3 files changed, 316 insertions, 24 deletions

diff --git a/serde_dhall/src/lib.rs b/serde_dhall/src/lib.rs
new file mode 100644
index 0000000..19aabec
--- /dev/null
+++ b/serde_dhall/src/lib.rs
@@ -0,0 +1,301 @@
+#![feature(non_exhaustive)]
+
+//! [Dhall][dhall] is a programmable configuration language that provides a non-repetitive
+//! alternative to JSON and YAML.
+//!
+//! You can think of Dhall as: JSON + types + imports + functions
+//!
+//! For a description of the Dhall language, examples, tutorials, and more, see the [language
+//! website][dhall].
+//!
+//! This crate provides support for consuming Dhall files the same way you would consume JSON or
+//! YAML. It uses the [Serde][serde] serialization library to provide drop-in support for Dhall
+//! for any datatype that supports serde (and that's a lot of them !).
+//!
+//! This library is limited to deserializing (reading) Dhall values; serializing (writing)
+//! values to Dhall is not supported for now.
+//!
+//! # Examples
+//!
+//! ### Custom datatype
+//!
+//! If you have a custom datatype for which you derived [serde::Deserialize], chances are
+//! you will be able to derive [StaticType] for it as well.
+//! This allows easy type-safe deserializing.
+//!
+//! ```edition2018
+//! use serde::Deserialize;
+//! use serde_dhall::{de::Error, StaticType};
+//!
+//! #[derive(Debug, Deserialize, StaticType)]
+//! struct Point {
+//!     x: u64,
+//!     y: u64,
+//! }
+//!
+//! fn main() -> Result<(), Error> {
+//!     // Some Dhall data
+//!     let data = "{ x = 1, y = 1 + 1 }";
+//!
+//!     // Convert the Dhall string to a Point.
+//!     let point: Point = serde_dhall::from_str_auto_type(data)?;
+//!     assert_eq!(point.x, 1);
+//!     assert_eq!(point.y, 2);
+//!
+//!     // Invalid data fails the type validation
+//!     let invalid_data = "{ x = 1, z = 0.3 }";
+//!     assert!(serde_dhall::from_str_auto_type::<Point>(invalid_data).is_err());
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ### Loosely typed
+//!
+//! If you used to consume JSON or YAML in a loosely typed way, you can continue to do so
+//! with Dhall. You only need to replace [serde_json::from_str] or [serde_yaml::from_str]
+//! with [serde_dhall::from_str][from_str].
+//! More generally, if the [StaticType] derive doesn't suit your
+//! needs, you can still deserialize any valid Dhall file that serde can handle.
+//!
+//! [serde_json::from_str]: https://docs.serde.rs/serde_json/de/fn.from_str.html
+//! [serde_yaml::from_str]: https://docs.serde.rs/serde_yaml/fn.from_str.html
+//!
+//! ```edition2018
+//! # fn main() -> serde_dhall::de::Result<()> {
+//! use std::collections::BTreeMap;
+//!
+//! // Some Dhall data
+//! let data = "{ x = 1, y = 1 + 1 } : { x: Natural, y: Natural }";
+//!
+//! // Deserialize it to a Rust type.
+//! let deserialized_map: BTreeMap<String, usize> = serde_dhall::from_str(data)?;
+//!
+//! let mut expected_map = BTreeMap::new();
+//! expected_map.insert("x".to_string(), 1);
+//! expected_map.insert("y".to_string(), 2);
+//!
+//! assert_eq!(deserialized_map, expected_map);
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! You can alternatively specify a Dhall type that the input should match.
+//!
+//! ```edition2018
+//! # fn main() -> serde_dhall::de::Result<()> {
+//! use std::collections::BTreeMap;
+//!
+//! // Parse a Dhall type
+//! let point_type_str = "{ x: Natural, y: Natural }";
+//! let point_type = serde_dhall::from_str(point_type_str)?;
+//!
+//! // Some Dhall data
+//! let point_data = "{ x = 1, y = 1 + 1 }";
+//!
+//! // Deserialize the data to a Rust type. This ensures that
+//! // the data matches the point type.
+//! let deserialized_map: BTreeMap<String, usize> =
+//!         serde_dhall::from_str_check_type(point_data, &point_type)?;
+//!
+//! let mut expected_map = BTreeMap::new();
+//! expected_map.insert("x".to_string(), 1);
+//! expected_map.insert("y".to_string(), 2);
+//!
+//! assert_eq!(deserialized_map, expected_map);
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! [dhall]: https://dhall-lang.org/
+//! [serde]: https://docs.serde.rs/serde/
+//! [serde::Deserialize]: https://docs.serde.rs/serde/trait.Deserialize.html
+
+mod serde;
+mod static_type;
+
+#[doc(inline)]
+pub use de::{from_str, from_str_auto_type, from_str_check_type};
+#[doc(hidden)]
+pub use dhall_proc_macros::StaticType;
+pub use static_type::StaticType;
+#[doc(inline)]
+pub use value::Value;
+
+// A Dhall value.
+pub mod value {
+    use dhall::core::thunk::{Thunk, TypeThunk};
+    use dhall::core::value::Value as DhallValue;
+    use dhall::phase::{NormalizedSubExpr, Parsed, Type, Typed};
+    use dhall_syntax::Builtin;
+
+    use super::de::{Error, Result};
+
+    /// A Dhall value
+    #[derive(Debug, Clone, PartialEq, Eq)]
+    pub struct Value(Typed);
+
+    impl Value {
+        pub fn from_str(s: &str, ty: Option<&Value>) -> Result<Self> {
+            Value::from_str_using_dhall_error_type(s, ty).map_err(Error::Dhall)
+        }
+        fn from_str_using_dhall_error_type(
+            s: &str,
+            ty: Option<&Value>,
+        ) -> dhall::error::Result<Self> {
+            let resolved = Parsed::parse_str(s)?.resolve()?;
+            let typed = match ty {
+                None => resolved.typecheck()?,
+                Some(t) => resolved.typecheck_with(&t.to_type())?,
+            };
+            Ok(Value(typed))
