enforce parsing invariant for patterns

crates/hir_def/src/macro_expansion_tests/mbe/tt_conversion.rs

@@ -141,7 +141,7 @@ macro_rules! m1 { () => (Some(x) left overs) }
 macro_rules! m2 { () => ($) }
 
 fn main() {
-    let Some(x) = ();
+    let Some(x)left overs = ();
     let /* parse error: expected pattern */
 $ = ();
 }

crates/parser/src/grammar.rs

@@ -109,6 +109,19 @@ pub(crate) mod entry {
             items::mod_contents(p, false);
             m.complete(p, MACRO_ITEMS);
         }
+
+        pub(crate) fn pattern(p: &mut Parser) {
+            let m = p.start();
+            patterns::pattern_single(p);
+            if p.at(EOF) {
+                m.abandon(p);
+                return;
+            }
+            while !p.at(EOF) {
+                p.bump_any();
+            }
+            m.complete(p, ERROR);
+        }
     }
 }
 

crates/parser/src/lib.rs

@@ -119,8 +119,8 @@ impl TopEntryPoint {
             TopEntryPoint::SourceFile => grammar::entry::top::source_file,
             TopEntryPoint::MacroStmts => grammar::entry::top::macro_stmts,
             TopEntryPoint::MacroItems => grammar::entry::top::macro_items,
+            TopEntryPoint::Pattern => grammar::entry::top::pattern,
             // FIXME
-            TopEntryPoint::Pattern => grammar::entry::prefix::pat,
             TopEntryPoint::Type => grammar::entry::prefix::ty,
             TopEntryPoint::Expr => grammar::entry::prefix::expr,
             TopEntryPoint::MetaItem => grammar::entry::prefix::meta_item,

crates/parser/src/tests/top_entries.rs

@@ -146,6 +146,33 @@ fn macro_pattern() {
               R_PAREN ")"
         "#]],
     );
+
+    check(
+        TopEntryPoint::Pattern,
+        "None leftover tokens",
+        expect![[r#"
+            ERROR
+              IDENT_PAT
+                NAME
+                  IDENT "None"
+              WHITESPACE " "
+              IDENT "leftover"
+              WHITESPACE " "
+              IDENT "tokens"
+        "#]],
+    );
+
+    check(
+        TopEntryPoint::Pattern,
+        "@err",
+        expect![[r#"
+            ERROR
+              ERROR
+                AT "@"
+              IDENT "err"
+            error 0: expected pattern
+        "#]],
+    );
 }
 
 #[track_caller]