improve maybe_consume_incorrect_semicolon

compiler/rustc_ast/src/ast.rs

@@ -3250,6 +3250,7 @@ pub enum ItemKind {
 }
 
 impl ItemKind {
+    /// "a" or "an"
     pub fn article(&self) -> &'static str {
         use ItemKind::*;
         match self {

compiler/rustc_parse/src/errors.rs

@@ -83,7 +83,7 @@ pub(crate) struct IncorrectSemicolon<'a> {
     #[suggestion(style = "short", code = "", applicability = "machine-applicable")]
     pub span: Span,
     #[help]
-    pub opt_help: Option<()>,
+    pub show_help: bool,
     pub name: &'a str,
 }
 

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1817,34 +1817,31 @@ pub(super) fn maybe_recover_from_bad_qpath_stage_2<T: RecoverQPath>(
         Ok(P(T::recovered(Some(P(QSelf { ty, path_span, position: 0 })), path)))
     }
 
-    pub fn maybe_consume_incorrect_semicolon(&mut self, items: &[P<Item>]) -> bool {
-        if self.token.kind == TokenKind::Semi {
-            self.bump();
+    /// This function gets called in places where a semicolon is NOT expected and if there's a
+    /// semicolon it emits the appropriate error and returns true.
+    pub fn maybe_consume_incorrect_semicolon(&mut self, previous_item: Option<&Item>) -> bool {
+        if self.token.kind != TokenKind::Semi {
+            return false;
+        }
 
-            let mut err =
-                IncorrectSemicolon { span: self.prev_token.span, opt_help: None, name: "" };
-
-            if !items.is_empty() {
-                let previous_item = &items[items.len() - 1];
-                let previous_item_kind_name = match previous_item.kind {
+        // Check previous item to add it to the diagnostic, for example to say
+        // `enum declarations are not followed by a semicolon`
+        let err = match previous_item {
+            Some(previous_item) => {
+                let name = match previous_item.kind {
                     // Say "braced struct" because tuple-structs and
                     // braceless-empty-struct declarations do take a semicolon.
-                    ItemKind::Struct(..) => Some("braced struct"),
-                    ItemKind::Enum(..) => Some("enum"),
-                    ItemKind::Trait(..) => Some("trait"),
-                    ItemKind::Union(..) => Some("union"),
-                    _ => None,
+                    ItemKind::Struct(..) => "braced struct",
+                    _ => previous_item.kind.descr(),
                 };
-                if let Some(name) = previous_item_kind_name {
-                    err.opt_help = Some(());
-                    err.name = name;
-                }
+                IncorrectSemicolon { span: self.token.span, name, show_help: true }
             }
-            self.dcx().emit_err(err);
-            true
-        } else {
-            false
-        }
+            None => IncorrectSemicolon { span: self.token.span, name: "", show_help: false },
+        };
+        self.dcx().emit_err(err);
+
+        self.bump();
+        true
     }
 
     /// Creates a `Diag` for an unexpected token `t` and tries to recover if it is a

compiler/rustc_parse/src/parser/item.rs

@@ -59,13 +59,13 @@ pub fn parse_mod(
         let post_attr_lo = self.token.span;
         let mut items = ThinVec::new();
         while let Some(item) = self.parse_item(ForceCollect::No)? {
+            self.maybe_consume_incorrect_semicolon(Some(&item));
             items.push(item);
-            self.maybe_consume_incorrect_semicolon(&items);
         }
 
         if !self.eat(term) {
             let token_str = super::token_descr(&self.token);
-            if !self.maybe_consume_incorrect_semicolon(&items) {
+            if !self.maybe_consume_incorrect_semicolon(items.last().map(|x| &**x)) {
                 let msg = format!("expected item, found {token_str}");
                 let mut err = self.dcx().struct_span_err(self.token.span, msg);
                 let span = self.token.span;

src/librustdoc/doctest.rs

@@ -686,9 +686,9 @@ pub(crate) fn make_test(
                     }
                 }
 
-                // The supplied slice is only used for diagnostics,
+                // The supplied item is only used for diagnostics,
                 // which are swallowed here anyway.
-                parser.maybe_consume_incorrect_semicolon(&[]);
+                parser.maybe_consume_incorrect_semicolon(None);
             }
 
             // Reset errors so that they won't be reported as compiler bugs when dropping the

tests/ui/suggestions/recover-from-semicolon-trailing-item.stderr

@@ -3,6 +3,8 @@ error: expected item, found `;`
    |
 LL | mod M {};
    |         ^ help: remove this semicolon
+   |
+   = help: module declarations are not followed by a semicolon
 
 error: expected item, found `;`
   --> $DIR/recover-from-semicolon-trailing-item.rs:4:12
@@ -17,6 +19,8 @@ error: expected item, found `;`
    |
 LL | fn foo(a: usize) {};
    |                    ^ help: remove this semicolon
+   |
+   = help: function declarations are not followed by a semicolon
 
 error[E0308]: mismatched types
   --> $DIR/recover-from-semicolon-trailing-item.rs:10:20