.com/clangd/clangd/issues/1568#issuecomment-1493236437), when I tested this I found that `-xobjective-c++-header` did not make any difference (compared to `-xc++-header` or  `-xc++`) in the include paths returned by gcc. In other words, in gcc's include directory structure there are no objc-specific directories.

Well, that's definitely re-assuring, but I am not sure if it's enough to say it'll work that way with all gcc's or when there are other/certain "system" libraries installed. As in theory objc compilation should at least add some framework search paths and what not by default, no?

> But I think it would still be nice to fix this in clangd, as being foiled by objective-c support not being installed is a very unexpected failure mode for a user whose project does not involve objective-c at all.

Completely agree, but we're only showing that to people that already fiddled with clangd internals. So I don't think that as  unacceptable.
 
> For what it's worth, I don't think this kind of setup is uncommon. A common scenario seems to be a casual user playing around with a small project (hence, doesn't have a build system or compile_commands.json), on a platform where --query-driver is needed to find the standard library headers (most commonly, MinGW on Windows).

I think instead of trying to make things work with query-driver in such setups, we should try to make sure things work out-of-the-box in mingw (and other toolchain) setups. I believe people not using query-driver in such vanilla installation is way more common than people using query-driver and `CompileFlags.Compiler` override. Also this will probably make sure other clang-tools can work with those setups too.
We have mingw toolchain detection [here](https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/MinGW.cpp).


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D147905/new/

https://reviews.llvm.org/D147905