Support returning options from functions

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to MiniJinja are documented here.
 
+## 1.0.17
+
+- Added support for `Option<Into<Value>>` as return value from
+  functions.  #452
+
 ## 1.0.16
 
 - Tolerate underscores in number literals.  #443

minijinja/src/value/argtypes.rs

@@ -982,6 +982,15 @@ impl From<usize> for Value {
     }
 }
 
+impl<I: Into<Value>> From<Option<I>> for Value {
+    fn from(value: Option<I>) -> Self {
+        match value {
+            Some(value) => value.into(),
+            None => Value::from(()),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

minijinja/tests/test_templates.rs

@@ -8,8 +8,9 @@ use std::collections::BTreeMap;
 use std::fmt::Write;
 use std::{env, fs};
 
+use insta::assert_snapshot;
 use minijinja::value::{StructObject, Value};
-use minijinja::{context, Environment, Error, State};
+use minijinja::{context, render, Environment, Error, State};
 
 use similar_asserts::assert_eq;
 
@@ -522,3 +523,19 @@ fn test_render_to_write_state() {
     assert_eq!(state.lookup("foo"), Some(Value::from(42)));
     assert_eq!(state.call_macro("bar", &[]).ok().as_deref(), Some("x"));
 }
+
+#[test]
+fn test_functions() {
+    assert_snapshot!(
+        render!("{{ f() }}", f => Value::from_function(|| -> i32 { 42 })),
+        @"42"
+    );
+    assert_snapshot!(
+        render!("{{ f() }}", f => Value::from_function(|| -> Option<i32> { None })),
+        @"none"
+    );
+    assert_snapshot!(
+        render!("{{ f() }}", f => Value::from_function(|| -> Result<i32, Error> { Ok(23) })),
+        @"23"
+    );
+}