fix(doc): respect public-dependency when documenting deps

Author: ojuschugh1

src/cargo/core/compiler/unit_dependencies.rs

@@ -67,6 +67,12 @@ struct State<'a, 'gctx> {
     /// dependency from a to b was added purely because it was a dev-dependency.
     /// This is used during `connect_run_custom_build_deps`.
     dev_dependency_edges: HashSet<(Unit, Unit)>,
+
+    /// The set of packages explicitly selected by the user (e.g. via `-p`).
+    /// Used to determine whether to apply the public-dependency doc filter:
+    /// only root packages bypass the filter; their deps must be public to
+    /// have their own docs generated.
+    root_pkg_ids: HashSet<PackageId>,
 }
 
 /// A boolean-like to indicate if a `Unit` is an artifact or not.
@@ -126,6 +132,7 @@ pub fn build_unit_dependencies<'a, 'gctx>(
         interner,
         scrape_units,
         dev_dependency_edges: HashSet::new(),
+        root_pkg_ids: roots.iter().map(|u| u.pkg.package_id()).collect(),
     };
 
     let std_unit_deps = calc_deps_of_std(&mut state, std_roots)?;
@@ -637,6 +644,21 @@ fn compute_deps_doc(
     // built. If we're documenting *all* libraries, then we also depend on
     // the documentation of the library being built.
     let mut ret = Vec::new();
+
+    // Check if public-dependency feature is enabled
+    let public_deps_enabled = state.gctx.cli_unstable().public_dependency
+        || unit
+            .pkg
+            .manifest()
+            .unstable_features()
+            .is_enabled(Feature::public_dependency());
+
+    // Whether this package was explicitly selected by the user (e.g. via `-p`).
+    // User-selected packages always have all their direct deps documented,
+    // regardless of public/private status. For everything else, only public
+    // deps get their own docs generated when public-dependency is enabled.
+    let is_user_selected = state.root_pkg_ids.contains(&unit.pkg.package_id());
+
     for (id, deps) in state.deps(unit, unit_for) {
         let Some(dep_lib) = calc_artifact_deps(unit, unit_for, id, &deps, state, &mut ret)? else {
             continue;
@@ -657,7 +679,20 @@ fn compute_deps_doc(
             IS_NO_ARTIFACT_DEP,
         )?;
         ret.push(lib_unit_dep);
-        if dep_lib.documented() && state.intent.wants_deps_docs() {
+
+        // Decide whether to document this dependency.
+        // When public-dependency is enabled, only document:
+        // - Direct dependencies of user-selected packages
+        // - Public dependencies (recursively)
+        // This dramatically speeds up documentation builds by excluding indirect
+        // private dependencies that cannot be used by readers of the docs.
+        let should_doc_dep = if is_user_selected || !public_deps_enabled {
+            true
+        } else {
+            state.resolve().is_public_dep(unit.pkg.package_id(), id)
+        };
+
+        if dep_lib.documented() && state.intent.wants_deps_docs() && should_doc_dep {
             // Document this lib as well.
             let doc_unit_dep = new_unit_dep(
                 state,

tests/testsuite/doc.rs

@@ -4218,7 +4218,6 @@ fn doc_with_private_dependency() {
 [DOWNLOADING] crates ...
 [DOWNLOADED] baz v0.0.1 (registry `dummy-registry`)
 [DOWNLOADED] bar v0.0.1 (registry `dummy-registry`)
-[DOCUMENTING] baz v0.0.1
 [CHECKING] baz v0.0.1
 [DOCUMENTING] bar v0.0.1
 [CHECKING] bar v0.0.1
@@ -4233,7 +4232,7 @@ fn doc_with_private_dependency() {
 
     assert!(p.root().join("target/doc/foo/index.html").is_file());
     assert!(p.root().join("target/doc/bar/index.html").is_file());
-    assert!(p.root().join("target/doc/baz/index.html").is_file());
+    assert!(!p.root().join("target/doc/baz/index.html").is_file());
 }
 
 #[cargo_test(nightly, reason = "public-dependency feature is unstable")]
@@ -4290,17 +4289,21 @@ fn doc_mixed_public_private_deps() {
             .join("target/doc/priv_dep_with_dep/index.html")
             .is_file()
     );
-    assert!(p.root().join("target/doc/transitive/index.html").is_file());
+    assert!(!p.root().join("target/doc/transitive/index.html").is_file());
 }
 
 #[cargo_test(nightly, reason = "public-dependency feature is unstable")]
 fn doc_workspace_member_private_dep() {
     // selected and skipped are both workspace members.
     // selected has a private dep on skipped.
     // skipped has a dep on transitive (a registry crate).
-    // Running `cargo doc -p selected` currently documents all of them,
-    // including transitive, because the public-dependency filter is not
-    // applied to workspace members' deps.
+    // Running `cargo doc -p selected`:
+    // - selected is documented (it is user-selected)
+    // - skipped is documented because it is a direct dep of selected (user-selected
+    //   packages always have all their direct deps documented)
+    // - transitive is NOT documented: skipped is not user-selected, so the
+    //   public-dependency filter applies to its deps, and transitive is not
+    //   marked public by skipped
 
     Package::new("transitive", "0.0.1")
         .file("src/lib.rs", "pub fn transitive() {}")
@@ -4348,8 +4351,11 @@ fn doc_workspace_member_private_dep() {
         .masquerade_as_nightly_cargo(&["public-dependency"])
         .run();
 
+    // selected is documented (user-selected)
     assert!(p.root().join("target/doc/selected/index.html").is_file());
+    // skipped is documented because it is a direct dep of the user-selected package
     assert!(p.root().join("target/doc/skipped/index.html").is_file());
-    // transitive is documented under the current behavior (no filter applied)
-    assert!(p.root().join("target/doc/transitive/index.html").is_file());
+    // transitive is NOT documented: skipped is not user-selected, and it does
+    // not mark transitive as public
+    assert!(!p.root().join("target/doc/transitive/index.html").is_file());
 }