tree 4ee171b998ac695e441ec8cd1c975f7d08f22a65
parent 0817afa577428da457b6482c027d7202cd01fcbf
author Takuto Ikuta <tikuta@google.com> 1791453334 +0900
committer gn-scoped@luci-project-accounts.iam.gserviceaccount.com <gn-scoped@luci-project-accounts.iam.gserviceaccount.com> 1792065809 -0700

Stop forwarding private hard_deps on Rust targets

Previously, Rust targets (e.g. rust_library, rust_proc_macro) forwarded
hard_deps from both public_deps and private deps to their dependents
because Target::all_headers_public() defaults to true.

However, Rust targets do not have C/C++ public headers, and downstream
Rust targets already have direct dependencies on upstream .rlib/.rmeta
files. Private dependencies of a Rust target (such as Cargo build script
execution actions or internal rust_bindgen actions) are only needed to
compile the Rust target itself, while any generated C++ headers exposed
to dependents (e.g. cxxbridge or Crubit headers) are placed in
public_deps.

This change introduces ResolvedTargetData::OnlyForwardsPublicHardDeps()
and applies it to Rust targets in addition to check_includes_strict
targets, so that Rust targets only forward hard_deps from public_deps to
dependents while still including private hard_deps in their own
compilation input dependencies.

In a Chromium Linux build, this eliminates 377 .harddeps phony rules and
2,587 .harddeps dependency edges (including std.harddeps and 3p Cargo
crate build script outputs propagating into downstream C++ targets).

Bug: 563098656
Change-Id: If74076cba64281db575afea5b84f61c25f29bb09
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/27321
Reviewed-by: Matt Stark <msta@google.com>
Commit-Queue: Takuto Ikuta <tikuta@google.com>
Reviewed-by: David Turner <digit@google.com>