Support nullable

src/normalizer.ts

@@ -1,5 +1,5 @@
 import {JSONSchemaTypeName, LinkedJSONSchema, NormalizedJSONSchema, Parent} from './types/JSONSchema'
-import {appendToDescription, escapeBlockComment, isSchemaLike, justName, toSafeString, traverse} from './utils'
+import {appendToDescription, escapeBlockComment, isSchemaLike, justName, toSafeString, traverse, warning} from './utils'
 import {Options} from './'
 import {DereferencedPaths} from './resolver'
 import {isDeepStrictEqual} from 'util'
@@ -215,6 +215,35 @@ rules.set('Transform definitions to $defs', (schema, fileName) => {
   }
 })
 
+rules.set('Transform nullable to null type', schema => {
+  if (schema.nullable !== true) {
+    return
+  }
+
+  delete schema.nullable
+
+  if (schema.const !== undefined) {
+    if (schema.const !== null) {
+      warning('normalizer', 'const should be set to null when schema is nullable', schema)
+      schema.enum = [schema.const, null]
+      delete schema.const
+    }
+  } else if (schema.enum) {
+    if (!schema.enum.includes(null)) {
+      warning('normalizer', 'enum should include null when schema is nullable', schema)
+      schema.enum.push(null)
+    }
+  } else if (schema.type) {
+    if (Array.isArray(schema.type)) {
+      if (!schema.type.includes('null')) {
+        schema.type.push('null')
+      }
+    } else if (schema.type !== 'null') {
+      schema.type = [schema.type, 'null']
+    }
+  }
+})
+
 rules.set('Transform const to singleton enum', schema => {
   if (schema.const !== undefined) {
     schema.enum = [schema.const]

src/utils.ts

@@ -209,6 +209,13 @@ export function error(...messages: any[]): void {
   console.error(getStyledTextForLogging('red')?.('error'), ...messages)
 }
 
+export function warning(...messages: any[]): void {
+  if (!process.env.VERBOSE) {
+    return console.warn(messages)
+  }
+  console.warn(getStyledTextForLogging('yellow')?.('warning'), ...messages)
+}
+
 type LogStyle = 'blue' | 'cyan' | 'green' | 'magenta' | 'red' | 'white' | 'yellow'
 
 export function log(style: LogStyle, title: string, ...messages: unknown[]): void {

test/__snapshots__/test/test.ts.md

@@ -1883,6 +1883,33 @@ Generated by [AVA](https://avajs.dev).
     }␊
     `
 
+## nullable.js
+
+> Expected output to match snapshot for e2e test: nullable.js
+
+    `/* eslint-disable */␊
+    /**␊
+     * This file was automatically generated by json-schema-to-typescript.␊
+     * DO NOT MODIFY IT BY HAND. Instead, modify the source JSONSchema file,␊
+     * and run json-schema-to-typescript to regenerate this file.␊
+     */␊
+    ␊
+    export interface Nullable {␊
+      a?: "" | null;␊
+      b?: null;␊
+      c?: "a" | "b" | null;␊
+      d?: "" | null;␊
+      e?: string | null;␊
+      f?: null;␊
+      g?: "" | null;␊
+      h?: null;␊
+      i?: "a" | "b" | null;␊
+      j?: "" | null;␊
+      k?: string | number | null;␊
+      l?: string | null;␊
+    }␊
+    `
+
 ## oneOf.js
 
 > Expected output to match snapshot for e2e test: oneOf.js

test/e2e/nullable.ts

@@ -0,0 +1,58 @@
+export const input = {
+  type: 'object',
+  properties: {
+    a: {
+      const: '',
+      nullable: true,
+    },
+    b: {
+      const: null,
+      nullable: true,
+    },
+    c: {
+      enum: ['a', 'b'],
+      nullable: true,
+    },
+    d: {
+      enum: ['', null],
+      nullable: true,
+    },
+    e: {
+      type: 'string',
+      nullable: true,
+    },
+    f: {
+      type: 'null',
+      nullable: true,
+    },
+    g: {
+      type: 'string',
+      const: '',
+      nullable: true,
+    },
+    h: {
+      type: 'string',
+      const: null,
+      nullable: true,
+    },
+    i: {
+      type: 'string',
+      enum: ['a', 'b'],
+      nullable: true,
+    },
+    j: {
+      type: 'string',
+      enum: ['', null],
+      nullable: true,
+    },
+    k: {
+      type: ['string', 'integer'],
+      nullable: true,
+    },
+    l: {
+      type: ['string', 'null'],
+      nullable: true,
+    },
+  },
+  additionalProperties: false,
+}

test/normalizer/nullableAddsNullToType.json

@@ -0,0 +1,111 @@
+{
+  "name": "Nullable adds null to type",
+  "in": {
+    "$id": "a",
+    "type": "object",
+    "properties": {
+      "a": {
+        "const": "",
+        "nullable": true
+      },
+      "b": {
+        "const": null,
+        "nullable": true
+      },
+      "c": {
+        "enum": ["a", "b"],
+        "nullable": true
+      },
+      "d": {
+        "enum": ["", null],
+        "nullable": true
+      },
+      "e": {
+        "type": "string",
+        "nullable": true
+      },
+      "f": {
+        "type": "null",
+        "nullable": true
+      },
+      "g": {
+        "type": "string",
+        "const": "",
+        "nullable": true
+      },
+      "h": {
+        "type": "string",
+        "const": null,
+        "nullable": true
+      },
+      "i": {
+        "type": "string",
+        "enum": ["a", "b"],
+        "nullable": true
+      },
+      "j": {
+        "type": "string",
+        "enum": ["", null],
+        "nullable": true
+      },
+      "k": {
+        "type": ["string", "integer"],
+        "nullable": true
+      },
+      "l": {
+        "type": ["string", "null"],
+        "nullable": true
+      }
+    },
+    "required": [],
+    "additionalProperties": false
+  },
+  "out": {
+    "$id": "a",
+    "type": "object",
+    "properties": {
+      "a": {
+        "enum": ["", null]
+      },
+      "b": {
+        "enum": [null]
+      },
+      "c": {
+        "enum": ["a", "b", null]
+      },
+      "d": {
+        "enum": ["", null]
+      },
+      "e": {
+        "type": ["string", "null"]
+      },
+      "f": {
+        "type": "null"
+      },
+      "g": {
+        "type": "string",
+        "enum": ["", null]
+      },
+      "h": {
+        "type": "string",
+        "enum": [null]
+      },
+      "i": {
+        "type": "string",
+        "enum": ["a", "b", null]
+      },
+      "j": {
+        "type": "string",
+        "enum": ["", null]
+      },
+      "k": {
+        "type": ["string", "integer", "null"]
+      },
+      "l": {
+        "type": ["string", "null"]
+      }
+    },
+    "required": [],
+    "additionalProperties": false
+  }
+}