Define function types

- Use `contains` object mapping style for `parameters` types and
  `returns` types. Force `parameters` to be a type wrapper around a
  tuple type (and allow `returns` to be a tuple type)

- Define one-of required fields `internal: true` xor `external: true`.

- Override external types `contains` field to also allow a `contract`
  field (for the contract in which an external function type is defined)

schemas/type/complex.schema.yaml

@@ -48,6 +48,13 @@ allOf:
     then:
       $ref: "schema:ethdebug/format/type/complex/struct"
 
+  - if:
+      properties:
+        kind:
+          const: function
+    then:
+      $ref: "schema:ethdebug/format/type/complex/function"
+
 $defs:
   Kind:
     title: Known complex kind
@@ -61,4 +68,4 @@ $defs:
       - array
       - mapping
       - struct
-
+      - function

schemas/type/complex/function.schema.yaml

@@ -0,0 +1,164 @@
+$schema: "https://json-schema.org/draft/2020-12/schema"
+$id: "schema:ethdebug/format/type/complex/function"
+
+title: ethdebug/format/type/complex/function
+description: |
+  Schema for representing a function type.
+
+  Type representations must indicate whether they represent a function that is
+  called internally (within the semantics of the language) or a function that
+  is called externally (via EVM contract call semantics and the Solidity ABI).
+  Internal function types require the `"internal": true` field; external
+  function types require `"external": true`.
+
+  Note that external function types may include a representation of the
+  contract type that defines or provides this function as an external
+  interface.
+
+type: object
+properties:
+  class:
+    type: string
+    const: complex
+  kind:
+    type: string
+    const: function
+  contains:
+    type: object
+    title: Parameter and return types
+    description: |
+      Types this function type composes. Function types inherently compose
+      two groupings of types (an ordered list of parameter types and typically
+      either a return value or return parameters). Function types' `contains`
+      field is organized as a mapping of `parameters` types (a type wrapper for
+      a tuple type) and an optional `returns` type (either a generic type
+      wrapper or a type wrapper for a tuple type).
+
+      This definition applies for both cases (internal and external function
+      types). Each of those specific types may expand this `contains` field
+      schema with other semantic details (such as an external function type
+      indicating the contract type from which it is exposed).
+    properties:
+      parameters:
+        $ref: "#/$defs/Parameters"
+      returns:
+        type: object
+        title: Return type (or tuple of types)
+        description: |
+          To accommodate languages differing in whether functions return single
+          values or lists of values, this field may be either a generic type
+          wrapper or explicitly defined as a type wrapper around a tuple type.
+
+          Debuggers that implement this schema **should** be aware that
+          languages whose functions return sole values might return tuple
+          types. Resolving this ambiguity remains outside the scope of the
+          schema (but compilers **must** be consistent when representing
+          function types in this schema).
+        anyOf:
+          - $ref: "schema:ethdebug/format/type/wrapper"
+          - $ref: "#/$defs/Parameters"
+    required:
+      - parameters
+  definition:
+    $ref: "schema:ethdebug/format/type/definition"
+
+oneOf:
+  - type: object
+    title: External function type
+    properties:
+      internal:
+        const: false
+      external:
+        const: true
+      contains:
+        type: object
+        title: Additional contents
+        properties:
+          contract:
+            type: object
+            title: Contract type providing external function
+            description:
+              A wrapper around the contract type that composes this external
+              function type.
+            allOf:
+              - $ref: "schema:ethdebug/format/type/wrapper"
+              - type: object
+                title: Contract type wrapper
+                properties:
+                  type:
+                    $ref: "schema:ethdebug/format/type/elementary/contract"
+    required:
+      - external
+
+  - type: object
+    title: Internal function type
+    properties:
+      internal:
+        const: true
+      external:
+        const: false
+    required:
+      - internal
+
+examples:
+  - kind: function
+    internal: true
+    definition:
+      name: increment
+    contains:
+      parameters:
+        type:
+          kind: tuple
+          contains:
+            - name: value
+              type:
+                kind: uint
+                bits: 256
+      returns:
+        type:
+          kind: uint
+          bits: 256
+  - kind: function
+    external: true
+    definition:
+      name: withdraw
+    contains:
+      contract:
+        type:
+          kind: contract
+          payable: true
+          interface: true
+          definition:
+            name: Bank
+      parameters:
+        type:
+          kind: tuple
+          contains:
+            - name: beneficiary
+              type:
+                kind: address
+                payable: true
+            - name: amount
+              type:
+                kind: ufixed
+                bits: 128
+                places: 18
+      returns:
+        type:
+          kind: tuple
+          contains: []
+
+$defs:
+  Parameters:
+    type: object
+    title: Parameters
+    description:
+      A type wrapper around a tuple of types. This schema uses a tuple type to
+      represent an ordered list of types.
+    allOf:
+      - $ref: "schema:ethdebug/format/type/wrapper"
+      - title: Tuple type wrapper
+        type: object
+        properties:
+          type:
+            $ref: "schema:ethdebug/format/type/complex/tuple"

