diff --git a/contributing/grammar.md b/contributing/grammar.md
index 240f4ef..ee3e1a5 100644
--- a/contributing/grammar.md
+++ b/contributing/grammar.md
@@ -111,7 +111,7 @@ flag_long       → "--" flag_name;
 short_flag      → "-" SHORT_FLAGS ;
 spread         → "..." expression ;
 
-command_name    → string | call_name | IDENTIFIER ;
+command_name    → string | IDENTIFIER_ALLOW_DASH ;
 flag_name      → IDENTIFIER_ALLOW_DASH ;
 call_name
                → IDENTIFIER_ALLOW_DASH IDENTIFIER_ALLOW_DASH+ ;
diff --git a/src/parser.rs b/src/parser.rs
index 71046e3..e0abf5c 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -308,12 +308,23 @@ pub enum AstNode {
         long: NodeId,
         short: Option<NodeId>,
         ty: Option<NodeId>,
+        // it can only exists if `ty` is not None
+        custom_completion: Option<NodeId>,
         default: Option<NodeId>,
     },
     PosParam {
         name: NodeId,
         ty: Option<NodeId>,
+        // it can only exists if `ty` is not None
+        custom_completion: Option<NodeId>,
         default: Option<NodeId>,
+        is_optional: bool,
+    },
+    RestParam {
+        name: NodeId,
+        ty: Option<NodeId>,
+        // it can only exists if `ty` is not None
+        custom_completion: Option<NodeId>,
     },
     InOutTypes(InOutTypesId),
     /// Input/output type pair for a command
@@ -1000,6 +1011,13 @@ impl Parser {
         )
     }
 
+    pub fn command_name(&mut self) -> NodeId {
+        match self.tokens.peek_token() {
+            Token::DoubleQuotedString | Token::SingleQuotedString => self.string(),
+            _ => self.identifier_allow_dash(),
+        }
+    }
+
     pub fn string(&mut self) -> NodeId {
         match self.tokens.peek() {
             (Token::DoubleQuotedString, span) => self.advance_node(AstNode::String, span),
@@ -1218,8 +1236,16 @@ impl Parser {
                 }
 
                 let is_flag_param = self.is_dashdash();
+                let is_rest_param = self.is_dotdotdot();
+                let mut is_pos_param_optional = false;
+
                 let (name, short_name) =
-                    if is_flag_param && matches!(params_context, ParamsContext::Squares) {
+                    if is_rest_param && matches!(params_context, ParamsContext::Squares) {
+                        // reset parameter
+                        self.tokens.advance();
+                        (self.name(), None)
+                    } else if is_flag_param && matches!(params_context, ParamsContext::Squares) {
+                        // flag_parameter.
                         let result = self.flag_long();
                         if self.is_lparen() {
                             self.tokens.advance();
@@ -1230,16 +1256,30 @@ impl Parser {
                             (result, None)
                         }
                     } else {
-                        (self.name(), None)
+                        // positional parameter
+                        let result = (self.name(), None);
+                        if self.is_question_mark() {
+                            self.tokens.advance();
+                            is_pos_param_optional = true;
+                        }
+                        result
                     };
 
-                let ty = if self.is_colon() {
+                let (ty, custom_completion) = if self.is_colon() {
                     // We have a type
                     self.colon();
 
-                    Some(self.typename())
+                    let type_name = self.typename();
+                    // We have custom completer
+                    let custom_completion = if self.is_at() {
+                        self.tokens.advance();
+                        Some(self.command_name())
+                    } else {
+                        None
+                    };
