rustdoc: Don't add "Read more" link if there is no extra content

src/librustdoc/html/markdown.rs

@@ -567,11 +567,12 @@ struct SummaryLine<'a, I: Iterator<Item = Event<'a>>> {
     inner: I,
     started: bool,
     depth: u32,
+    skipped_tags: u32,
 }
 
 impl<'a, I: Iterator<Item = Event<'a>>> SummaryLine<'a, I> {
     fn new(iter: I) -> Self {
-        SummaryLine { inner: iter, started: false, depth: 0 }
+        SummaryLine { inner: iter, started: false, depth: 0, skipped_tags: 0 }
     }
 }
 
@@ -601,13 +602,15 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for SummaryLine<'a, I> {
             let is_allowed_tag = match event {
                 Event::Start(ref c) => {
                     if is_forbidden_tag(c) {
+                        self.skipped_tags += 1;
                         return None;
                     }
                     self.depth += 1;
                     check_if_allowed_tag(c)
                 }
                 Event::End(ref c) => {
                     if is_forbidden_tag(c) {
+                        self.skipped_tags += 1;
                         return None;
                     }
                     self.depth -= 1;
@@ -616,6 +619,9 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for SummaryLine<'a, I> {
                 }
                 _ => true,
             };
+            if !is_allowed_tag {
+                self.skipped_tags += 1;
+            }
             return if !is_allowed_tag {
                 if is_start {
                     Some(Event::Start(Tag::Paragraph))
@@ -1096,11 +1102,11 @@ impl MarkdownItemInfo<'_> {
 }
 
 impl MarkdownSummaryLine<'_> {
-    pub(crate) fn into_string(self) -> String {
+    pub(crate) fn into_string_with_has_more_content(self) -> (String, bool) {
         let MarkdownSummaryLine(md, links) = self;
         // This is actually common enough to special-case
         if md.is_empty() {
-            return String::new();
+            return (String::new(), false);
         }
 
         let mut replacer = |broken_link: BrokenLink<'_>| {
@@ -1110,17 +1116,26 @@ impl MarkdownSummaryLine<'_> {
                 .map(|link| (link.href.as_str().into(), link.new_text.as_str().into()))
         };
 
-        let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer));
+        let p = Parser::new_with_broken_link_callback(md, summary_opts(), Some(&mut replacer))
+            .peekable();
+        let mut summary = SummaryLine::new(p);
 
         let mut s = String::new();
 
-        let without_paragraphs = LinkReplacer::new(SummaryLine::new(p), links).filter(|event| {
+        let without_paragraphs = LinkReplacer::new(&mut summary, links).filter(|event| {
             !matches!(event, Event::Start(Tag::Paragraph) | Event::End(Tag::Paragraph))
         });
 
         html::push_html(&mut s, without_paragraphs);
 
-        s
+        let has_more_content =
+            matches!(summary.inner.peek(), Some(Event::Start(_))) || summary.skipped_tags > 0;
+
+        (s, has_more_content)
+    }
+
+    pub(crate) fn into_string(self) -> String {
+        self.into_string_with_has_more_content().0
     }
 }
 

src/librustdoc/html/render/mod.rs

@@ -467,9 +467,10 @@ fn document_short(
         return;
     }
     if let Some(s) = item.doc_value() {
-        let mut summary_html = MarkdownSummaryLine(&s, &item.links(cx)).into_string();
+        let (mut summary_html, has_more_content) =
+            MarkdownSummaryLine(&s, &item.links(cx)).into_string_with_has_more_content();
 
-        if s.contains('\n') {
+        if has_more_content {
             let link = format!(r#" <a{}>Read more</a>"#, assoc_href_attr(item, link, cx));
 
             if let Some(idx) = summary_html.rfind("</p>") {

src/test/rustdoc/read-more-unneeded.rs

@@ -0,0 +1,34 @@
+// Regression test for https://github.com/rust-lang/rust/issues/105677.
+// This test ensures that the "Read more" link is only generated when
+// there is actually more documentation to read after the short summary.
+
+#![crate_name = "foo"]
+
+pub trait MyFrom {
+    /// # Hello
+    /// ## Yolo
+    /// more!
+    fn try_from1();
+    /// a
+    /// b
+    /// c
+    fn try_from2();
+    /// a
+    ///
+    /// b
+    ///
+    /// c
+    fn try_from3();
+}
+
+pub struct NonZero;
+
+// @has 'foo/struct.NonZero.html'
+impl MyFrom for NonZero {
+    // @matches - '//*[@class="docblock"]' '^Hello Read more$'
+    fn try_from1() {}
+    // @matches - '//*[@class="docblock"]' '^a\sb\sc$'
+    fn try_from2() {}
+    // @matches - '//*[@class="docblock"]' '^a Read more$'
+    fn try_from3() {}
+}

src/test/rustdoc/trait-impl.rs

@@ -30,8 +30,6 @@ impl Trait for Struct {
     // @has - '//*[@id="method.b"]/../../div[@class="docblock"]' 'These docs contain'
     // @has - '//*[@id="method.b"]/../../div[@class="docblock"]/a' 'reference link'
     // @has - '//*[@id="method.b"]/../../div[@class="docblock"]/a/@href' 'https://example.com'
-    // @has - '//*[@id="method.b"]/../../div[@class="docblock"]/a' 'Read more'
-    // @has - '//*[@id="method.b"]/../../div[@class="docblock"]/a/@href' 'trait.Trait.html#tymethod.b'
     fn b() {}
 
     // @!has - '//*[@id="method.c"]/../../div[@class="docblock"]' 'code block'