feat(interface-types) Introduce the record type.

This patch updates the `Type` type to be an enum with 2 variants:
`Function` and `Record`, resp. to represent:

1. `(@interface type (func (param i32 i32) (result string)))`
2. `(@interface type (record string i32))`

This patch updates the binary encoder and decoder, along with the WAT
encoder and decoder.

src/ast.rs

@@ -50,18 +50,41 @@ pub enum InterfaceType {
     I64,
 }
 
-/// Represents a type signature.
-///
-/// ```wasm,ignore
-/// (@interface type (param i32 i32) (result string))
-/// ```
+/// Represents the kind of type.
 #[derive(PartialEq, Debug)]
-pub struct Type {
-    /// Types for the parameters (`(param …)`).
-    pub inputs: Vec<InterfaceType>,
+pub enum TypeKind {
+    /// A function type.
+    Function,
 
-    /// Types for the results (`(result …)`).
-    pub outputs: Vec<InterfaceType>,
+    /// A record type.
+    Record,
+}
+
+/// Represents a type.
+#[derive(PartialEq, Debug)]
+pub enum Type {
+    /// A function type, like:
+    ///
+    /// ```wasm,ignore
+    /// (@interface type (func (param i32 i32) (result string)))
+    /// ```
+    Function {
+        /// Types for the parameters (`(param …)`).
+        inputs: Vec<InterfaceType>,
+
+        /// Types for the results (`(result …)`).
+        outputs: Vec<InterfaceType>,
+    },
+
+    /// A record type, like:
+    ///
+    /// ```wasm,ignore
+    /// (@interface type (record string i32))
+    /// ```
+    Record {
+        /// Types representing the fields.
+        fields: Vec<InterfaceType>,
+    },
 }
 
 /// Represents an imported function.

src/decoders/binary.rs

@@ -32,6 +32,19 @@ impl TryFrom<u8> for InterfaceType {
     }
 }
 
+/// Parse a type kind.
+impl TryFrom<u8> for TypeKind {
+    type Error = &'static str;
+
+    fn try_from(code: u8) -> Result<Self, Self::Error> {
+        Ok(match code {
+            0x00 => Self::Function,
+            0x01 => Self::Record,
+            _ => return Err("Unknown type kind code."),
+        })
+    }
+}
+
 /// Parse an interface kind.
 impl TryFrom<u8> for InterfaceKind {
     type Error = &'static str;
@@ -234,10 +247,25 @@ fn types<'input, E: ParseError<&'input [u8]>>(
     let mut types = Vec::with_capacity(number_of_types as usize);
 
     for _ in 0..number_of_types {
-        consume!((input, inputs) = list(input, ty)?);
-        consume!((input, outputs) = list(input, ty)?);
+        consume!((input, type_kind) = byte(input)?);
 
-        types.push(Type { inputs, outputs });
+        let type_kind = TypeKind::try_from(type_kind)
+            .map_err(|_| Err::Error(make_error(input, ErrorKind::ParseTo)))?;
+
+        match type_kind {
+            TypeKind::Function => {
+                consume!((input, inputs) = list(input, ty)?);
+                consume!((input, outputs) = list(input, ty)?);
+
+                types.push(Type::Function { inputs, outputs });
+            }
+
+            TypeKind::Record => {
+                consume!((input, fields) = list(input, ty)?);
+
+                types.push(Type::Record { fields });
+            }
+        }
     }
 
     Ok((input, types))

src/decoders/wat.rs

@@ -13,6 +13,7 @@ mod keyword {
     // New keywords.
     custom_keyword!(implement);
     custom_keyword!(r#type = "type");
+    custom_keyword!(record);
 
     // New types.
     custom_keyword!(s8);
@@ -401,25 +402,48 @@ impl<'a> Parse<'a> for Type {
     fn parse(parser: Parser<'a>) -> Result<Self> {
         parser.parse::<keyword::r#type>()?;
 
-        let (inputs, outputs) = parser.parens(|parser| {
-            parser.parse::<keyword::func>()?;
+        let ty = parser.parens(|parser| {
+            let mut lookahead = parser.lookahead1();
 
