Inject compiler_builtins during postprocessing and ensure it is made private

[tgross35]

Follow up of #135278

Do the following:

• Inject compiler_builtins during postprocessing, rather than injecting extern crate compiler_builtins as _ into the AST
• Do not make dependencies of std private by default (this was added in Exclude dependencies of std for diagnostics #135278)
• Make sure sysroot crates correctly mark their dependencies private/public
• Ensure that marking a dependency private makes its dependents private by default as well, unless otherwise specified
• Do the compiler_builtins update that has been blocked on this

There is more detail in the commit messages. This includes the changes I was working on in #136226.

try-job: test-various
try-job: x86_64-msvc-1
try-job: x86_64-msvc-2
try-job: i686-mingw-1
try-job: i686-mingw-2

r? @bjorn3

[tgross35]

The test still fails, and I cannot chase down how gimli is getting into the sysroot as non-private. Locally I am testing with submodules updated too.

r? bjorn3

[bjorn3]

Maybe you can make the code that checks if a crate is private for diagnostics check if all paths to reach a dependency are private and if so consider the dependency to be private even if the direct dependent crate doesn't mark it as private?

[tgross35]

Do you mean to do that as part of the is_private_dep check?

I am apparently missing some path since exposing more traits in builtins seems to leak into diagnostics still #135560. Haven't looked into it yet, but I suppose that might fix it.

[bjorn3]

Do you mean to do that as part of the is_private_dep check?

Yes

[tgross35]

It looks like the reason compiler_builtins is not showing up as private is because it shows up as an extern crate item with a no-location span, which gets picked up at

rust/compiler/rustc_resolve/src/build_reduced_graph.rs

Line 1321 in 77a4553

self.build_reduced_graph_for_item(item);

. I'm still trying to figure out where this would come from.

[tgross35]

This looks like a possibility

rust/compiler/rustc_builtin_macros/src/standard_library_imports.rs

Lines 49 to 61 in 77a4553

	let item = if name == sym::compiler_builtins {
	// compiler_builtins is a private implementation detail. We only
	// need to insert it into the crate graph for linking and should not
	// expose any of its public API.
	//
	// FIXME(#113634) We should inject this during post-processing like
	// we do for the panic runtime, profiler runtime, etc.
	cx.item(
	span,
	Ident::new(kw::Underscore, ident_span),
	thin_vec![],
	ast::ItemKind::ExternCrate(Some(name)),
	)

[tgross35]

@bors try

[tgross35]

I kept that in case a retest with further changes was needed. Dropped it now and squashed the last fixup.

[bjorn3]

@bors r+

[bors]

📌 Commit 9392580 has been approved by bjorn3

It is now in the queue for this repository.