fix: support clang-cl #1045

K-ballo · 2025-10-01T09:16:54Z

fixes #904

continues the work from #997

src/lib/CorpusImpl.cpp

K-ballo · 2025-10-01T12:47:39Z

src/test/TestRunner.cpp

+        makeSingleFileDBForClang(filePath);
+#else
+        makeSingleFileDBForClangCL(filePath);
+#endif


this is still arbitrary.. there's no reason why both drivers couldn't be tested on every platform

furthermore, this triggers unused function warnings

this is still arbitrary

:)

would you suggest we run every test twice?
or should I rather conditionally define the one we're actually testing?

would you suggest we run every test twice?

Sure. All platforms must be able to read both file formats, so it makes sense to test both formats on all platforms.

I had to change the program name from "clang-cl" to just "cl", otherwise clang wasn't recognizing "/std:c++latest" on linux/macos. I do not have an explanation for this, why would it depend on the environment? @mizvekov ?

https://github.com/llvm/llvm-project/blob/4d32ea87673adaa5252545ca82fa6cd58b134ff9/clang/lib/Driver/ToolChain.cpp#L439

This didn't work out either. Is it possible to use CL mode on linux/macox? Does it require explicit --driver-mode?

@mizvekov Ideas?

cppalliance-bot · 2025-10-01T14:28:40Z

An automated preview of the documentation is available at https://1045.mrdocs.prtest2.cppalliance.org/index.html

src/lib/MrDocsCompilationDatabase.cpp

src/lib/CorpusImpl.cpp

src/test/lib/MrDocsCompilationDatabase.cpp

src/lib/MrDocsCompilationDatabase.cpp

src/test/TestRunner.cpp

cppalliance-bot · 2025-10-02T13:22:19Z

An automated preview of the documentation is available at https://1045.mrdocs.prtest2.cppalliance.org/index.html

cppalliance-bot · 2025-10-02T13:32:07Z

An automated preview of the documentation is available at https://1045.mrdocs.prtest2.cppalliance.org/index.html

cppalliance-bot · 2025-10-03T10:57:19Z

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2025-10-08 16:26:36 UTC

K-ballo · 2025-10-06T07:26:17Z

I just found out about clang-cl's /clang: option. Using it still requires conditionals, and it makes working with multiple token options difficult, but we could in principle do:

new_cmdline.emplace_back(is_clang_cl ? "/clang:-std=c++23" : "-std=c++23");
new_cmdline.emplace_back(is_clang_cl ? std::format("/clang:-isystem=\"{}\"", inc) : std::format("-isystem=\"{}\"", inc));

The benefit for these downsides is that mrdocs would not need to know about msvc flags. Thoughts?

alandefreitas · 2025-10-06T23:16:12Z

Thoughts?

That's a fantastic discovery!

In most cases, things would get much more readable because we would be expressing directly in code that we explicitly want both options in the ternary operator to represent the same thing.

We can even write a lambda or something that optionally wraps the flags with it, and the code would get much simpler.

Maybe @mizvekov knows of some drawbacks.

mizvekov · 2025-10-06T23:46:42Z

Oh yes I knew about the /clang: redirection flag, sorry that I didn't think to bring it up.

Using the redirection flag skips any driver specific behavior for that flag, the driver simply forwards it to another driver.

This could be, as one simple example, checking that one flag is compatible with another one.

I'd say this is best used for flags which don't have a specific counterpart in the cl driver.

I suppose it's not a big deal if we use it with a limited set of flags and use cases we have vetted are ok, but then this wouldn't be a big advantage versus simply not using it.

alandefreitas · 2025-10-07T01:15:15Z

Oh... OK. So it's best to reserve this for flags with no counterpart. Or maybe flags with no obvious counterpart, at least.

K-ballo · 2025-10-08T08:11:14Z

Everything should be in order now, but the PR is triggering some leaks deep within clang (while parsing libcxx headers).

@alandefreitas @mizvekov what's the procedure?

alandefreitas · 2025-10-08T15:53:16Z

@alandefreitas @mizvekov what's the procedure?

My procedure is to ask @mizvekov so you already did my procedure :)

mizvekov · 2025-10-08T16:06:23Z

@K-ballo

I'd try to preprocess and isolate it first.

These are probably clang bugs, I had to fix a few of these leaks in the past.

While clang is in general extensively tested with sanitizers, we run clang in a configuration which is not so tested, and there likely lies the problem.

K-ballo · 2025-10-08T16:13:10Z

I'd try to preprocess and isolate it first.

@mizvekov does that mean the clang-cl fix will be on hold until the clang leak is fixed upstream and mrdocs bumps its target llvm commit?

mizvekov · 2025-10-08T16:18:41Z

Yeah, but you could simply not commit the libc++ tests at this point, send that to a separate PR and lets fix it there.

The problem is pre-existing and only happens on new tests, so I don't see a problem. @alandefreitas ?

K-ballo · 2025-10-08T16:20:27Z

The problem is pre-existing and only happens on new tests,

The problem happens on existing tests, when run under a new configuration. So I take it the way to proceed is to leave clang-cl tests out on non-windows platforms.

mizvekov · 2025-10-08T16:23:44Z

The problem is pre-existing and only happens on new tests,

The problem happens on existing tests, when run under a new configuration. So I take it the way to proceed is to leave clang-cl tests out on non-windows platforms.

Yeah, that sounds fair to me, it would unblock this PR.

alandefreitas · 2025-10-08T16:35:04Z

while parsing libcxx headers

Is that in the new test, any of the old tests, or both?

If it's in any of the old tests or both, is it test-files/golden-tests/core/libcxx.cpp? I can't remember any other that would try to parse libcxx headers.

