2 files changed, 98 insertions, 9 deletions

diff --git a/serde_dhall/src/options/de.rs b/serde_dhall/src/options/de.rs
index dcc6bac..4f7c346 100644
--- a/serde_dhall/src/options/de.rs
+++ b/serde_dhall/src/options/de.rs
@@ -1,5 +1,5 @@
-use std::path::{Path, PathBuf};
 use std::collections::HashMap;
+use std::path::{Path, PathBuf};
 
 use dhall::{Ctxt, Parsed};
 
@@ -228,7 +228,7 @@ impl<'a, A> Deserializer<'a, A> {
     //     self
     // }
 
-    /// Sets a Collection of names which should be substituted with
+    /// injects a collection of names which should be substituted with
     /// the given types, i.e. effectively adds built-in type variables
     /// which do not need to be imported within dhall.
     ///
@@ -258,20 +258,43 @@ impl<'a, A> Deserializer<'a, A> {
     /// let data = "Newtype.Bar";
     ///
     /// let deserialized = serde_dhall::from_str(data)
-    ///   .substitute_names(substs)
+    ///   .inject_types(substs)
     ///   .parse::<Newtype>()
     ///   .unwrap();
     ///
     /// assert_eq!(deserialized, Newtype::Bar);
     ///
     /// ```
-    pub fn substitute_names(self, substs: HashMap<String, SimpleType>) -> Self {
+    pub fn inject_types(
+        self,
+        tys: impl IntoIterator<Item = (String, SimpleType)>,
+    ) -> Self {
         Deserializer {
-            substitutions: substs
-                .iter()
+            substitutions: tys
+                .into_iter()
                 .map(|(s, ty)| {
-                    (dhall::syntax::Label::from_str(s), ty.to_expr())
+                    (dhall::syntax::Label::from_str(&s), ty.to_expr())
                 })
+                .chain(
+                    self.substitutions
+                        .iter()
+                        .map(|(n,t)| (n.clone(), t.clone())),
+                )
+                .collect(),
+            ..self
+        }
+    }
+
+    pub fn inject_single_type(self, name: String, ty: SimpleType) -> Self {
+        Deserializer {
+            substitutions: self
+                .substitutions
+                .iter()
+                .map(|(n,t)| (n.clone(),t.clone()))
+                .chain(std::iter::once((
+                    dhall::syntax::Label::from_str(&name),
+                    ty.to_expr(),
+                )))
                 .collect(),
             ..self
         }
diff --git a/serde_dhall/tests/serde.rs b/serde_dhall/tests/serde.rs
index 99e4b8b..abf78e3 100644
--- a/serde_dhall/tests/serde.rs
+++ b/serde_dhall/tests/serde.rs
@@ -151,7 +151,73 @@ mod serde {
     }
 
     #[test]
-    fn substitutions() {
+    fn inject_single_type() {
+        #[derive(Debug, Clone, Deserialize, Serialize, StaticType, Eq, PartialEq)]
+        enum Foo {
+            X(u64),
+            Y(i64),
+        }
+
+        assert_eq!(from_str("Foo.X 1")
+                   .inject_single_type("Foo".to_string(), Foo::static_type())
+                   .static_type_annotation()
+                   .parse::<Foo>()
+                   .unwrap(),
+                   Foo::X(1)
+        )
+    }
+
+    #[test]
+    fn chain_inject_type() {
+        #[derive(Debug, Clone, Deserialize, Serialize, StaticType, Eq, PartialEq)]
+        enum Bar {
+            A,B
+        }
+        #[derive(Debug, Clone, Deserialize, Serialize, StaticType, Eq, PartialEq)]
+        enum Foo {
+            X(Bar),
+            Y(i64),
+        }
+
+        assert_eq!(from_str("Foo.X Bar.A")
+                   .inject_single_type("Bar".to_string(), Bar::static_type())
+                   .inject_single_type("Foo".to_string(), Foo::static_type())
+                   .static_type_annotation()
+                   .parse::<Foo>()
+                   .unwrap(),
+                   Foo::X(Bar::A)
+        );
+
+        let mut substs = collections::HashMap::new();
+        substs.insert("Foo".to_string(), Foo::static_type());
+
+        assert_eq!(from_str("Foo.X Bar.A")
+                   .inject_types(substs.clone())
+                   .inject_single_type("Bar".to_string(), Bar::static_type())
+                   .static_type_annotation()
+                   .parse::<Foo>()
+                   .unwrap(),
+                   Foo::X(Bar::A)
+        );
+
+
+        // check that in chained injects, later injects override earlier ones
+        substs.insert("Bar".to_string(), Foo::static_type());
+
+        assert_eq!(from_str("Foo.X Bar.A")
+                   .inject_types(substs)
+                   .inject_single_type("Bar".to_string(), Bar::static_type())
+                   .static_type_annotation()
+                   .parse::<Foo>()
+                   .unwrap(),
+                   Foo::X(Bar::A)
+        );
+
+
+
+    }
+    #[test]
+    fn inject_types() {
         #[derive(Debug, Clone, Deserialize, Serialize, StaticType, Eq, PartialEq)]
         enum Foo {
             X(u64),
@@ -162,7 +228,7 @@ mod serde {
         substs.insert("Foo".to_string(), Foo::static_type());
 
         assert_eq!(from_str("Foo.X 1")
-                   .substitute_names(substs)
+                   .inject_types(substs)
                    .static_type_annotation()
                    .parse::<Foo>()
                    .unwrap(),