Add parser support for explicit contexts in helpers.

src/parser/parser.rs

@@ -110,6 +110,7 @@ pub struct NamedBlock<'a> {
 #[derive(Clone, Debug, PartialEq)]
 pub struct ParameterizedBlock<'a> {
     pub name: &'a str,
+    pub explicit_context: Option<Path<'a>>,
     pub params: Vec<KVPair<'a>>,
     pub contents: Option<Body<'a>>,
     pub else_contents: Option<Body<'a>>,
@@ -482,25 +483,28 @@ where
     F: Fn(ParameterizedBlock<'a>) -> DustTag<'a>,
 {
     move |i: &'a str| {
-        let (i, (name, params, inner, maybe_else, _closing_name)) = tuple((
-            preceded(tag(open_matcher), tag(tag_name)),
-            terminated(
-                opt(delimited(
-                    space1,
-                    separated_list1(space1, key_value_pair),
-                    space0,
-                )),
-                tag("}"),
-            ),
-            opt(body),
-            opt(preceded(tag("{:else}"), opt(body))),
-            delimited(tag("{/"), tag(tag_name), tag("}")),
-        ))(i)?;
+        let (i, (name, maybe_explicit_context, params, inner, maybe_else, _closing_name)) =
+            tuple((
+                preceded(tag(open_matcher), tag(tag_name)),
+                opt(preceded(tag(":"), path)),
+                terminated(
+                    opt(delimited(
+                        space1,
+                        separated_list1(space1, key_value_pair),
+                        space0,
+                    )),
+                    tag("}"),
+                ),
+                opt(body),
+                opt(preceded(tag("{:else}"), opt(body))),
+                delimited(tag("{/"), tag(tag_name), tag("}")),
+            ))(i)?;
 
         Ok((
             i,
             constructor(ParameterizedBlock {
                 name: name,
+                explicit_context: maybe_explicit_context,
                 params: params.unwrap_or(Vec::new()),
                 contents: inner,
                 else_contents: maybe_else.flatten(),
@@ -518,10 +522,11 @@ where
     F: Fn(ParameterizedBlock<'a>) -> DustTag<'a>,
 {
     move |i: &'a str| {
-        let (i, (name, params)) = delimited(
+        let (i, (name, maybe_explicit_context, params)) = delimited(
             tag(open_matcher),
             tuple((
                 tag(tag_name),
+                opt(preceded(tag(":"), path)),
                 opt(delimited(
                     space1,
                     separated_list1(space1, key_value_pair),
@@ -535,6 +540,7 @@ where
             i,
             constructor(ParameterizedBlock {
                 name: name,
+                explicit_context: maybe_explicit_context,
                 params: params.unwrap_or(Vec::new()),
                 contents: None,
                 else_contents: None,
@@ -1323,6 +1329,7 @@ mod tests {
                 "",
                 DustTag::DTHelperEquals(ParameterizedBlock {
                     name: "eq",
+                    explicit_context: None,
                     params: vec![
                         KVPair {
                             key: "key",
@@ -1359,6 +1366,74 @@ mod tests {
                 "",
                 DustTag::DTHelperEquals(ParameterizedBlock {
                     name: "eq",
+                    explicit_context: None,
+                    params: vec![
+                        KVPair {
+                            key: "key",
+                            value: RValue::RVPath(Path { keys: vec!["name"] })
+                        },
+                        KVPair {
+                            key: "value",
+                            value: RValue::RVLiteral(OwnedLiteral::LString("cat".to_owned()))
+                        }
+                    ],
+                    contents: None,
+                    else_contents: None
+                })
+            ))
+        );
+    }
+
+    #[test]
+    fn test_helper_with_explicit_context() {
+        assert_eq!(
+            dust_tag(r#"{@eq:foo.bar key=name value="cat"}Pet the {name}!{/eq}"#),
+            Ok((
+                "",
+                DustTag::DTHelperEquals(ParameterizedBlock {
+                    name: "eq",
+                    explicit_context: Some(Path {
+                        keys: vec!["foo", "bar"]
+                    }),
+                    params: vec![
+                        KVPair {
+                            key: "key",
+                            value: RValue::RVPath(Path { keys: vec!["name"] })
+                        },
+                        KVPair {
+                            key: "value",
+                            value: RValue::RVLiteral(OwnedLiteral::LString("cat".to_owned()))
+                        }
+                    ],
+                    contents: Some(Body {
+                        elements: vec![
+                            TemplateElement::TESpan(Span {
+                                contents: "Pet the "
+                            }),
+                            TemplateElement::TETag(DustTag::DTReference(Reference {
+                                path: Path { keys: vec!["name"] },
+                                filters: Vec::new()
+                            })),
+                            TemplateElement::TESpan(Span { contents: "!" })
+                        ]
+                    }),
+                    else_contents: None
+                })
+            ))
+        );
+    }
+
+    #[test]
+    fn test_self_closing_helper_with_explicit_context() {
+        assert_eq!(
+            dust_tag(r#"{@eq:foo.bar key=name value="cat"/}"#),
+            Ok((
+                "",
+                DustTag::DTHelperEquals(ParameterizedBlock {
+                    name: "eq",
+                    explicit_context: Some(Path {
+                        keys: vec!["foo", "bar"]
+                    }),
                     params: vec![
                         KVPair {
                             key: "key",