+                    (Some(type_name), custom_completion)
                 } else {
-                    None
+                    (None, None)
                 };
 
                 let default_val = if self.is_equals() {
@@ -1262,17 +1302,30 @@ impl Parser {
                             long: name,
                             short: short_name,
                             ty,
+                            custom_completion,
                             default: default_val,
                         },
                         name_span.start,
                         param_span_end,
                     )
+                } else if is_rest_param {
+                    self.create_node(
+                        AstNode::RestParam {
+                            name,
+                            ty,
+                            custom_completion,
+                        },
+                        name_span.start,
+                        param_span_end,
+                    )
                 } else {
                     self.create_node(
                         AstNode::PosParam {
                             name,
                             ty,
+                            custom_completion,
                             default: default_val,
+                            is_optional: is_pos_param_optional,
                         },
                         name_span.start,
                         param_span_end,
@@ -1868,6 +1921,10 @@ impl Parser {
         self.tokens.peek_token() == Token::Equals
     }
 
+    pub fn is_at(&mut self) -> bool {
+        self.tokens.peek_token() == Token::At
+    }
+
     pub fn is_comma(&mut self) -> bool {
         self.tokens.peek_token() == Token::Comma
     }
@@ -1956,6 +2013,10 @@ impl Parser {
         self.tokens.peek_token() == Token::DotDot
     }
 
+    pub fn is_dotdotdot(&mut self) -> bool {
+        self.tokens.peek_token() == Token::DotDotDot
+    }
+
     pub fn is_coloncolon(&mut self) -> bool {
         self.tokens.peek_token() == Token::ColonColon
     }
diff --git a/src/resolver.rs b/src/resolver.rs
index 57ef9c5..f64b92a 100644
--- a/src/resolver.rs
+++ b/src/resolver.rs
@@ -301,14 +301,18 @@ impl<'a> Resolver<'a> {
                         AstNode::PosParam {
                             name,
                             ty,
+                            custom_completion: _,
                             default: _,
+                            is_optional: _,
                         }
                         | AstNode::FlagParam {
                             long: name,
                             short: _,
                             ty,
+                            custom_completion: _,
                             default: _,
-                        } => {
+                        }
+                        | AstNode::RestParam { name, ty, .. } => {
                             self.define_variable(name, false);
                             if let Some(ty) = ty {
                                 self.resolve_node(ty);
diff --git a/src/snapshots/new_nu_parser__test__node_output@calls.nu.snap b/src/snapshots/new_nu_parser__test__node_output@calls.nu.snap
index 48e7a5a..8587cd0 100644
--- a/src/snapshots/new_nu_parser__test__node_output@calls.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@calls.nu.snap
@@ -16,15 +16,15 @@ input_file: tests/calls.nu
 9: Name (38 to 39) "a"
 10: Name (41 to 47) "string"
 11: Type { name: NodeId(10), args: None, optional: false } (41 to 47)
-12: PosParam { name: NodeId(9), ty: Some(NodeId(11)), default: None } (38 to 47)
+12: PosParam { name: NodeId(9), ty: Some(NodeId(11)), custom_completion: None, default: None, is_optional: false } (38 to 47)
 13: Name (49 to 50) "b"
 14: Name (52 to 58) "string"
 15: Type { name: NodeId(14), args: None, optional: false } (52 to 58)
