3 files changed, 35 insertions, 4 deletions

diff --git a/crates/parser/src/grammar/expressions/atom.rs b/crates/parser/src/grammar/expressions/atom.rs
index e897d5a52..c7a3556a7 100644
--- a/crates/parser/src/grammar/expressions/atom.rs
+++ b/crates/parser/src/grammar/expressions/atom.rs
@@ -46,6 +46,7 @@ pub(super) const ATOM_EXPR_FIRST: TokenSet =
         T![continue],
         T![async],
         T![try],
+        T![const],
         T![loop],
         T![for],
         LIFETIME_IDENT,
@@ -115,6 +116,14 @@ pub(super) fn atom_expr(p: &mut Parser, r: Restrictions) -> Option<(CompletedMar
             block_expr(p);
             m.complete(p, EFFECT_EXPR)
         }
+        // test const_block
+        // fn f() { const { } }
+        T![const] if la == T!['{'] => {
+            let m = p.start();
+            p.bump(T![const]);
+            block_expr(p);
+            m.complete(p, EFFECT_EXPR)
+        }
         T!['{'] => {
             // test for_range_from
             // fn foo() {
diff --git a/crates/parser/src/grammar/items.rs b/crates/parser/src/grammar/items.rs
index 8999829b4..cf4168d32 100644
--- a/crates/parser/src/grammar/items.rs
+++ b/crates/parser/src/grammar/items.rs
@@ -96,7 +96,10 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
     let mut has_mods = false;
 
     // modifiers
-    has_mods |= p.eat(T![const]);
+    if p.at(T![const]) && p.nth(1) != T!['{'] {
+        p.eat(T![const]);
+        has_mods = true;
+    }
 
     // test_err async_without_semicolon
     // fn foo() { let _ = async {} }
@@ -167,7 +170,7 @@ pub(super) fn maybe_item(p: &mut Parser, m: Marker) -> Result<(), Marker> {
             m.complete(p, TRAIT);
         }
 
-        T![const] => {
+        T![const] if p.nth(1) != T!['{'] => {
             consts::konst(p, m);
         }
 
@@ -386,10 +389,15 @@ fn macro_rules(p: &mut Parser, m: Marker) {
     }
 
     match p.current() {
-        T!['{'] => {
+        // test macro_rules_non_brace
+        // macro_rules! m ( ($i:ident) => {} );
+        // macro_rules! m [ ($i:ident) => {} ];
+        T!['['] | T!['('] => {
             token_tree(p);
+            p.expect(T![;]);
         }
-        _ => p.error("expected `{`"),
+        T!['{'] => token_tree(p),
+        _ => p.error("expected `{`, `[`, `(`"),
     }
     m.complete(p, MACRO_RULES);
 }
diff --git a/crates/parser/src/grammar/patterns.rs b/crates/parser/src/grammar/patterns.rs
index 7e7f73dee..b53d5749f 100644
--- a/crates/parser/src/grammar/patterns.rs
+++ b/crates/parser/src/grammar/patterns.rs
@@ -89,6 +89,7 @@ fn atom_pat(p: &mut Parser, recovery_set: TokenSet) -> Option<CompletedMarker> {
     let m = match p.nth(0) {
         T![box] => box_pat(p),
         T![ref] | T![mut] => ident_pat(p, true),
+        T![const] => const_block_pat(p),
         IDENT => match p.nth(1) {
             // Checks the token after an IDENT to see if a pattern is a path (Struct { .. }) or macro
             // (T![x]).
@@ -386,3 +387,16 @@ fn box_pat(p: &mut Parser) -> CompletedMarker {
     pattern_single(p);
     m.complete(p, BOX_PAT)
 }
+
+// test const_block_pat
+// fn main() {
+//     let const { 15 } = ();
+//     let const { foo(); bar() } = ();
+// }
+fn const_block_pat(p: &mut Parser) -> CompletedMarker {
+    assert!(p.at(T![const]));
+    let m = p.start();
+    p.bump(T![const]);
+    expressions::block_expr(p);
+    m.complete(p, CONST_BLOCK_PAT)
+}