From e78424846eb29a2d25389364a0b866992bfe4f8d Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Sun, 2 Jan 2022 17:32:15 +0300
Subject: [PATCH] enforce parsing invariant for patterns

---
 .../mbe/tt_conversion.rs                      |  2 +-
 crates/parser/src/grammar.rs                  | 13 +++++++++
 crates/parser/src/lib.rs                      |  2 +-
 crates/parser/src/tests/top_entries.rs        | 27 +++++++++++++++++++
 4 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/crates/hir_def/src/macro_expansion_tests/mbe/tt_conversion.rs b/crates/hir_def/src/macro_expansion_tests/mbe/tt_conversion.rs
index 97c27c453b0..4c58ea9ba64 100644
--- a/crates/hir_def/src/macro_expansion_tests/mbe/tt_conversion.rs
+++ b/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 */
 $ = ();
 }
diff --git a/crates/parser/src/grammar.rs b/crates/parser/src/grammar.rs
index e1a265d817c..eee9a8c0cd5 100644
--- a/crates/parser/src/grammar.rs
+++ b/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);
+        }
     }
 }
 
diff --git a/crates/parser/src/lib.rs b/crates/parser/src/lib.rs
index c5014be6c33..5c0e997ea10 100644
--- a/crates/parser/src/lib.rs
+++ b/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,
diff --git a/crates/parser/src/tests/top_entries.rs b/crates/parser/src/tests/top_entries.rs
index fa25ffd0a26..48359150638 100644
--- a/crates/parser/src/tests/top_entries.rs
+++ b/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]