Generate ccache wrapper scripts instead of symlink

[chenhao94]

Tested with Bazel 5.2. It is a workaround for issue
bazelbuild/rules_cc#130

[xkszltl]

• What's the bug previously?
• Is it fixed in upstream?
• If it's symlink-related, can we use the same CC approach with scripts instead of symlink?
• Put some comments in place about what's working and what's not.

[chenhao94]

• What's the bug previously?

ccache symlink to clang will be derefed by Bazel

• Is it fixed in upstream?

No.

• If it's symlink-related, can we use the same CC approach with scripts instead of symlink?

That is exactly what this PR does.

• Put some comments in place about what's working and what's not.

Will do

[xkszltl]

That is exactly what this PR does.

I mean give it CC without PATH

[chenhao94]

That is exactly what this PR does.

I mean give it CC without PATH

No, because Bazel does not like full path. I # think the point is, you either use installed compilers (those can be find by which), or define a Bazel toolchain. The latter one seems to be a preferred way.

[xkszltl]

... or define a Bazel toolchain. The latter one seems to be a preferred way.

Not sure what does toolchain looks like here, but it should still use the full path.
Problem with PATH is you're not suppose to expose this to whatever Bazel's calling.
They may not like to PATH required by PATH.
PATH is used by everything, but things like CC has a much narrower context.

[chenhao94]

... or define a Bazel toolchain. The latter one seems to be a preferred way.

Not sure what does toolchain looks like here, but it should still use the full path.
Problem with PATH is you're not suppose to expose this to whatever Bazel's calling.
They may not like to PATH required by PATH.
PATH is used by everything, but things like CC has a much narrower context.

The customized toolchain does need full paths. The auto generated toolchain is also using the full paths, but the default auto toolchain generator does not like full paths in CC for whatever reason.

In this particular case, we set the PATH variable only for bazel build command, and we know there are only our ccache wrappers in that added PATH.