fix assertione error on block parsing

crates/libsyntax2/src/grammar/expressions/atom.rs

@@ -148,11 +148,7 @@ fn lambda_expr(p: &mut Parser) -> CompletedMarker {
     p.eat(MOVE_KW);
     params::param_list_opt_types(p);
     if opt_fn_ret_type(p) {
-        if p.at(L_CURLY) {
-            block(p);
-        } else {
-            p.error("expected a block");
-        }
+        block(p);
     } else {
         expr(p);
     }

crates/libsyntax2/src/grammar/expressions/mod.rs

@@ -26,7 +26,10 @@ fn expr_no_struct(p: &mut Parser) {
 // fn c() { 1; 2; }
 // fn d() { 1; 2 }
 pub(crate) fn block(p: &mut Parser) {
-    assert!(p.at(L_CURLY));
+    if !p.at(L_CURLY) {
+        p.error("expected a block");
+        return;
+    }
     let m = p.start();
     p.bump();
     while !p.at(EOF) && !p.at(R_CURLY) {

crates/libsyntax2/src/grammar/items/mod.rs

@@ -252,10 +252,10 @@ fn function(p: &mut Parser, flavor: ItemFlavor) {
 
     // test fn_decl
     // trait T { fn foo(); }
-    if p.at(L_CURLY) {
-        expressions::block(p);
+    if p.at(SEMI) {
+        p.bump();
     } else {
-        p.expect(SEMI);
+        expressions::block(p)
     }
 }
 

crates/libsyntax2/tests/data/parser/err/0015_curly_in_params.txt

@@ -8,7 +8,7 @@ ROOT@[0; 14)
       L_PAREN@[6; 7)
       err: `expected value parameter`
       err: `expected R_PAREN`
-      err: `expected SEMI`
+      err: `expected a block`
       err: `expected an item`
   ERROR@[7; 8)
     R_CURLY@[7; 8)