From https://crrev.com/c/1160648/3/third_party/blink/public/common/BUILD.gn#97 ...

In that CL, drott@ wants to change things so that if a target depends on //third_party/blink/public/common, they have to depend on //third_party/blink/public/common:font_unique_name_table_proto, so that a user of public/common (like //content/browser) doesn't need to directly depend on it.

So, for convenience we'll label these as A, B, and C:

//content/browser (A) ->
  //third_party/blink/public/common (B) ->
    //third_party/blink/public/common:font_unique_name_table_proto (C)

This looks like a case for public_deps, i.e., B would simply declare C as a public_dep, not a dep.

However, in  the desired build config, B is a shared_library (component), and C is a static_library, and it looks like things are implemented such that static_libraries do *not* propagate across the shared_library boundary, and so if you try to link A, you'll get linker errors from the missing C (whereas in a static build, I think this would work fine).

I believe this is by design, because it reduces the possibility for multiple linkage (C getting linked into both A and B, potentially violating ODR rules), and, in general, multiple linkage like this would be bad.

I think there are two workarounds for this. The first is for A to explicitly declare the dependency on C, which is in fact what the original CL did. The second is to change things so that C is a component, not a static library, since shared_library deps *do* propagate across, since they won't be multiply-linked. I suspect the second is probably preferable, since it would reduce multiple linkage and produce similar behavior across shared and static builds.

My questions for brettw@ are:

(1) Does this all sound correct?

(2) Do you think it might make sense for us to have some sort of flag to indicate that a static_library (or a source_set) can be safely multiply-linked and should propagate across?

My guess is that the answer is, no, it's probably to accidentally make something stop being multiple-link-safe, but I thought I'd double-check.

If your answers are "yes" and "no", respectively, then I think it's safe to close this as WontFix, unless we're both missing something, in which case drott@ can hopefully speak up :).