-16: PosParam { name: NodeId(13), ty: Some(NodeId(15)), default: None } (49 to 58)
+16: PosParam { name: NodeId(13), ty: Some(NodeId(15)), custom_completion: None, default: None, is_optional: false } (49 to 58)
 17: Name (60 to 61) "c"
 18: Name (63 to 66) "int"
 19: Type { name: NodeId(18), args: None, optional: false } (63 to 66)
-20: PosParam { name: NodeId(17), ty: Some(NodeId(19)), default: None } (60 to 66)
+20: PosParam { name: NodeId(17), ty: Some(NodeId(19)), custom_completion: None, default: None, is_optional: false } (60 to 66)
 21: Params(ParamsId(0)) (37 to 67)
 22: Variable (72 to 74) "$a"
 23: Variable (76 to 78) "$b"
diff --git a/src/snapshots/new_nu_parser__test__node_output@calls_invalid.nu.snap b/src/snapshots/new_nu_parser__test__node_output@calls_invalid.nu.snap
index 653d079..2b08a20 100644
--- a/src/snapshots/new_nu_parser__test__node_output@calls_invalid.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@calls_invalid.nu.snap
@@ -8,7 +8,7 @@ input_file: tests/calls_invalid.nu
 1: Name (10 to 11) "a"
 2: Name (13 to 16) "int"
 3: Type { name: NodeId(2), args: None, optional: false } (13 to 16)
-4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), default: None } (10 to 16)
+4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), custom_completion: None, default: None, is_optional: false } (10 to 16)
 5: Params(ParamsId(0)) (8 to 18)
 6: Block(BlockId(0)) (19 to 21)
 7: Def { name: NodeId(0), type_params: None, params: NodeId(5), in_out_types: None, block: NodeId(6), env: false, wrapped: false } (0 to 21)
diff --git a/src/snapshots/new_nu_parser__test__node_output@closure.nu.snap b/src/snapshots/new_nu_parser__test__node_output@closure.nu.snap
index 3af804e..35e2139 100644
--- a/src/snapshots/new_nu_parser__test__node_output@closure.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@closure.nu.snap
@@ -5,9 +5,9 @@ input_file: tests/closure.nu
 ---
 ==== COMPILER ====
 0: Name (3 to 4) "a"
-1: PosParam { name: NodeId(0), ty: None, default: None } (3 to 4)
+1: PosParam { name: NodeId(0), ty: None, custom_completion: None, default: None, is_optional: false } (3 to 4)
 2: Name (6 to 7) "b"
-3: PosParam { name: NodeId(2), ty: None, default: None } (6 to 7)
+3: PosParam { name: NodeId(2), ty: None, custom_completion: None, default: None, is_optional: false } (6 to 7)
 4: Params(ParamsId(0)) (2 to 8)
 5: Variable (9 to 11) "$a"
 6: Plus (12 to 13)
diff --git a/src/snapshots/new_nu_parser__test__node_output@closure3.nu.snap b/src/snapshots/new_nu_parser__test__node_output@closure3.nu.snap
index dfaafc0..595cd3a 100644
--- a/src/snapshots/new_nu_parser__test__node_output@closure3.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@closure3.nu.snap
@@ -8,11 +8,11 @@ input_file: tests/closure3.nu
 1: Name (16 to 17) "a"
 2: Name (19 to 22) "int"
 3: Type { name: NodeId(2), args: None, optional: false } (19 to 22)
-4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), default: None } (16 to 22)
+4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), custom_completion: None, default: None, is_optional: false } (16 to 22)
 5: Name (24 to 25) "b"
 6: Name (27 to 30) "int"
 7: Type { name: NodeId(6), args: None, optional: false } (27 to 30)
-8: PosParam { name: NodeId(5), ty: Some(NodeId(7)), default: None } (24 to 30)
+8: PosParam { name: NodeId(5), ty: Some(NodeId(7)), custom_completion: None, default: None, is_optional: false } (24 to 30)
 9: Params(ParamsId(0)) (15 to 31)
 10: Variable (32 to 34) "$a"
 11: Plus (35 to 36)
diff --git a/src/snapshots/new_nu_parser__test__node_output@def.nu.snap b/src/snapshots/new_nu_parser__test__node_output@def.nu.snap
index 55106c7..b750ca1 100644
--- a/src/snapshots/new_nu_parser__test__node_output@def.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@def.nu.snap
@@ -6,11 +6,11 @@ input_file: tests/def.nu
 ==== COMPILER ====
