4 files changed, 141 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);
 }
 
diff --git a/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rast b/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rast
new file mode 100644
index 000000000..e8f40a4cd
--- /dev/null
+++ b/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rast
@@ -0,0 +1,96 @@
+[email protected]
+  [email protected]
+    [email protected] "struct"
+    [email protected] " "
+    [email protected]
+      [email protected] "A"
+    [email protected]
+      [email protected] "<"
+      [email protected]
+        [email protected] "const"
+        [email protected] " "
+        [email protected]
+          [email protected] "N"
+        [email protected] ":"
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected]
+              [email protected]
+                [email protected] "i32"
+        [email protected] " "
+        [email protected] "="
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected] "-"
+            [email protected]
+              [email protected] "1"
+      [email protected] ">"
+    [email protected] ";"
+  [email protected] "\n"
+  [email protected]
+    [email protected] "struct"
+    [email protected] " "
+    [email protected]
+      [email protected] "B"
+    [email protected]
+      [email protected] "<"
+      [email protected]
+        [email protected] "const"
+        [email protected] " "
+        [email protected]
+          [email protected] "N"
+        [email protected] ":"
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected]
+              [email protected]
+                [email protected] "i32"
+        [email protected] " "
+        [email protected] "="
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected] "{"
+            [email protected] "}"
+      [email protected] ">"
+    [email protected] ";"
+  [email protected] "\n"
+  [email protected]
+    [email protected] "struct"
+    [email protected] " "
+    [email protected]
+      [email protected] "C"
+    [email protected]
+      [email protected] "<"
+      [email protected]
+        [email protected] "const"
+        [email protected] " "
+        [email protected]
+          [email protected] "N"
+        [email protected] ":"
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected]
+              [email protected]
+                [email protected] "i32"
+        [email protected] " "
+        [email protected] "="
+        [email protected] " "
+        [email protected]
+          [email protected]
+            [email protected]
+              [email protected]
+                [email protected]
+                  [email protected]
+                    [email protected] "some"
+              [email protected] "::"
+              [email protected]
+                [email protected]
+                  [email protected] "CONST"
+      [email protected] ">"
+    [email protected] ";"
+  [email protected] "\n"
diff --git a/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rs b/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rs
new file mode 100644
index 000000000..68388c8fb
--- /dev/null
+++ b/crates/syntax/test_data/parser/inline/ok/0165_const_param_defaults.rs
@@ -0,0 +1,3 @@
+struct A<const N: i32 = -1>;
+struct B<const N: i32 = {}>;
+struct C<const N: i32 = some::CONST>;