rustdoc::broken_intra_doc_links: only be lenient with shortcut links

collapsed links and reference links have a pretty particular syntax,
it seems unlikely they would show up on accident.

Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>

Author: lolbinarycat

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -944,9 +944,10 @@ fn preprocess_link(
     // certain link kinds cannot have their path be urls,
     // so they should not be ignored, no matter how much they look like urls.
     // e.g. [https://example.com/] is not a link to example.com.
-    let can_be_url = ori_link.kind != LinkType::ShortcutUnknown
-        && ori_link.kind != LinkType::CollapsedUnknown
-        && ori_link.kind != LinkType::ReferenceUnknown;
+    let can_be_url = !matches!(
+        ori_link.kind,
+        LinkType::ShortcutUnknown | LinkType::CollapsedUnknown | LinkType::ReferenceUnknown
+    );
 
     // [] is mostly likely not supposed to be a link
     if ori_link.link.is_empty() {
@@ -996,9 +997,25 @@ fn preprocess_link(
         }
     };
 
-    // If there's no backticks, be lenient revert to old behavior.
+    // If there's no backticks, be lenient and revert to the old behavior.
     // This is to prevent churn by linting on stuff that isn't meant to be a link.
-    if (can_be_url || !ori_link.link.contains('`')) && should_ignore_link(path_str) {
+    // only shortcut links have simple enough syntax that they
+    // are likely to be written accidentally, collapsed and reference links
+    // need 4 metachars, and reference links will not usually use
+    // backticks in the reference name.
+    // therefore, only shortcut syntax gets the lenient behavior.
+    //
+    // here's a truth table for how link kinds that cannot be urls are handled:
+    //
+    // |-------------------------------------------------------|
+    // |              |  is shortcut link  | not shortcut link |
+    // |--------------|--------------------|-------------------|
+    // | has backtick |    never ignore    |    never ignore   |
+    // | no backtick  | ignore if url-like |    never ignore   |
+    // |-------------------------------------------------------|
+    let ignore_urllike =
+        can_be_url || (ori_link.kind == LinkType::ShortcutUnknown && !ori_link.link.contains('`'));
+    if ignore_urllike && should_ignore_link(path_str) {
         return None;
     }
 

tests/rustdoc-ui/intra-doc/weird-syntax.rs

@@ -65,7 +65,7 @@ pub struct XLinkToCloneWithStartSpace;
 /// [x][struct@Clone ] //~ERROR link
 pub struct XLinkToCloneWithEndSpace;
 
-/// [x][Clone\(\)]
+/// [x][Clone\(\)] //~ERROR link
 pub struct XLinkToCloneWithEscapedParens;
 
 /// [x][`Clone`] not URL-shaped enough

tests/rustdoc-ui/intra-doc/weird-syntax.stderr

@@ -123,6 +123,14 @@ LL - /// [x][struct@Clone ]
 LL + /// [x][trait@Clone ]
    |
 
+error: unresolved link to `Clone\(\)`
+  --> $DIR/weird-syntax.rs:68:9
+   |
+LL | /// [x][Clone\(\)]
+   |         ^^^^^^^^^ no item named `Clone\(\)` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
 error: unresolved link to `Clone`
   --> $DIR/weird-syntax.rs:74:9
    |
@@ -299,5 +307,5 @@ LL | /// - [`SDL_PROP_WINDOW_CREATE_COCOA_WINDOW_POINTER`]: the
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
 
-error: aborting due to 27 previous errors
+error: aborting due to 28 previous errors