 0: Name (4 to 7) "foo"
 1: Name (9 to 10) "w"
-2: PosParam { name: NodeId(1), ty: None, default: None } (9 to 10)
+2: PosParam { name: NodeId(1), ty: None, custom_completion: None, default: None, is_optional: false } (9 to 10)
 3: Name (11 to 12) "x"
 4: Name (14 to 17) "int"
 5: Type { name: NodeId(4), args: None, optional: false } (14 to 17)
-6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), default: None } (11 to 17)
+6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), custom_completion: None, default: None, is_optional: false } (11 to 17)
 7: Name (19 to 20) "y"
 8: Name (22 to 26) "list"
 9: Name (27 to 31) "list"
@@ -20,18 +20,18 @@ input_file: tests/def.nu
 13: Type { name: NodeId(9), args: Some(NodeId(12)), optional: false } (27 to 31)
 14: TypeArgs(TypeArgsId(1)) (26 to 37)
 15: Type { name: NodeId(8), args: Some(NodeId(14)), optional: false } (22 to 26)
-16: PosParam { name: NodeId(7), ty: Some(NodeId(15)), default: None } (19 to 26)
+16: PosParam { name: NodeId(7), ty: Some(NodeId(15)), custom_completion: None, default: None, is_optional: false } (19 to 26)
 17: Name (39 to 40) "z"
 18: Name (42 to 48) "record"
 19: Name (49 to 50) "a"
-20: PosParam { name: NodeId(19), ty: None, default: None } (49 to 50)
+20: PosParam { name: NodeId(19), ty: None, custom_completion: None, default: None, is_optional: false } (49 to 50)
 21: Name (52 to 53) "b"
 22: Name (55 to 58) "int"
 23: Type { name: NodeId(22), args: None, optional: false } (55 to 58)
-24: PosParam { name: NodeId(21), ty: Some(NodeId(23)), default: None } (52 to 58)
+24: PosParam { name: NodeId(21), ty: Some(NodeId(23)), custom_completion: None, default: None, is_optional: false } (52 to 58)
 25: Params(ParamsId(0)) (48 to 59)
 26: RecordType { fields: NodeId(25), optional: false } (42 to 60)
-27: PosParam { name: NodeId(17), ty: Some(NodeId(26)), default: None } (39 to 60)
+27: PosParam { name: NodeId(17), ty: Some(NodeId(26)), custom_completion: None, default: None, is_optional: false } (39 to 60)
 28: Params(ParamsId(1)) (8 to 61)
 29: Variable (66 to 68) "$w"
 30: Variable (69 to 71) "$x"
@@ -46,18 +46,18 @@ input_file: tests/def.nu
 39: Name (125 to 128) "int"
 40: Type { name: NodeId(39), args: None, optional: false } (125 to 128)
 41: Int (131 to 132) "3"
-42: FlagParam { long: NodeId(38), short: None, ty: Some(NodeId(40)), default: Some(NodeId(41)) } (118 to 132)
+42: FlagParam { long: NodeId(38), short: None, ty: Some(NodeId(40)), custom_completion: None, default: Some(NodeId(41)) } (118 to 132)
 43: Name (136 to 139) "baz"
 44: FlagLong(NodeId(43)) (134 to 139)
 45: Name (141 to 142) "b"
 46: FlagShort(NodeId(45)) (140 to 142)
-47: FlagParam { long: NodeId(44), short: Some(NodeId(46)), ty: None, default: None } (134 to 139)
+47: FlagParam { long: NodeId(44), short: Some(NodeId(46)), ty: None, custom_completion: None, default: None } (134 to 139)
 48: Name (145 to 146) "x"
-49: PosParam { name: NodeId(48), ty: None, default: None } (145 to 146)
+49: PosParam { name: NodeId(48), ty: None, custom_completion: None, default: None, is_optional: false } (145 to 146)
 50: Name (148 to 149) "y"
 51: Name (151 to 154) "int"
 52: Type { name: NodeId(51), args: None, optional: false } (151 to 154)
-53: PosParam { name: NodeId(50), ty: Some(NodeId(52)), default: None } (148 to 154)
+53: PosParam { name: NodeId(50), ty: Some(NodeId(52)), custom_completion: None, default: None, is_optional: false } (148 to 154)
 54: Params(ParamsId(2)) (117 to 155)
 55: Variable (159 to 163) "$bar"
 56: Variable (165 to 169) "$baz"
@@ -66,14 +66,76 @@ input_file: tests/def.nu
 59: List(ListId(1)) (158 to 177)
 60: Block(BlockId(1)) (156 to 180)
 61: Def { name: NodeId(36), type_params: None, params: NodeId(54), in_out_types: None, block: NodeId(60), env: false, wrapped: false } (99 to 180)
-62: Block(BlockId(2)) (0 to 181)
