Prefer doc comments over //-comments in compiler

compiler/rustc_expand/src/base.rs

@@ -242,8 +242,8 @@ pub enum ExpandResult<T, U> {
     Retry(U),
 }
 
-// `meta_item` is the attribute, and `item` is the item being modified.
 pub trait MultiItemModifier {
+    /// `meta_item` is the attribute, and `item` is the item being modified.
     fn expand(
         &self,
         ecx: &mut ExtCtxt<'_>,

compiler/rustc_expand/src/build.rs

@@ -193,7 +193,7 @@ impl<'a> ExtCtxt<'a> {
         self.stmt_local(local, sp)
     }
 
-    // Generates `let _: Type;`, which is usually used for type assertions.
+    /// Generates `let _: Type;`, which is usually used for type assertions.
     pub fn stmt_let_type_only(&self, span: Span, ty: P<ast::Ty>) -> ast::Stmt {
         let local = P(ast::Local {
             pat: self.pat_wild(span),

compiler/rustc_expand/src/config.rs

@@ -200,7 +200,7 @@ fn get_features(
     features
 }
 
-// `cfg_attr`-process the crate's attributes and compute the crate's features.
+/// `cfg_attr`-process the crate's attributes and compute the crate's features.
 pub fn features(
     sess: &Session,
     mut krate: ast::Crate,

compiler/rustc_expand/src/expand.rs

@@ -401,7 +401,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         krate
     }
 
-    // Recursively expand all macro invocations in this AST fragment.
+    /// Recursively expand all macro invocations in this AST fragment.
     pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragment {
         let orig_expansion_data = self.cx.current_expansion.clone();
         let orig_force_mode = self.cx.force_mode;
@@ -1931,9 +1931,12 @@ pub struct ExpansionConfig<'feat> {
     pub features: Option<&'feat Features>,
     pub recursion_limit: Limit,
     pub trace_mac: bool,
-    pub should_test: bool,          // If false, strip `#[test]` nodes
-    pub span_debug: bool,           // If true, use verbose debugging for `proc_macro::Span`
-    pub proc_macro_backtrace: bool, // If true, show backtraces for proc-macro panics
+    /// If false, strip `#[test]` nodes
+    pub should_test: bool,
+    /// If true, use verbose debugging for `proc_macro::Span`
+    pub span_debug: bool,
+    /// If true, show backtraces for proc-macro panics
+    pub proc_macro_backtrace: bool,
 }
 
 impl<'feat> ExpansionConfig<'feat> {