Fix intra-doc links on pub re-exports

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -578,6 +578,9 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
         let parent_node = if item.is_fake() {
             // FIXME: is this correct?
             None
+        // If we're documenting the crate root itself, it has no parent. Use the root instead.
+        } else if item.def_id.is_top_level_module() {
+            Some(item.def_id)
         } else {
             let mut current = item.def_id;
             // The immediate parent might not always be a module.
@@ -589,6 +592,12 @@ impl<'a, 'tcx> DocFolder for LinkCollector<'a, 'tcx> {
                     }
                     current = parent;
                 } else {
+                    debug!(
+                        "{:?} has no parent (kind={:?}, original was {:?})",
+                        current,
+                        self.cx.tcx.def_kind(current),
+                        item.def_id
+                    );
                     break None;
                 }
             }

src/test/rustdoc/auxiliary/intra-link-pub-use.rs

@@ -0,0 +1,4 @@
+#![crate_name = "inner"]
+
+/// Documentation, including a link to [std::ptr]
+pub fn f() {}

src/test/rustdoc/intra-link-pub-use.rs

@@ -0,0 +1,27 @@
+// aux-build: intra-link-pub-use.rs
+#![deny(broken_intra_doc_links)]
+#![crate_name = "outer"]
+
+extern crate inner;
+
+/// [mod@std::env] [g]
+
+// FIXME: This can't be tested because rustdoc doesn't show documentation on pub re-exports.
+// Until then, comment out the `htmldocck` test.
+// This test still does something; namely check that no incorrect errors are emitted when
+// documenting the re-export.
+
+// @has outer/index.html
+// @ has - '//a[@href="https://doc.rust-lang.org/nightly/std/env/fn.var.html"]' "std::env"
+// @ has - '//a[@href="../outer/fn.f.html"]' "g"
+pub use f as g;
+
+// FIXME: same as above
+/// [std::env]
+extern crate self as _;
+
+// Make sure the documentation is actually correct by documenting an inlined re-export
+/// [mod@std::env]
+// @has outer/fn.f.html
+// @has - '//a[@href="https://doc.rust-lang.org/nightly/std/env/index.html"]' "std::env"
+pub use inner::f;