Add test cases for intra-doc links

src/librustdoc/html/format.rs

@@ -532,6 +532,7 @@ fn make_href(
     fqp: &[Symbol],
     is_absolute: bool,
 ) -> String {
+    // FIXME: relative extern URLs may break when prefixed with root_path
     if !is_absolute && let Some(root_path) = root_path {
         let root = root_path.trim_end_matches('/');
         url_parts.push_front(root);

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

@@ -1,4 +1,4 @@
-//@ compile-flags:-Z unstable-options --extern-html-root-url core=../ --extern-html-root-takes-precedence
+//@ compile-flags:-Z unstable-options --extern-html-root-url core=../ --extern-html-root-takes-precedence --generate-link-to-definition
 
 // At depth 1 (top-level), the href should be ../core/...
 //@ has extern_html_root_url_relative/index.html
@@ -9,7 +9,19 @@
 // At depth 2 (inside a module), the href should be ../../core/...
 pub mod nested {
     //@ has extern_html_root_url_relative/nested/index.html
-    //@ has - '//a/@href' '../../core/iter/index.html'
+    //@ has - '//a/@href' '../../core/future/index.html'
     #[doc(no_inline)]
-    pub use std::iter;
+    pub use std::future;
 }
+
+// Also depth 2, but for an intra-doc link.
+//@ has extern_html_root_url_relative/intra_doc_link/index.html
+//@ has - '//a/@href' '../../core/ptr/fn.write.html'
+/// [write](<core::ptr::write()>)
+pub mod intra_doc_link {
+}
+
+// link-to-definition
+//@ 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'