fix(rustdoc-map): dedup --extern-html-too-url for same unit

src/cargo/core/compiler/rustdoc.rs

@@ -7,6 +7,7 @@ use crate::sources::CRATES_IO_REGISTRY;
 use crate::util::errors::{internal, CargoResult};
 use cargo_util::ProcessBuilder;
 use std::collections::HashMap;
+use std::collections::HashSet;
 use std::fmt;
 use std::hash;
 use url::Url;
@@ -113,8 +114,12 @@ fn build_all_urls(
     name2url: &HashMap<&String, Url>,
     map: &RustdocExternMap,
     unstable_opts: &mut bool,
+    seen: &mut HashSet<Unit>,
 ) {
     for dep in build_runner.unit_deps(unit) {
+        if !seen.insert(dep.unit.clone()) {
+            continue;
+        }
         if !dep.unit.target.is_linkable() || dep.unit.mode.is_doc() {
             continue;
         }
@@ -155,6 +160,7 @@ fn build_all_urls(
             name2url,
             map,
             unstable_opts,
+            seen,
         );
     }
 }
@@ -199,6 +205,7 @@ pub fn add_root_urls(
         &name2url,
         map,
         &mut unstable_opts,
+        &mut HashSet::new(),
     );
     let std_url = match &map.std {
         None | Some(RustdocExternMode::Remote) => None,

tests/testsuite/rustdoc_extern_html.rs

@@ -416,3 +416,50 @@ fn alt_sparse_registry() {
     let gold = p.read_file("target/doc/foo/fn.gold.html");
     assert!(gold.contains(r#"href="https://docs.rs/grimm/1.0.0/grimm/struct.Gold.html""#));
 }
+
+#[cargo_test(nightly, reason = "--extern-html-root-url is unstable")]
+fn same_deps_multi_occurrence_in_dep_tree() {
+    // rust-lang/cargo#13543
+    Package::new("baz", "1.0.0")
+        .file("src/lib.rs", "")
+        .publish();
+    Package::new("bar", "1.0.0")
+        .file("src/lib.rs", "")
+        .dep("baz", "1.0")
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                edition = "2018"
+
+                [dependencies]
+                bar = "1.0"
+                baz = "1.0"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            ".cargo/config.toml",
+            r#"
+                [doc.extern-map.registries]
+                crates-io = "https://docs.rs/"
+            "#,
+        )
+        .build();
+    p.cargo("doc -v --no-deps -Zrustdoc-map")
+        .masquerade_as_nightly_cargo(&["rustdoc-map"])
+        .with_stderr_does_not_contain(
+            "[..]--extern-html-root-url[..]bar=https://docs.rs\
+             [..]--extern-html-root-url[..]baz=https://docs.rs\
+             [..]--extern-html-root-url[..]baz=https://docs.rs[..]",
+        )
+        .with_stderr_contains(
+            "[..]--extern-html-root-url[..]bar=https://docs.rs\
+             [..]--extern-html-root-url[..]baz=https://docs.rs[..]",
+        )
+        .run();
+}