Fix relative extern URL depth on source pages

Signed-off-by: arferreira <arfs.antonio@gmail.com>

Author: arferreira

src/librustdoc/html/format.rs

@@ -403,7 +403,8 @@ fn generate_macro_def_id_path(
 
     let url = match cache.extern_locations[&def_id.krate] {
         ExternalLocation::Remote { ref url, is_absolute } => {
-            let mut prefix = remote_url_prefix(url, is_absolute, cx.current.len());
+            let depth = remote_item_depth(root_path, cx.current.len());
+            let mut prefix = remote_url_prefix(url, is_absolute, depth);
             prefix.extend(path.iter().copied());
             prefix.finish()
         }
@@ -460,8 +461,8 @@ fn generate_item_def_id_path(
     let shortty = ItemType::from_def_id(def_id, tcx);
     let module_fqp = to_module_fqp(shortty, &fqp);
 
-    let (parts, is_absolute) = url_parts(cx.cache(), def_id, module_fqp, &cx.current)?;
-    let mut url = make_href(root_path, shortty, parts, &fqp, is_absolute);
+    let (parts, is_remote) = url_parts(cx.cache(), def_id, module_fqp, &cx.current, root_path)?;
+    let mut url = make_href(root_path, shortty, parts, &fqp, is_remote);
 
     if def_id != original_def_id {
         let kind = ItemType::from_def_id(original_def_id, tcx);
@@ -494,6 +495,16 @@ fn to_module_fqp(shortty: ItemType, fqp: &[Symbol]) -> &[Symbol] {
     if shortty == ItemType::Module { fqp } else { &fqp[..fqp.len() - 1] }
 }
 
+/// Computes the directory depth for relative extern URL resolution.
+///
+/// Doc pages use `relative_to.len()` (the module nesting depth).
+/// Source pages (jump-to-def) live under `src/<crate_name>/` — a different directory
+/// hierarchy — so their depth is derived from `root_path` (e.g. `../../` → depth 2)
+/// rather than the module path.
+fn remote_item_depth(root_path: Option<&str>, doc_depth: usize) -> usize {
+    root_path.map(|rp| rp.matches("../").count()).unwrap_or(doc_depth)
+}
+
 fn remote_url_prefix(url: &str, is_absolute: bool, depth: usize) -> UrlPartsBuilder {
     let url = url.trim_end_matches('/');
     if is_absolute {
@@ -506,17 +517,27 @@ fn remote_url_prefix(url: &str, is_absolute: bool, depth: usize) -> UrlPartsBuil
     }
 }
 
+/// Returns `(url_parts, is_remote)` where `is_remote` indicates the URL points to an
+/// external location and should not be prefixed with `root_path`.
+///
+/// `root_path` is provided when generating URLs from source pages (jump-to-def).
+/// Source pages live under `src/<crate_name>/` and use a different depth than doc pages,
+/// so when present, we derive the depth from `root_path` instead of `relative_to`.
 fn url_parts(
     cache: &Cache,
     def_id: DefId,
     module_fqp: &[Symbol],
     relative_to: &[Symbol],
+    root_path: Option<&str>,
 ) -> Result<(UrlPartsBuilder, bool), HrefError> {
     match cache.extern_locations[&def_id.krate] {
         ExternalLocation::Remote { ref url, is_absolute } => {
-            let mut builder = remote_url_prefix(url, is_absolute, relative_to.len());
+            let depth = remote_item_depth(root_path, relative_to.len());
+            let mut builder = remote_url_prefix(url, is_absolute, depth);
             builder.extend(module_fqp.iter().copied());
-            Ok((builder, is_absolute))
+            // Remote URLs (both absolute and relative) already encode the correct path;
+            // they must not be prefixed with root_path.
+            Ok((builder, true))
         }
         ExternalLocation::Local => Ok((href_relative_parts(module_fqp, relative_to), false)),
         ExternalLocation::Unknown => Err(HrefError::DocumentationNotBuilt),
@@ -528,10 +549,11 @@ fn make_href(
     shortty: ItemType,
     mut url_parts: UrlPartsBuilder,
     fqp: &[Symbol],
-    is_absolute: bool,
+    is_remote: bool,
 ) -> String {
-    // FIXME: relative extern URLs may break when prefixed with root_path
-    if !is_absolute && let Some(root_path) = root_path {
+    // Remote URLs already have the correct depth via `remote_url_prefix`;
+    // only local items need `root_path` to bridge from source pages to the doc tree.
+    if !is_remote && let Some(root_path) = root_path {
         let root = root_path.trim_end_matches('/');
         url_parts.push_front(root);
     }
@@ -594,7 +616,7 @@ pub(crate) fn href_with_root_path(
         }
     }
 
-    let (fqp, shortty, url_parts, is_absolute) = match cache.paths.get(&did) {
+    let (fqp, shortty, url_parts, is_remote) = match cache.paths.get(&did) {
         Some(&(ref fqp, shortty)) => (
             fqp,
             shortty,
@@ -612,8 +634,9 @@ pub(crate) fn href_with_root_path(
             let def_id_to_get = if root_path.is_some() { original_did } else { did };
             if let Some(&(ref fqp, shortty)) = cache.external_paths.get(&def_id_to_get) {
                 let module_fqp = to_module_fqp(shortty, fqp);
-                let (parts, is_absolute) = url_parts(cache, did, module_fqp, relative_to)?;
-                (fqp, shortty, parts, is_absolute)
+                let (parts, is_remote) =
+                    url_parts(cache, did, module_fqp, relative_to, root_path)?;
+                (fqp, shortty, parts, is_remote)
             } else if matches!(def_kind, DefKind::Macro(_)) {
                 return generate_macro_def_id_path(did, cx, root_path);
             } else if did.is_local() {
@@ -624,7 +647,7 @@ pub(crate) fn href_with_root_path(
         }
     };
     Ok(HrefInfo {
-        url: make_href(root_path, shortty, url_parts, fqp, is_absolute),
+        url: make_href(root_path, shortty, url_parts, fqp, is_remote),
         kind: shortty,
         rust_path: fqp.clone(),
     })

tests/rustdoc-html/extern/extern-html-root-url-relative.rs

@@ -21,7 +21,11 @@ pub mod nested {
 pub mod intra_doc_link {
 }
 
-// link-to-definition
+// link-to-definition: source pages live under src/<crate_name>/ so they need
+// ../../ to reach the doc root. Previously these links were incorrectly generated
+// as ../../../ (one level too deep) which passed the `has` check by substring match.
 //@ has src/extern_html_root_url_relative/extern-html-root-url-relative.rs.html
 //@ has - '//a/@href' '../../core/iter/index.html'
 //@ has - '//a/@href' '../../core/future/index.html'
+//@ !has - '//a/@href' '../../../core/iter/index.html'
+//@ !has - '//a/@href' '../../../core/future/index.html'