[Bazel] @llvm-project//llvm:Support fails to build due to incomplete DelimitedScope

[hankhsu1996]

When using @llvm-project//llvm:Support as a dependency in a Bazel-based C++ project, the build fails even before any actual LLVM headers are included. This happens because Bazel eagerly compiles all sources listed in the Support target.

In this case, ScopedPrinter.cpp includes ScopedPrinter.h, which forward-declares DelimitedScope but never defines it. This leads to the following compile error from the standard library:

error: invalid application of 'sizeof' to an incomplete type 'llvm::DelimitedScope'

My project uses Bazel modules and depends on LLVM like this:

bazel_dep(name = "llvm-project", version = "17.0.3.bcr.2")

And in my cc_library:

deps = ["@llvm-project//llvm:Support"]

Even without writing any code that includes LLVM headers, Bazel tries to compile all of Support’s sources and fails due to this issue.

Suggested fix: define DelimitedScope or remove ScopedPrinter.cpp from the Support target until it's complete.

[hankhsu1996]

This issue is not caused by LLVM upstream. It turns out the problem only exists in the LLVM Bazel module version 17.0.3.bcr.2 used via BCR. The current LLVM codebase has already fixed this issue.