feat: improve parser error recovery for function parameters

crates/parser/src/grammar/items/consts.rs

@@ -21,8 +21,11 @@ fn const_or_static(p: &mut Parser, m: Marker, kw: SyntaxKind, def: SyntaxKind) {
 
     // test_err static_underscore
     // static _: i32 = 5;
-
-    types::ascription(p);
+    if p.at(T![:]) {
+        types::ascription(p);
+    } else {
+        p.error("missing type for `const` or `static`")
+    }
     if p.eat(T![=]) {
         expressions::expr(p);
     }

crates/parser/src/grammar/params.rs

@@ -106,7 +106,13 @@ fn param(p: &mut Parser, m: Marker, flavor: Flavor) -> Variadic {
             if variadic_param(p) {
                 res = Variadic(true)
             } else {
-                types::ascription(p);
+                if p.at(T![:]) {
+                    types::ascription(p)
+                } else {
+                    // test_err missing_fn_param_type
+                    // fn f(x y: i32, z, t: i32) {}
+                    p.error("missing type for function parameter")
+                }
             }
         }
         // test value_parameters_no_patterns
@@ -126,7 +132,11 @@ fn param(p: &mut Parser, m: Marker, flavor: Flavor) -> Variadic {
                 if variadic_param(p) {
                     res = Variadic(true)
                 } else {
-                    types::ascription(p);
+                    if p.at(T![:]) {
+                        types::ascription(p)
+                    } else {
+                        p.error("missing type for function parameter")
+                    }
                 }
             } else {
                 types::type_(p);

crates/parser/src/grammar/type_params.rs

@@ -67,7 +67,11 @@ fn const_param(p: &mut Parser, m: Marker) {
     assert!(p.at(T![const]));
     p.bump(T![const]);
     name(p);
-    types::ascription(p);
+    if p.at(T![:]) {
+        types::ascription(p);
+    } else {
+        p.error("missing type for const parameter");
+    }
 
     // test const_param_defaults
     // struct A<const N: i32 = -1>;

crates/parser/src/grammar/types.rs

@@ -55,7 +55,8 @@ fn type_with_bounds_cond(p: &mut Parser, allow_bounds: bool) {
 }
 
 pub(super) fn ascription(p: &mut Parser) {
-    p.expect(T![:]);
+    assert!(p.at(T![:]));
+    p.bump(T![:]);
     type_(p)
 }