add support for importing typescript types and deduping imports

src/cli.ts

@@ -1,6 +1,7 @@
 #!/usr/bin/env node
 
 import minimist from 'minimist'
+import {cloneDeep} from 'lodash'
 import {readFileSync, writeFileSync, existsSync, lstatSync, readdirSync, mkdirSync} from 'fs'
 import {glob, isDynamicPattern} from 'tinyglobby'
 import {join, resolve, dirname} from 'path'
@@ -23,6 +24,7 @@ main(
       'strictIndexSignatures',
       'unknownAny',
       'unreachableDefinitions',
+      'useTypeImports',
     ],
     default: DEFAULT_OPTIONS,
     string: ['bannerComment', 'cwd'],
@@ -101,7 +103,11 @@ async function processDir(argIn: string, argOut: string | undefined, argv: Parti
         return [file, await processFile(file, argv)] as const
       } else {
         const outputPath = pathTransform(argOut, argIn, file)
-        return [file, await processFile(file, argv), outputPath] as const
+        // get argv with cwd corrected. We want to resolve relevant to dir.
+        const opts = cloneDeep(argv)
+        const dirPath = resolve(dirname(file))
+        opts.cwd = resolve(dirPath)
+        return [file, await processFile(file, opts), outputPath] as const
       }
     }),
   )
@@ -179,6 +185,9 @@ Boolean values can be set to false using the 'no-' prefix.
       Root directory for resolving $ref
   --declareExternallyReferenced
       Declare external schemas referenced via '$ref'?
+  --useTypeImports
+      Access external schemas referenced via '$ref' using 'import type'? This
+      requires --declareExternallyReferenced=false.
   --enableConstEnums
       Prepend enums with 'const'?
   --inferStringEnumKeysFromValues

src/generator.ts

@@ -15,6 +15,7 @@ import {
   T_UNKNOWN,
 } from './types/AST'
 import {log, toSafeString} from './utils'
+import {basename, dirname, extname, join} from 'path'
 
 export function generate(ast: AST, options = DEFAULT_OPTIONS): string {
   return (
@@ -349,14 +350,36 @@ function generateStandaloneEnum(ast: TEnum, options: Options): string {
 }
 
 function generateStandaloneInterface(ast: TNamedInterface, options: Options): string {
-  return (
-    (hasComment(ast) ? generateComment(ast.comment, ast.deprecated) + '\n' : '') +
+  const lines: string[] = []
+
+  hasComment(ast) ? lines.push(generateComment(ast.comment, ast.deprecated) + '\n') : lines.push('')
+
+  if (options.useTypeImports) {
+    for (const param of ast.params) {
+      if (param.ast.standaloneName && param.referencePath) {
+        const dir = dirname(param.referencePath)
+        const nameWithoutExt = basename(param.referencePath, extname(param.referencePath))
+        // If we needed to rename due to name clashes, import with the original
+        // name.
+        const importInBrackets =
+          param.ast.originalName && param.ast.originalName !== param.ast.standaloneName
+            ? `${param.ast.originalName} as ${param.ast.standaloneName}`
+            : param.ast.standaloneName
+        const importPath = './' + join(dir, `${nameWithoutExt}.ts`)
+        lines.push(`import type { ${importInBrackets} } from '${importPath}';`)
+      }
+    }
+  }
+
+  lines.push(
     `export interface ${toSafeString(ast.standaloneName)} ` +
-    (ast.superTypes.length > 0
-      ? `extends ${ast.superTypes.map(superType => toSafeString(superType.standaloneName)).join(', ')} `
-      : '') +
-    generateInterface(ast, options)
+      (ast.superTypes.length > 0
+        ? `extends ${ast.superTypes.map(superType => toSafeString(superType.standaloneName)).join(', ')} `
+        : '') +
+      generateInterface(ast, options),
   )
+
+  return lines.join('')
 }
 
 function generateStandaloneType(ast: ASTWithStandaloneName, options: Options): string {

src/index.ts

@@ -44,6 +44,10 @@ export interface Options {
    * Declare external schemas referenced via `$ref`?
    */
   declareExternallyReferenced: boolean
+  /**
+   * Use `import type` instead of redeclaring.
+   */
+  useTypeImports: boolean
   /**
    * Prepend enums with [`const`](https://www.typescriptlang.org/docs/handbook/enums.html#computed-and-constant-members)?
    */
@@ -98,6 +102,7 @@ export const DEFAULT_OPTIONS: Options = {
 */`,
   cwd: process.cwd(),
   declareExternallyReferenced: true,
+  useTypeImports: false,
   enableConstEnums: true,
   inferStringEnumKeysFromValues: false,
   format: true,
@@ -135,7 +140,10 @@ function parseAsJSONSchema(filename: string): JSONSchema4 {
 export async function compile(schema: JSONSchema4, name: string, options: Partial<Options> = {}): Promise<string> {
   validateOptions(options)
 
-  const _options = merge({}, DEFAULT_OPTIONS, options)
+  // useTypeImports implies declareExternallyReferenced = false
+  const optionOverrides = options.useTypeImports ? {declareExternallyReferenced: false} : {}
+
+  const _options = merge({}, DEFAULT_OPTIONS, options, optionOverrides)
 
   const start = Date.now()
   function time() {
@@ -151,6 +159,7 @@ export async function compile(schema: JSONSchema4, name: string, options: Partia
   const _schema = cloneDeep(schema)
 
   const {dereferencedPaths, dereferencedSchema} = await dereference(_schema, _options)
+
   if (process.env.VERBOSE) {
     if (isDeepStrictEqual(_schema, dereferencedSchema)) {
       log('green', 'dereferencer', time(), '✅ No change')
@@ -176,7 +185,7 @@ export async function compile(schema: JSONSchema4, name: string, options: Partia
   const normalized = normalize(linked, dereferencedPaths, name, _options)
   log('yellow', 'normalizer', time(), '✅ Result:', normalized)
 
-  const parsed = parse(normalized, _options)
+  const parsed = parse(normalized, _options, dereferencedPaths)
   log('blue', 'parser', time(), '✅ Result:', parsed)
 
   const optimized = optimize(parsed, _options)

src/normalizer.ts

@@ -99,10 +99,6 @@ rules.set('Add an $id to anything that needs it', (schema, fileName, _options, _
   if (!schema.$id && !schema.title && dereferencedName) {
     schema.$id = toSafeString(justName(dereferencedName))
   }
-
-  if (dereferencedName) {
-    dereferencedPaths.delete(schema)
-  }
 })
 
 rules.set('Escape closing JSDoc comment', schema => {