+62: Name (213 to 223) "completion"
+63: Params(ParamsId(3)) (224 to 226)
+64: Int (230 to 231) "1"
+65: Int (233 to 234) "2"
+66: Int (236 to 237) "3"
+67: List(ListId(2)) (229 to 237)
+68: Block(BlockId(2)) (227 to 240)
+69: Def { name: NodeId(62), type_params: None, params: NodeId(63), in_out_types: None, block: NodeId(68), env: false, wrapped: false } (209 to 240)
+70: Name (245 to 264) "foo-with-completion"
+71: Name (268 to 271) "bar"
+72: FlagLong(NodeId(71)) (266 to 271)
+73: Name (273 to 276) "int"
+74: Type { name: NodeId(73), args: None, optional: false } (273 to 276)
+75: Name (277 to 287) "completion"
+76: FlagParam { long: NodeId(72), short: None, ty: Some(NodeId(74)), custom_completion: Some(NodeId(75)), default: None } (266 to 276)
+77: Name (289 to 292) "baz"
+78: Name (294 to 297) "int"
+79: Type { name: NodeId(78), args: None, optional: false } (294 to 297)
+80: Name (298 to 308) "completion"
+81: PosParam { name: NodeId(77), ty: Some(NodeId(79)), custom_completion: Some(NodeId(80)), default: None, is_optional: false } (289 to 297)
+82: Params(ParamsId(4)) (265 to 309)
+83: Variable (313 to 317) "$bar"
+84: Variable (319 to 323) "$baz"
+85: List(ListId(3)) (312 to 323)
+86: Block(BlockId(3)) (310 to 326)
+87: Def { name: NodeId(70), type_params: None, params: NodeId(82), in_out_types: None, block: NodeId(86), env: false, wrapped: false } (241 to 326)
+88: Name (332 to 344) "foo-optional"
+89: Name (346 to 347) "x"
+90: Name (349 to 352) "int"
+91: Type { name: NodeId(90), args: None, optional: false } (349 to 352)
+92: PosParam { name: NodeId(89), ty: Some(NodeId(91)), custom_completion: None, default: None, is_optional: false } (346 to 352)
+93: Name (354 to 355) "y"
+94: Name (358 to 361) "int"
+95: Type { name: NodeId(94), args: None, optional: false } (358 to 361)
+96: PosParam { name: NodeId(93), ty: Some(NodeId(95)), custom_completion: None, default: None, is_optional: true } (354 to 361)
+97: Params(ParamsId(5)) (345 to 362)
+98: Variable (366 to 368) "$x"
+99: Variable (370 to 372) "$y"
+100: List(ListId(4)) (365 to 372)
+101: Block(BlockId(4)) (363 to 375)
+102: Def { name: NodeId(88), type_params: None, params: NodeId(97), in_out_types: None, block: NodeId(101), env: false, wrapped: false } (328 to 375)
+103: Name (380 to 388) "foo-rest"
+104: Name (390 to 391) "x"
+105: Name (393 to 396) "int"
+106: Type { name: NodeId(105), args: None, optional: false } (393 to 396)
+107: PosParam { name: NodeId(104), ty: Some(NodeId(106)), custom_completion: None, default: None, is_optional: false } (390 to 396)
+108: Name (401 to 402) "y"
+109: RestParam { name: NodeId(108), ty: None, custom_completion: None } (401 to 402)
+110: Params(ParamsId(6)) (389 to 403)
+111: Variable (407 to 409) "$x"
+112: Variable (411 to 413) "$y"
+113: List(ListId(5)) (406 to 413)
+114: Block(BlockId(5)) (404 to 416)
+115: Def { name: NodeId(103), type_params: None, params: NodeId(110), in_out_types: None, block: NodeId(114), env: false, wrapped: false } (376 to 416)
+116: Block(BlockId(6)) (0 to 417)
 ==== SCOPE ====
-0: Frame Scope, node_id: NodeId(62)
-      decls: [ foo-with-flag: NodeId(36), foo: NodeId(0) ]
+0: Frame Scope, node_id: NodeId(116)
+      decls: [ completion: NodeId(62), foo-optional: NodeId(88), foo-rest: NodeId(103), foo-with-completion: NodeId(70), foo-with-flag: NodeId(36), foo: NodeId(0) ]
 1: Frame Scope, node_id: NodeId(34)
   variables: [ w: NodeId(1), x: NodeId(3), y: NodeId(7), z: NodeId(17) ]
 2: Frame Scope, node_id: NodeId(60)
   variables: [ --bar: NodeId(38), --baz: NodeId(44), x: NodeId(48), y: NodeId(50) ]
+3: Frame Scope, node_id: NodeId(68) (empty)
+4: Frame Scope, node_id: NodeId(86)
+  variables: [ --bar: NodeId(72), baz: NodeId(77) ]
+5: Frame Scope, node_id: NodeId(101)
+  variables: [ x: NodeId(89), y: NodeId(93) ]
+6: Frame Scope, node_id: NodeId(114)