+        }
+        pub(crate) fn to_expr(&self) -> NormalizedSubExpr {
+            self.0.to_expr()
+        }
+        pub(crate) fn to_thunk(&self) -> Thunk {
+            self.0.to_thunk()
+        }
+        pub(crate) fn to_type(&self) -> Type {
+            self.0.to_type()
+        }
+
+        pub(crate) fn from_dhall_value(v: DhallValue) -> Self {
+            Value(Typed::from_value_untyped(v))
+        }
+        pub(crate) fn make_builtin_type(b: Builtin) -> Self {
+            Self::from_dhall_value(DhallValue::from_builtin(b))
+        }
+        pub(crate) fn make_optional_type(t: Value) -> Self {
+            Self::from_dhall_value(DhallValue::AppliedBuiltin(
+                Builtin::Optional,
+                vec![t.to_thunk()],
+            ))
+        }
+        pub(crate) fn make_list_type(t: Value) -> Self {
+            Self::from_dhall_value(DhallValue::AppliedBuiltin(
+                Builtin::List,
+                vec![t.to_thunk()],
+            ))
+        }
+        // Made public for the StaticType derive macro
+        #[doc(hidden)]
+        pub fn make_record_type(
+            kts: impl Iterator<Item = (String, Value)>,
+        ) -> Self {
+            Self::from_dhall_value(DhallValue::RecordType(
+                kts.map(|(k, t)| {
+                    (k.into(), TypeThunk::from_thunk(t.to_thunk()))
+                })
+                .collect(),
+            ))
+        }
+        #[doc(hidden)]
+        pub fn make_union_type(
+            kts: impl Iterator<Item = (String, Option<Value>)>,
+        ) -> Self {
+            Self::from_dhall_value(DhallValue::UnionType(
+                kts.map(|(k, t)| {
+                    (k.into(), t.map(|t| TypeThunk::from_thunk(t.to_thunk())))
+                })
+                .collect(),
+            ))
+        }
+    }
+
+    impl super::de::Deserialize for Value {
+        fn from_dhall(v: &Value) -> Result<Self> {
+            Ok(v.clone())
+        }
+    }
+}
+
+/// Deserialize Dhall data to a Rust data structure.
+pub mod de {
+    use super::StaticType;
+    use super::Value;
+    pub use error::{Error, Result};
+
+    mod error {
+        use dhall::error::Error as DhallError;
+
+        pub type Result<T> = std::result::Result<T, Error>;
+
+        #[derive(Debug)]
+        #[non_exhaustive]
+        pub enum Error {
+            Dhall(DhallError),
+            Deserialize(String),
+        }
+
+        impl std::fmt::Display for Error {
+            fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+                match self {
+                    Error::Dhall(err) => write!(f, "{}", err),
+                    Error::Deserialize(err) => write!(f, "{}", err),
+                }
+            }
+        }
+
+        impl std::error::Error for Error {}
+
+        impl serde::de::Error for Error {
+            fn custom<T>(msg: T) -> Self
+            where
+                T: std::fmt::Display,
+            {
+                Error::Deserialize(msg.to_string())
+            }
+        }
+    }
+
+    /// A data structure that can be deserialized from a Dhall expression
+    ///
+    /// This is automatically implemented for any type that [serde][serde]
+    /// can deserialize.
+    ///
+    /// This trait cannot be implemented manually.
+    // TODO: seal trait
+    pub trait Deserialize: Sized {
+        /// See [serde_dhall::from_str][crate::from_str]
+        fn from_dhall(v: &Value) -> Result<Self>;
+    }
+
+    /// Deserialize an instance of type `T` from a string of Dhall text.
+    ///
+    /// This will recursively resolve all imports in the expression, and
+    /// typecheck it before deserialization. Relative imports will be resolved relative to the
+    /// provided file. More control over this process is not yet available
+    /// but will be in a coming version of this crate.
+    pub fn from_str<T>(s: &str) -> Result<T>
+    where
+        T: Deserialize,
+    {
+        T::from_dhall(&Value::from_str(s, None)?)
+    }
+
+    /// Deserialize an instance of type `T` from a string of Dhall text,
+    /// additionally checking that it matches the supplied type.
+    ///
+    /// Like [from_str], but this additionally checks that
+    /// the type of the provided expression matches the supplied type.
+    pub fn from_str_check_type<T>(s: &str, ty: &Value) -> Result<T>
+    where
+        T: Deserialize,
+    {
+        T::from_dhall(&Value::from_str(s, Some(ty))?)
+    }
+
+    /// Deserialize an instance of type `T` from a string of Dhall text,
+    /// additionally checking that it matches the type of `T`.
+    ///
+    /// Like [from_str], but this additionally checks that
+    /// the type of the provided expression matches the output type `T`. The [StaticType] trait
+    /// captures Rust types that are valid Dhall types.
+    pub fn from_str_auto_type<T>(s: &str) -> Result<T>
+    where
+        T: Deserialize + StaticType,
+    {
+        from_str_check_type(s, &<T as StaticType>::static_type())
+    }
+}
diff --git a/dhall/src/api/serde.rs b/serde_dhall/src/serde.rs
index e1c8eef..10d5a17 100644
--- a/dhall/src/api/serde.rs
+++ b/serde_dhall/src/serde.rs
@@ -1,5 +1,5 @@
-use crate::api::de::{Deserialize, Value};
-use crate::error::{Error, Result};
+use crate::de::{Deserialize, Error, Result};
+use crate::Value;
 use dhall_syntax::{ExprF, SubExpr, X};
 use std::borrow::Cow;
 
