Correctly encode doc attribute metadata

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -549,6 +549,21 @@ pub struct DocAttribute {
     pub no_crate_inject: Option<Span>,
 }
 
+impl DocAttribute {
+    /// Returns `true` if contains `doc(inline)` and doesn't contain `doc(no_inline)`.
+    pub fn is_inline(&self) -> bool {
+        let mut is_no_inline = false;
+        let mut is_inline = false;
+        for (inline, _) in &self.inline {
+            match inline {
+                DocInline::Inline => is_inline = true,
+                DocInline::NoInline => is_no_inline = true,
+            }
+        }
+        is_inline && !is_no_inline
+    }
+}
+
 /// Represents parsed *built-in* inert attributes.
 ///
 /// ## Overview

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -880,7 +880,7 @@ fn analyze_attr(attr: &hir::Attribute, state: &mut AnalyzeAttrState<'_>) -> bool
     } else if let hir::Attribute::Parsed(AttributeKind::Doc(d)) = attr {
         // If this is a `doc` attribute that doesn't have anything except maybe `inline` (as in
         // `#[doc(inline)]`), then we can remove it. It won't be inlinable in downstream crates.
-        if d.inline.is_empty() {
+        if !d.is_inline() {
             should_encode = true;
             if d.hidden.is_some() {
                 state.is_doc_hidden = true;