+  variables: [ x: NodeId(104), y: NodeId(108) ]
 ==== SCOPE ERRORS ====
 Error (NodeId 55): variable `bar` not found
 Error (NodeId 56): variable `baz` not found
+Error (NodeId 83): variable `bar` not found
diff --git a/src/snapshots/new_nu_parser__test__node_output@extern.nu.snap b/src/snapshots/new_nu_parser__test__node_output@extern.nu.snap
index 2e8add0..c9d74b0 100644
--- a/src/snapshots/new_nu_parser__test__node_output@extern.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@extern.nu.snap
@@ -8,7 +8,7 @@ input_file: tests/extern.nu
 1: Name (13 to 17) "text"
 2: Name (19 to 25) "string"
 3: Type { name: NodeId(2), args: None, optional: false } (19 to 25)
-4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), default: None } (13 to 25)
+4: PosParam { name: NodeId(1), ty: Some(NodeId(3)), custom_completion: None, default: None, is_optional: false } (13 to 25)
 5: Params(ParamsId(0)) (12 to 26)
 6: Extern { name: NodeId(0), params: NodeId(5) } (0 to 26)
 7: Block(BlockId(0)) (0 to 27)
diff --git a/src/snapshots/new_nu_parser__test__node_output@infer_complex.nu.snap b/src/snapshots/new_nu_parser__test__node_output@infer_complex.nu.snap
index 1c76b0f..8118357 100644
--- a/src/snapshots/new_nu_parser__test__node_output@infer_complex.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@infer_complex.nu.snap
@@ -13,27 +13,27 @@ input_file: tests/infer_complex.nu
 6: Name (24 to 25) "a"
 7: Name (27 to 28) "A"
 8: Type { name: NodeId(7), args: None, optional: false } (27 to 28)
-9: PosParam { name: NodeId(6), ty: Some(NodeId(8)), default: None } (24 to 28)
+9: PosParam { name: NodeId(6), ty: Some(NodeId(8)), custom_completion: None, default: None, is_optional: false } (24 to 28)
 10: Name (30 to 31) "b"
 11: Name (33 to 34) "B"
 12: Type { name: NodeId(11), args: None, optional: false } (33 to 34)
-13: PosParam { name: NodeId(10), ty: Some(NodeId(12)), default: None } (30 to 34)
+13: PosParam { name: NodeId(10), ty: Some(NodeId(12)), custom_completion: None, default: None, is_optional: false } (30 to 34)
 14: Params(ParamsId(1)) (23 to 35)
 15: RecordType { fields: NodeId(14), optional: false } (17 to 35)
-16: PosParam { name: NodeId(4), ty: Some(NodeId(15)), default: None } (14 to 35)
+16: PosParam { name: NodeId(4), ty: Some(NodeId(15)), custom_completion: None, default: None, is_optional: false } (14 to 35)
 17: Name (37 to 38) "y"
 18: Name (40 to 46) "record"
 19: Name (47 to 48) "a"
 20: Name (50 to 51) "A"
 21: Type { name: NodeId(20), args: None, optional: false } (50 to 51)
-22: PosParam { name: NodeId(19), ty: Some(NodeId(21)), default: None } (47 to 51)
+22: PosParam { name: NodeId(19), ty: Some(NodeId(21)), custom_completion: None, default: None, is_optional: false } (47 to 51)
 23: Name (53 to 54) "b"
 24: Name (56 to 57) "B"
 25: Type { name: NodeId(24), args: None, optional: false } (56 to 57)
-26: PosParam { name: NodeId(23), ty: Some(NodeId(25)), default: None } (53 to 57)
+26: PosParam { name: NodeId(23), ty: Some(NodeId(25)), custom_completion: None, default: None, is_optional: false } (53 to 57)
 27: Params(ParamsId(2)) (46 to 58)
 28: RecordType { fields: NodeId(27), optional: false } (40 to 59)
-29: PosParam { name: NodeId(17), ty: Some(NodeId(28)), default: None } (37 to 59)
+29: PosParam { name: NodeId(17), ty: Some(NodeId(28)), custom_completion: None, default: None, is_optional: false } (37 to 59)
 30: Params(ParamsId(3)) (12 to 60)
 31: Name (63 to 70) "nothing"
 32: Type { name: NodeId(31), args: None, optional: false } (63 to 70)
@@ -41,11 +41,11 @@ input_file: tests/infer_complex.nu
 34: Name (81 to 82) "a"
 35: Name (84 to 85) "A"
 36: Type { name: NodeId(35), args: None, optional: false } (84 to 85)
-37: PosParam { name: NodeId(34), ty: Some(NodeId(36)), default: None } (81 to 85)
+37: PosParam { name: NodeId(34), ty: Some(NodeId(36)), custom_completion: None, default: None, is_optional: false } (81 to 85)