tests/src/schemas.ts

@@ -32,6 +32,7 @@ const readSchemas = (): {
     "type/complex/array.schema.yaml",
     "type/complex/mapping.schema.yaml",
     "type/complex/struct.schema.yaml",
+    "type/complex/function.schema.yaml",
     "type/complex.schema.yaml",
     "type.schema.yaml",
   ];
@@ -132,6 +133,9 @@ export const schemaExtensions: {
   "schema:ethdebug/format/type/complex/struct": {
     extends: new Set(["schema:ethdebug/format/type/complex"])
   },
+  "schema:ethdebug/format/type/complex/function": {
+    extends: new Set(["schema:ethdebug/format/type/complex"])
+  },
 }
 
 const schemas = readSchemas();

web/spec/type/complex/function.mdx

@@ -0,0 +1,20 @@
+---
+sidebar_position: 6
+description: Function types schema
+---
+
+import SchemaViewer from "@site/src/components/SchemaViewer";
+
+# `function`
+
+<SchemaViewer
+  schema={{ id: "schema:ethdebug/format/type/complex/function" }}
+  />
+
+
+## Parameters schema
+
+<SchemaViewer
+  schema={{ id: "schema:ethdebug/format/type/complex/function" }}
+  pointer="#/$defs/Parameters"
+  />

web/src/schemas.ts

@@ -20,6 +20,7 @@ import typeComplexArraySchemaYaml from "../../schemas/type/complex/array.schema.
 import typeComplexMappingSchemaYaml from "../../schemas/type/complex/mapping.schema.yaml";
 import typeComplexStructSchemaYaml from "../../schemas/type/complex/struct.schema.yaml";
 import typeComplexTupleSchemaYaml from "../../schemas/type/complex/tuple.schema.yaml";
+import typeComplexFunctionSchemaYaml from "../../schemas/type/complex/function.schema.yaml";
 import typeComplexSchemaYaml from "../../schemas/type/complex.schema.yaml";
 import typeSchemaYaml from "../../schemas/type.schema.yaml";
 
@@ -44,6 +45,7 @@ export const schemaYamls = [
   typeComplexMappingSchemaYaml,
   typeComplexStructSchemaYaml,
   typeComplexTupleSchemaYaml,
+  typeComplexFunctionSchemaYaml,
   typeComplexSchemaYaml,
   typeSchemaYaml,
 ].map(schema => ({
@@ -100,14 +102,19 @@ export const schemaIndex: SchemaIndex = {
   ),
   ...(
     [
-      "alias", "tuple", "array", "mapping", "struct"
+      "alias", "tuple", "array", "mapping", "struct", "function"
     ].map(kind => ({
       [`schema:ethdebug/format/type/complex/${kind}`]: {
         href: `/spec/type/complex/${kind}`
       }
     }))
     .reduce((a, b) => ({ ...a, ...b }), {})
-  )
+  ),
+
+  "schema:ethdebug/format/type/complex/function#/$defs/Parameters": {
+    title: "Parameters schema",
+    href: "/spec/type/complex/function#parameters-schema"
+  },