@@ -14,15 +14,6 @@ where
 
 struct Deserializer<'a>(Cow<'a, SubExpr<X, X>>);
 
-impl serde::de::Error for Error {
-    fn custom<T>(msg: T) -> Self
-    where
-        T: std::fmt::Display,
-    {
-        Error::Deserialize(msg.to_string())
-    }
-}
-
 impl<'de: 'a, 'a> serde::de::IntoDeserializer<'de, Error> for Deserializer<'a> {
     type Deserializer = Deserializer<'a>;
     fn into_deserializer(self) -> Self::Deserializer {
diff --git a/dhall/src/api/static_type.rs b/serde_dhall/src/static_type.rs
index 906bcef..67a7bc4 100644
--- a/dhall/src/api/static_type.rs
+++ b/serde_dhall/src/static_type.rs
@@ -1,6 +1,6 @@
 use dhall_syntax::{Builtin, Integer, Natural};
 
-use crate::api::Type;
+use crate::Value;
 
 /// A Rust type that can be represented as a Dhall type.
 ///
@@ -14,14 +14,14 @@ use crate::api::Type;
 /// [StaticType] because each different value would
 /// have a different Dhall record type.
 pub trait StaticType {
-    fn static_type() -> Type;
+    fn static_type() -> Value;
 }
 
 macro_rules! derive_builtin {
     ($ty:ty, $builtin:ident) => {
         impl StaticType for $ty {
-            fn static_type() -> Type {
-                Type::make_builtin_type(Builtin::$builtin)
+            fn static_type() -> Value {
+                Value::make_builtin_type(Builtin::$builtin)
             }
         }
     };
@@ -38,8 +38,8 @@ where
     A: StaticType,
     B: StaticType,
 {
-    fn static_type() -> Type {
-        Type::make_record_type(
+    fn static_type() -> Value {
+        Value::make_record_type(
             vec![
                 ("_1".to_owned(), A::static_type()),
                 ("_2".to_owned(), B::static_type()),
@@ -54,8 +54,8 @@ where
     T: StaticType,
     E: StaticType,
 {
-    fn static_type() -> Type {
-        Type::make_union_type(
+    fn static_type() -> Value {
+        Value::make_union_type(
             vec![
                 ("Ok".to_owned(), Some(T::static_type())),
                 ("Err".to_owned(), Some(E::static_type())),
@@ -69,8 +69,8 @@ impl<T> StaticType for Option<T>
 where
     T: StaticType,
 {
-    fn static_type() -> Type {
-        Type::make_optional_type(T::static_type())
+    fn static_type() -> Value {
+        Value::make_optional_type(T::static_type())
     }
 }
 
@@ -78,8 +78,8 @@ impl<T> StaticType for Vec<T>
 where
     T: StaticType,
 {
-    fn static_type() -> Type {
-        Type::make_list_type(T::static_type())
+    fn static_type() -> Value {
+        Value::make_list_type(T::static_type())
     }
 }
 
@@ -87,7 +87,7 @@ impl<'a, T> StaticType for &'a T
 where
     T: StaticType,
 {
-    fn static_type() -> Type {
+    fn static_type() -> Value {
         T::static_type()
     }
 }