 38: Name (87 to 88) "b"
 39: Name (90 to 91) "B"
 40: Type { name: NodeId(39), args: None, optional: false } (90 to 91)
-41: PosParam { name: NodeId(38), ty: Some(NodeId(40)), default: None } (87 to 91)
+41: PosParam { name: NodeId(38), ty: Some(NodeId(40)), custom_completion: None, default: None, is_optional: false } (87 to 91)
 42: Params(ParamsId(4)) (80 to 92)
 43: RecordType { fields: NodeId(42), optional: false } (74 to 93)
 44: InOutType(NodeId(32), NodeId(43)) (63 to 93)
@@ -59,7 +59,7 @@ input_file: tests/infer_complex.nu
 52: Name (122 to 123) "x"
 53: Name (125 to 128) "int"
 54: Type { name: NodeId(53), args: None, optional: false } (125 to 128)
-55: PosParam { name: NodeId(52), ty: Some(NodeId(54)), default: None } (122 to 128)
+55: PosParam { name: NodeId(52), ty: Some(NodeId(54)), custom_completion: None, default: None, is_optional: false } (122 to 128)
 56: Params(ParamsId(6)) (120 to 130)
 57: Name (133 to 140) "nothing"
 58: Type { name: NodeId(57), args: None, optional: false } (133 to 140)
@@ -79,7 +79,7 @@ input_file: tests/infer_complex.nu
 72: Name (185 to 186) "a"
 73: Name (188 to 194) "number"
 74: Type { name: NodeId(73), args: None, optional: false } (188 to 194)
-75: PosParam { name: NodeId(72), ty: Some(NodeId(74)), default: None } (185 to 194)
+75: PosParam { name: NodeId(72), ty: Some(NodeId(74)), custom_completion: None, default: None, is_optional: false } (185 to 194)
 76: Params(ParamsId(7)) (184 to 195)
 77: RecordType { fields: NodeId(76), optional: false } (178 to 196)
 78: Name (198 to 199) "f"
diff --git a/src/snapshots/new_nu_parser__test__node_output@infer_generics.nu.snap b/src/snapshots/new_nu_parser__test__node_output@infer_generics.nu.snap
index 70be49e..66edcd4 100644
--- a/src/snapshots/new_nu_parser__test__node_output@infer_generics.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@infer_generics.nu.snap
@@ -10,7 +10,7 @@ input_file: tests/infer_generics.nu
 3: Name (11 to 12) "x"
 4: Name (14 to 15) "T"
 5: Type { name: NodeId(4), args: None, optional: false } (14 to 15)
-6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), default: None } (11 to 15)
+6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), custom_completion: None, default: None, is_optional: false } (11 to 15)
 7: Params(ParamsId(1)) (9 to 17)
 8: Name (20 to 27) "nothing"
 9: Type { name: NodeId(8), args: None, optional: false } (20 to 27)
diff --git a/src/snapshots/new_nu_parser__test__node_output@infer_plus.nu.snap b/src/snapshots/new_nu_parser__test__node_output@infer_plus.nu.snap
index 571b189..c2c4f2b 100644
--- a/src/snapshots/new_nu_parser__test__node_output@infer_plus.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@infer_plus.nu.snap
@@ -10,7 +10,7 @@ input_file: tests/infer_plus.nu
 3: Name (20 to 21) "x"
 4: Name (23 to 26) "int"
 5: Type { name: NodeId(4), args: None, optional: false } (23 to 26)
-6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), default: None } (20 to 26)
+6: PosParam { name: NodeId(3), ty: Some(NodeId(5)), custom_completion: None, default: None, is_optional: false } (20 to 26)
 7: Params(ParamsId(1)) (18 to 28)
 8: Name (31 to 38) "nothing"
 9: Type { name: NodeId(8), args: None, optional: false } (31 to 38)
diff --git a/src/snapshots/new_nu_parser__test__node_output@invalid_types.nu.snap b/src/snapshots/new_nu_parser__test__node_output@invalid_types.nu.snap
index 749dfe6..401a8fe 100644
--- a/src/snapshots/new_nu_parser__test__node_output@invalid_types.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@invalid_types.nu.snap
@@ -13,7 +13,7 @@ input_file: tests/invalid_types.nu
 6: Type { name: NodeId(5), args: None, optional: false } (22 to 28)
 7: TypeArgs(TypeArgsId(0)) (16 to 29)
 8: Type { name: NodeId(2), args: Some(NodeId(7)), optional: false } (12 to 16)
