From caf73c36f2456b4d08e6319b88b83891cb59e03e Mon Sep 17 00:00:00 2001
From: JT <547158+jntrnr@users.noreply.github.com>
Date: Mon, 20 Dec 2021 17:58:09 +1100
Subject: [PATCH] Finish adding support for optional params (#530)

---
 crates/nu-engine/src/eval.rs | 22 ++++++++++++++--------
 src/tests.rs                 |  8 ++++++++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/crates/nu-engine/src/eval.rs b/crates/nu-engine/src/eval.rs
index 9498bb299b..2c08151b4f 100644
--- a/crates/nu-engine/src/eval.rs
+++ b/crates/nu-engine/src/eval.rs
@@ -39,18 +39,24 @@ fn eval_call(
         let block = engine_state.get_block(block_id);
 
         let mut stack = stack.collect_captures(&block.captures);
-        for (arg, param) in call.positional.iter().zip(
-            decl.signature()
-                .required_positional
-                .iter()
-                .chain(decl.signature().optional_positional.iter()),
-        ) {
-            let result = eval_expression(engine_state, &mut stack, arg)?;
+
+        for (param_idx, param) in decl
+            .signature()
+            .required_positional
+            .iter()
+            .chain(decl.signature().optional_positional.iter())
+            .enumerate()
+        {
             let var_id = param
                 .var_id
                 .expect("internal error: all custom parameters must have var_ids");
 
-            stack.add_var(var_id, result);
+            if let Some(arg) = call.positional.get(param_idx) {
+                let result = eval_expression(engine_state, &mut stack, arg)?;
+                stack.add_var(var_id, result);
+            } else {
+                stack.add_var(var_id, Value::nothing(call.head));
+            }
         }
 
         if let Some(rest_positional) = decl.signature().rest_positional {
diff --git a/src/tests.rs b/src/tests.rs
index bb2f28bae8..61f2fdfac0 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1300,3 +1300,11 @@ fn get_table_columns_1() -> TestResult {
 fn get_table_columns_2() -> TestResult {
     run_test("[[name, age, grade]; [paul,21,a]] | columns | nth 1", "age")
 }
+
+#[test]
+fn allow_missing_optional_params() -> TestResult {
+    run_test(
+        "def foo [x?:int] { if $x != $nothing { $x + 10 } else { 5 } }; foo",
+        "5",
+    )
+}