Fix rebuild issues with rustdoc.

src/cargo/core/compiler/context/compilation_files.rs

@@ -598,7 +598,7 @@ fn hash_rustc_version(bcx: &BuildContext<'_, '_>, hasher: &mut StableHasher) {
 
 /// Returns whether or not this unit should use a metadata hash.
 fn should_use_metadata(bcx: &BuildContext<'_, '_>, unit: &Unit) -> bool {
-    if unit.mode.is_doc_test() {
+    if unit.mode.is_doc_test() || unit.mode.is_doc() {
         // Doc tests do not have metadata.
         return false;
     }

src/cargo/core/compiler/mod.rs

@@ -594,7 +594,8 @@ fn rustdoc(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Work> {
     // script_metadata is not needed here, it is only for tests.
     let mut rustdoc = cx.compilation.rustdoc_process(unit, None)?;
     rustdoc.inherit_jobserver(&cx.jobserver);
-    rustdoc.arg("--crate-name").arg(&unit.target.crate_name());
+    let crate_name = unit.target.crate_name();
+    rustdoc.arg("--crate-name").arg(&crate_name);
     add_path_args(bcx.ws, unit, &mut rustdoc);
     add_cap_lints(bcx, unit, &mut rustdoc);
 
@@ -608,7 +609,7 @@ fn rustdoc(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Work> {
     // it doesn't already exist.
     paths::create_dir_all(&doc_dir)?;
 
-    rustdoc.arg("-o").arg(doc_dir);
+    rustdoc.arg("-o").arg(&doc_dir);
 
     for feat in &unit.features {
         rustdoc.arg("--cfg").arg(&format!("feature=\"{}\"", feat));
@@ -648,6 +649,13 @@ fn rustdoc(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Work> {
                 }
             }
         }
+        let crate_dir = doc_dir.join(&crate_name);
+        if crate_dir.exists() {
+            // Remove output from a previous build. This ensures that stale
+            // files for removed items are removed.
+            log::debug!("removing pre-existing doc directory {:?}", crate_dir);
+            paths::remove_dir_all(crate_dir)?;
+        }
         state.running(&rustdoc);
 
         rustdoc

tests/testsuite/doc.rs

@@ -863,10 +863,44 @@ fn features() {
             r#"#[cfg(feature = "bar")] pub fn bar() {}"#,
         )
         .build();
-    p.cargo("doc --features foo").run();
+    p.cargo("doc --features foo")
+        .with_stderr(
+            "\
+[COMPILING] bar v0.0.1 [..]
+[DOCUMENTING] bar v0.0.1 [..]
+[DOCUMENTING] foo v0.0.1 [..]
+[FINISHED] [..]
+",
+        )
+        .run();
     assert!(p.root().join("target/doc").is_dir());
     assert!(p.root().join("target/doc/foo/fn.foo.html").is_file());
     assert!(p.root().join("target/doc/bar/fn.bar.html").is_file());
+    // Check that turning the feature off will remove the files.
+    p.cargo("doc")
+        .with_stderr(
+            "\
+[COMPILING] bar v0.0.1 [..]
+[DOCUMENTING] bar v0.0.1 [..]
+[DOCUMENTING] foo v0.0.1 [..]
+[FINISHED] [..]
+",
+        )
+        .run();
+    assert!(!p.root().join("target/doc/foo/fn.foo.html").is_file());
+    assert!(!p.root().join("target/doc/bar/fn.bar.html").is_file());
+    // And switching back will rebuild and bring them back.
+    p.cargo("doc --features foo")
+        .with_stderr(
+            "\
+[DOCUMENTING] bar v0.0.1 [..]
+[DOCUMENTING] foo v0.0.1 [..]
+[FINISHED] [..]
+",
+        )
+        .run();
+    assert!(p.root().join("target/doc/foo/fn.foo.html").is_file());
+    assert!(p.root().join("target/doc/bar/fn.bar.html").is_file());
 }
 
 #[cargo_test]