-9: PosParam { name: NodeId(1), ty: Some(NodeId(8)), default: None } (9 to 16)
+9: PosParam { name: NodeId(1), ty: Some(NodeId(8)), custom_completion: None, default: None, is_optional: false } (9 to 16)
 10: Params(ParamsId(0)) (8 to 30)
 11: Variable (33 to 35) "$x"
 12: Block(BlockId(0)) (31 to 37)
@@ -23,7 +23,7 @@ input_file: tests/invalid_types.nu
 16: Name (50 to 54) "list"
 17: TypeArgs(TypeArgsId(1)) (54 to 56)
 18: Type { name: NodeId(16), args: Some(NodeId(17)), optional: false } (50 to 54)
-19: PosParam { name: NodeId(15), ty: Some(NodeId(18)), default: None } (47 to 54)
+19: PosParam { name: NodeId(15), ty: Some(NodeId(18)), custom_completion: None, default: None, is_optional: false } (47 to 54)
 20: Params(ParamsId(1)) (46 to 57)
 21: Variable (60 to 62) "$y"
 22: Block(BlockId(1)) (58 to 64)
diff --git a/src/snapshots/new_nu_parser__test__node_output@let_mismatch.nu.snap b/src/snapshots/new_nu_parser__test__node_output@let_mismatch.nu.snap
index 7de8e98..2eb1b05 100644
--- a/src/snapshots/new_nu_parser__test__node_output@let_mismatch.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@let_mismatch.nu.snap
@@ -37,7 +37,7 @@ input_file: tests/let_mismatch.nu
 30: Name (138 to 139) "a"
 31: Name (141 to 144) "int"
 32: Type { name: NodeId(31), args: None, optional: false } (141 to 144)
-33: PosParam { name: NodeId(30), ty: Some(NodeId(32)), default: None } (138 to 144)
+33: PosParam { name: NodeId(30), ty: Some(NodeId(32)), custom_completion: None, default: None, is_optional: false } (138 to 144)
 34: Params(ParamsId(0)) (137 to 145)
 35: RecordType { fields: NodeId(34), optional: false } (131 to 146)
 36: String (149 to 150) "a"
diff --git a/src/snapshots/new_nu_parser__test__node_output@reparse.nu.snap b/src/snapshots/new_nu_parser__test__node_output@reparse.nu.snap
index 308e7ee..8ec903f 100644
--- a/src/snapshots/new_nu_parser__test__node_output@reparse.nu.snap
+++ b/src/snapshots/new_nu_parser__test__node_output@reparse.nu.snap
@@ -6,7 +6,7 @@ input_file: tests/reparse.nu
 ==== COMPILER ====
 0: Variable (4 to 5) "x"
 1: Name (10 to 11) "a"
-2: PosParam { name: NodeId(1), ty: None, default: None } (10 to 11)
+2: PosParam { name: NodeId(1), ty: None, custom_completion: None, default: None, is_optional: false } (10 to 11)
 3: Params(ParamsId(0)) (9 to 12)
 4: Variable (13 to 15) "$a"
 5: Block(BlockId(0)) (13 to 16)
diff --git a/src/typechecker.rs b/src/typechecker.rs
index f304978..b653bfa 100644
--- a/src/typechecker.rs
+++ b/src/typechecker.rs
@@ -259,7 +259,9 @@ impl<'a> Typechecker<'a> {
             AstNode::PosParam {
                 name,
                 ty,
+                custom_completion: _,
                 default: _,
+                is_optional: _,
             } => {
                 if let Some(ty) = ty {
                     let ty_id = self.typecheck_type(ty);
@@ -986,7 +988,9 @@ impl<'a> Typechecker<'a> {
                         let AstNode::PosParam {
                             name,
                             ty,
+                            custom_completion: _,
                             default: _,
+                            is_optional: _,
                         } = self.compiler.get_node(*field)
                         else {
                             panic!("internal error: record field isn't Param");
diff --git a/tests/def.nu b/tests/def.nu
index 3e7d9a8..522bd7f 100644
--- a/tests/def.nu
+++ b/tests/def.nu
@@ -2,3 +2,10 @@ def foo [w x: int, y: list<list<int>>, z: record<a, b: int> ] { [ $w $x, $y, $z
 
 # define flag
 def foo-with-flag [--bar: int = 3, --baz(-b), x, y: int] { [$bar, $baz, $x, $y] }
+
+# define custom completion
+def completion [] { [1, 2, 3] }
+def foo-with-completion [--bar: int@completion, baz: int@completion] { [$bar, $baz] }
+
+def foo-optional [x: int, y?: int] { [$x, $y] }
+def foo-rest [x: int, ...y] { [$x, $y] }