Header inclusion checking in src/hdrs for cc_library is broken

[nathaniel-brough]

Description of the bug:

Header inclusion checking seems to be broken. In the documentation for cc_library, it mentions that adding header files to the srcs attribute should make them private to dependent targets. However, this is not the case.

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Create a skeleton repository based on the example in the Bazel documentation;

cc_binary(
    name = "foo",
    srcs = [
        "foo.cc",
        "foo.h",
    ],
    deps = [":bar"],
)

cc_library(
    name = "bar",
    srcs = [
        "bar.cc",
        "bar-impl.h",
    ],
    hdrs = ["bar.h"],
    deps = [":baz"],
)

cc_library(
    name = "baz",
    srcs = [
        "baz.cc",
        "baz-impl.h",
    ],
    hdrs = ["baz.h"],
)

Try and include bar-impl.h from foo.cc. According to the documentation, this should produce an error, however, it does not and instead builds successfully.

Including file	Allowed inclusions
foo.h	bar.h
foo.cc	foo.h bar.h
bar.h	bar-impl.h baz.h
bar-impl.h	bar.h baz.h
bar.cc	bar.h bar-impl.h baz.h
baz.h	baz-impl.h
baz-impl.h	baz.h
baz.cc	baz.h baz-impl.h

Which operating system are you running Bazel on?

Ubuntu 20.04 (WSL)

What is the output of bazel info release?

5.4.0

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

#14346
#7030
#3828

Any other information, logs, or outputs that you want to share?

No response

[fmeum]

If you include bar-impl.h from foo.cc, use clang and enable the layering_check feature, you get this error:

bazel build //:foo --repo_env=CC=clang --features=layering_check
foo.cc:3:10: error: use of private header from outside its module: 'bar-impl.h' [-Wprivate-header]
#include "bar-impl.h"
         ^
1 error generated.

This works even better then the docs mention. While they say "For example, Bazel would not complain if in the example above foo.cc directly includes baz.h.", if you try that, you get this error:

bazel build //:foo --repo_env=CC=clang --features=layering_check
foo.cc:3:10: error: module //:foo does not depend on a module exporting 'baz.h'
#include "baz.h"
         ^
1 error generated.

[nathaniel-brough]

Hmm, so in the example, you gave above, it's pretty clear that this feature is working (with the layering check feature enabled). Perhaps, it's just a documentation error and the docs should just mention the layering_check feature?

[fmeum]

I submitted #17057 to improve the documentation of this feature.