2 files changed, 42 insertions, 0 deletions

diff --git a/crates/parser/src/grammar/type_args.rs b/crates/parser/src/grammar/type_args.rs
index 56266b8d4..be36cad17 100644
--- a/crates/parser/src/grammar/type_args.rs
+++ b/crates/parser/src/grammar/type_args.rs
@@ -25,6 +25,38 @@ pub(super) fn opt_generic_arg_list(p: &mut Parser, colon_colon_required: bool) {
     m.complete(p, GENERIC_ARG_LIST);
 }
 
+pub(super) fn const_arg(p: &mut Parser) {
+    let m = p.start();
+    // FIXME: duplicates the code below
+    match p.current() {
+        T!['{'] => {
+            expressions::block_expr(p);
+            m.complete(p, CONST_ARG);
+        }
+        k if k.is_literal() => {
+            expressions::literal(p);
+            m.complete(p, CONST_ARG);
+        }
+        T![true] | T![false] => {
+            expressions::literal(p);
+            m.complete(p, CONST_ARG);
+        }
+        T![-] => {
+            let lm = p.start();
+            p.bump(T![-]);
+            expressions::literal(p);
+            lm.complete(p, PREFIX_EXPR);
+            m.complete(p, CONST_ARG);
+        }
+        _ => {
+            let lm = p.start();
+            paths::use_path(p);
+            lm.complete(p, PATH_EXPR);
+            m.complete(p, CONST_ARG);
+        }
+    }
+}
+
 // test type_arg
 // type A = B<'static, i32, 1, { 2 }, Item=u64, true, false>;
 fn generic_arg(p: &mut Parser) {
diff --git a/crates/parser/src/grammar/type_params.rs b/crates/parser/src/grammar/type_params.rs
index 3de5248da..b1f979281 100644
--- a/crates/parser/src/grammar/type_params.rs
+++ b/crates/parser/src/grammar/type_params.rs
@@ -70,6 +70,16 @@ fn const_param(p: &mut Parser, m: Marker) {
     p.bump(T![const]);
     name(p);
     types::ascription(p);
+
+    // test const_param_defaults
+    // struct A<const N: i32 = -1>;
+    // struct B<const N: i32 = {}>;
+    // struct C<const N: i32 = some::CONST>;
+    if p.at(T![=]) {
+        p.bump(T![=]);
+        type_args::const_arg(p);
+    }
+
     m.complete(p, CONST_PARAM);
 }