Also, under what conditions is this being triggered? Both CL and non-CL mode? All platforms? In this PR, the stubs haven't been replaced yet, and although we use a different driver, it's always clang under the hood. So the problem was already there, right?

Is any sanitizer catching this? Depending on the case, we may need to reevaluate whether we want sanitizers in dependencies when they are not a strict requirement. The ROI is very low (for the ones with false negatives only: ASan and UBSan) so we'll have to remove them from dependencies if they keep getting bugs we can't fix. Especially after #1030, when we won't be able to control the environment as much.

alandefreitas · 2025-10-08T16:44:45Z

so I don't see a problem. @alandefreitas ?

In general, I agree with the "feeling", so to speak. But at the same time, unblocking PRs is not our end goal in itself. We need to have clarity about the conditions under which we're seeing the bug, including which tests it appears in, what came before the PR, what's causing it, and how complex it would be to fix. With this information, we can make an informed decision on what's more beneficial to the project. It could be just fixing it or opening an independent issue that "unblocks" the PR.

K-ballo · 2025-10-08T17:23:50Z

Also, under what conditions is this being triggered?

Clang 21: C++20 (ASan) is reporting a leak deep within clang when testing test-files/golden-tests/core/libcxx.cpp in CL mode (requires specifying a windows-msvc target)

we may need to reevaluate whether we want sanitizers in dependencies when they are not a strict requirement.

There should be a procedure on how to deal with sanitizer failures in dependencies. I'm not saying they should be ignored, I don't think it's reasonable to hold important fixes.

alandefreitas · 2025-10-08T17:30:55Z

procedure on how to deal with sanitizer failures in dependencies

Exactly. That's why I made all those questions. The details matter here.

CI will not be able to determine where the problem originates.

@mizvekov Isn't ASan supposed to be making CI fail, by the way?

alandefreitas · 2025-10-08T17:32:24Z

Isn't ASan supposed to be making CI fail, by the way?

Doesn't Asan in clang include LSan? Or is it disabled for some reason? Or if it doesn't, maybe that's why the GCC PR is failing?

mizvekov · 2025-10-08T17:35:02Z

It is failing, I believe this PR is only passing because @K-ballo just disabled the libcxx tests here, in other to confirm the problem.

alandefreitas · 2025-10-08T17:40:11Z

Clang 21: C++20 (ASan) is reporting a leak deep within clang when testing test-files/golden-tests/core/libcxx.cpp in CL mode (requires specifying a windows-msvc target)

What does "requires specifying a windows-msvc target" mean in the context of this PR? Only that the compilation database we give clang uses CL syntax?

K-ballo · 2025-10-08T17:56:01Z

What does "requires specifying a windows-msvc target" mean in the context of this PR?

passing "-target x86_64-pc-windows-msvc" (or similar) to clang-cl

alandefreitas · 2025-10-08T18:38:01Z

passing "-target x86_64-pc-windows-msvc" (or similar) to clang-cl

Ooooooooh. OK. I get it now.

You're not passing it via (not "to") the cl driver syntax (not to "clang-cl", which is a program), but
the driver implicitly includes -target x86_64-pc-windows-msvc anyway when generating the commands for the frontend, and
this leads to a difference in the final commands that
probably lead to different conditions in the headers and
then leads to an error

OK. Since this is not ultimately compiled to any target anyway (clang is just parsing the code), the problem is related to some MACRO being defined at this lower level.

Yes. It makes sense to fix the issue then. It's not an unrelated blocker, but the logic most Windows users will be using. Or at least not ignoring the issue completely and moving on without caring about what's happening.

One thing you might want to play with is disabling the libcxx stubs option for this text case, although I'm not sure tests look for the implicit compiler include paths to replace the stubs (the other issue will have to do it sooner or later because it's a requirement for some tests).

K-ballo · 2025-10-09T06:47:35Z

Yes. It makes sense to fix the issue then.

It always makes sense to fix the issue. The question here is whether the clang-fix should be blocked by the clang leak fix.

K-ballo commented Oct 1, 2025

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K-ballo requested review from alandefreitas and mizvekov October 1, 2025 14:18

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alandefreitas mentioned this pull request Oct 1, 2025

fix(ci): setup C++ when building releases #1041

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K-ballo force-pushed the clang-cl branch from 9fb38e5 to 7e1d474 Compare October 2, 2025 13:25

K-ballo mentioned this pull request Oct 3, 2025

target latest clang supported standard if -std not given #1047

Open

K-ballo force-pushed the clang-cl branch 2 times, most recently from c546c2f to c2b61ad Compare October 6, 2025 07:07

K-ballo added 3 commits October 8, 2025 18:21

Run tests using clang-cl on windows

8fecaec

Use clang-cl system includes syntax

ceae5cf

Use clang-cl nostdlibinc option

80f0642

K-ballo added 18 commits October 8, 2025 18:21

tweaks

80e7bc1

salvage some tests...

2346709

test -std

5f99dee

test defines

bf236a3

test systemIncludes

5d33325

flip

cb7e466

unused

0fd8d7e

default

50c3257

test std more

925940c

separate cases

3cd0506

decide flag spelling once

0b2fd91

isClangCL

f3921c3

silence warning

8622344

test both clang and clang-cl modes

ede7fee

uh?

359687d

fix clang-cl default std flags

98c07f4

adjust -std: test

9d7cca7

adjust more

996899a

K-ballo force-pushed the clang-cl branch from 97b9798 to 996899a Compare October 8, 2025 16:22

fix: support clang-cl #1045

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fix: support clang-cl #1045

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