-            let mut input_types = vec![];
-            let mut output_types = vec![];
+            if lookahead.peek::<keyword::func>() {
+                parser.parse::<keyword::func>()?;
 
-            while !parser.is_empty() {
-                let function_type = parser.parse::<FunctionType>()?;
+                let mut input_types = vec![];
+                let mut output_types = vec![];
 
-                match function_type {
-                    FunctionType::Input(mut inputs) => input_types.append(&mut inputs),
-                    FunctionType::Output(mut outputs) => output_types.append(&mut outputs),
+                while !parser.is_empty() {
+                    let function_type = parser.parse::<FunctionType>()?;
+
+                    match function_type {
+                        FunctionType::Input(mut inputs) => input_types.append(&mut inputs),
+                        FunctionType::Output(mut outputs) => output_types.append(&mut outputs),
+                    }
                 }
-            }
 
-            Ok((input_types, output_types))
+                Ok(Type::Function {
+                    inputs: input_types,
+                    outputs: output_types,
+                })
+            } else if lookahead.peek::<keyword::record>() {
+                parser.parse::<keyword::record>()?;
+
+                let fields = parser.parens(|parser| {
+                    let mut fields = vec![];
+
+                    while !parser.is_empty() {
+                        fields.push(parser.parse()?);
+                    }
+
+                    Ok(fields)
+                })?;
+
+                Ok(Type::Record { fields })
+            } else {
+                Err(lookahead.error())
+            }
         })?;
 
-        Ok(Type { inputs, outputs })
+        Ok(ty)
     }
 }
 

src/encoders/binary.rs

@@ -112,6 +112,19 @@ where
     }
 }
 
+/// Encode a `TypeKind` into bytes.
+impl<W> ToBytes<W> for TypeKind
+where
+    W: Write,
+{
+    fn to_bytes(&self, writer: &mut W) -> io::Result<()> {
+        match self {
+            TypeKind::Function => 0x00_u8.to_bytes(writer),
+            TypeKind::Record => 0x01_u8.to_bytes(writer),
+        }
+    }
+}
+
 /// Encode an `InterfaceKind` into bytes.
 impl<W> ToBytes<W> for InterfaceKind
 where
@@ -136,8 +149,18 @@ where
     W: Write,
 {
     fn to_bytes(&self, writer: &mut W) -> io::Result<()> {
-        self.inputs.to_bytes(writer)?;
-        self.outputs.to_bytes(writer)?;
+        match self {
+            Type::Function { inputs, outputs } => {
+                TypeKind::Function.to_bytes(writer)?;
+                inputs.to_bytes(writer)?;
+                outputs.to_bytes(writer)?;
+            }
+
+            Type::Record { fields } => {
+                TypeKind::Record.to_bytes(writer)?;
+                fields.to_bytes(writer)?;
+            }
+        }
 
         Ok(())
     }

src/encoders/wat.rs

@@ -167,11 +167,24 @@ fn output_types_to_result(output_types: &[InterfaceType]) -> String {
 /// Encode a `Type` into a string.
 impl<'input> ToString for &Type {
     fn to_string(&self) -> String {
-        format!(
-            r#"(@interface type (func{inputs}{outputs}))"#,
-            inputs = input_types_to_param(&self.inputs),
-            outputs = output_types_to_result(&self.outputs),
-        )
+        match self {
+            Type::Function { inputs, outputs } => format!(
+                r#"(@interface type (func{inputs}{outputs}))"#,
+                inputs = input_types_to_param(&inputs),
+                outputs = output_types_to_result(&outputs),
+            ),
+
+            Type::Record { fields } => format!(
+                r#"(@interface type (record {fields}))"#,
+                fields = fields
+                    .iter()
+                    .fold(String::new(), |mut accumulator, interface_type| {
+                        accumulator.push(' ');
+                        accumulator.push_str(&interface_type.to_string());
+                        accumulator
+                    }),
+            ),
+        }
     }
 }