[api-extractor] Add support for "import type" imports

apps/api-extractor/src/analyzer/AstImport.ts

@@ -42,6 +42,7 @@ export interface IAstImportOptions {
   readonly importKind: AstImportKind;
   readonly modulePath: string;
   readonly exportName: string;
+  readonly isTypeOnly: boolean;
 }
 
 /**
@@ -82,6 +83,17 @@ export class AstImport {
    */
   public readonly exportName: string;
 
+  /**
+   * Whether it is a type-only import, for example:
+   *
+   * ```ts
+   * import type { X } from "y";
+   * ```
+   *
+   * This is set to true ONLY if the type-only form is used in *every* reference to this AstImport.
+   */
+  public isTypeOnlyEverywhere: boolean;
+
   /**
    * If this import statement refers to an API from an external package that is tracked by API Extractor
    * (according to `PackageMetadataManager.isAedocSupportedFor()`), then this property will return the
@@ -102,6 +114,9 @@ export class AstImport {
     this.modulePath = options.modulePath;
     this.exportName = options.exportName;
 
+    // We start with this assumption, but it may get changed later if non-type-only import is encountered.
+    this.isTypeOnlyEverywhere = options.isTypeOnly;
+
     this.key = AstImport.getKey(options);
   }
 

apps/api-extractor/src/analyzer/ExportAnalyzer.ts

@@ -444,7 +444,8 @@ export class ExportAnalyzer {
           return this._fetchAstImport(declarationSymbol, {
             importKind: AstImportKind.NamedImport,
             modulePath: externalModulePath,
-            exportName: exportName
+            exportName: exportName,
+            isTypeOnly: false
           });
         }
 
@@ -498,7 +499,8 @@ export class ExportAnalyzer {
         return this._fetchAstImport(undefined, {
           importKind: AstImportKind.StarImport,
           exportName: declarationSymbol.name,
-          modulePath: externalModulePath
+          modulePath: externalModulePath,
+          isTypeOnly: ExportAnalyzer._getIsTypeOnly(importDeclaration)
         });
       }
 
@@ -530,7 +532,8 @@ export class ExportAnalyzer {
           return this._fetchAstImport(declarationSymbol, {
             importKind: AstImportKind.NamedImport,
             modulePath: externalModulePath,
-            exportName: exportName
+            exportName: exportName,
+            isTypeOnly: ExportAnalyzer._getIsTypeOnly(importDeclaration)
           });
         }
 
@@ -563,7 +566,8 @@ export class ExportAnalyzer {
           return this._fetchAstImport(declarationSymbol, {
             importKind: AstImportKind.DefaultImport,
             modulePath: externalModulePath,
-            exportName
+            exportName,
+            isTypeOnly: ExportAnalyzer._getIsTypeOnly(importDeclaration)
           });
         }
 
@@ -604,7 +608,8 @@ export class ExportAnalyzer {
           return this._fetchAstImport(declarationSymbol, {
             importKind: AstImportKind.EqualsImport,
             modulePath: externalModuleName,
-            exportName: variableName
+            exportName: variableName,
+            isTypeOnly: false
           });
         }
       }
@@ -624,6 +629,13 @@ export class ExportAnalyzer {
     return undefined;
   }
 
+  private static _getIsTypeOnly(importDeclaration: ts.ImportDeclaration): boolean {
+    if (importDeclaration.importClause) {
+      return !!importDeclaration.importClause.isTypeOnly;
+    }
+    return false;
+  }
+
   private _getExportOfSpecifierAstModule(
     exportName: string,
     importOrExportDeclaration: ts.ImportDeclaration | ts.ExportDeclaration,
@@ -700,7 +712,8 @@ export class ExportAnalyzer {
           return this._fetchAstImport(astSymbol.followedSymbol, {
             importKind: AstImportKind.NamedImport,
             modulePath: starExportedModule.externalModulePath,
-            exportName: exportName
+            exportName: exportName,
+            isTypeOnly: false
           });
         }
 
@@ -815,6 +828,12 @@ export class ExportAnalyzer {
           addIfMissing: true
         });
       }
+    } else {
+      // If we encounter at least one import that does not use the type-only form,
+      // then the .d.ts rollup will NOT use "import type".
+      if (!options.isTypeOnly) {
+        astImport.isTypeOnlyEverywhere = false;
+      }
     }
 
     return astImport;

apps/api-extractor/src/generators/DtsEmitHelpers.ts

@@ -18,28 +18,34 @@ export class DtsEmitHelpers {
     collectorEntity: CollectorEntity,
     astImport: AstImport
   ): void {
+    const importPrefix: string = astImport.isTypeOnlyEverywhere ? 'import type' : 'import';
+
     switch (astImport.importKind) {
       case AstImportKind.DefaultImport:
         if (collectorEntity.nameForEmit !== astImport.exportName) {
-          stringWriter.write(`import { default as ${collectorEntity.nameForEmit} }`);
+          stringWriter.write(`${importPrefix} { default as ${collectorEntity.nameForEmit} }`);
         } else {
-          stringWriter.write(`import ${astImport.exportName}`);
+          stringWriter.write(`${importPrefix} ${astImport.exportName}`);
         }
         stringWriter.writeLine(` from '${astImport.modulePath}';`);
         break;
       case AstImportKind.NamedImport:
         if (collectorEntity.nameForEmit !== astImport.exportName) {
-          stringWriter.write(`import { ${astImport.exportName} as ${collectorEntity.nameForEmit} }`);
+          stringWriter.write(`${importPrefix} { ${astImport.exportName} as ${collectorEntity.nameForEmit} }`);
         } else {
-          stringWriter.write(`import { ${astImport.exportName} }`);
+          stringWriter.write(`${importPrefix} { ${astImport.exportName} }`);
         }
         stringWriter.writeLine(` from '${astImport.modulePath}';`);
         break;
       case AstImportKind.StarImport:
-        stringWriter.writeLine(`import * as ${collectorEntity.nameForEmit} from '${astImport.modulePath}';`);
+        stringWriter.writeLine(
+          `${importPrefix} * as ${collectorEntity.nameForEmit} from '${astImport.modulePath}';`
+        );
         break;
       case AstImportKind.EqualsImport:
-        stringWriter.writeLine(`import ${collectorEntity.nameForEmit} = require('${astImport.modulePath}');`);
+        stringWriter.writeLine(
+          `${importPrefix} ${collectorEntity.nameForEmit} = require('${astImport.modulePath}');`
+        );
         break;
       default:
         throw new InternalError('Unimplemented AstImportKind');

build-tests/api-extractor-scenarios/config/build-config.json

@@ -23,6 +23,7 @@
     "exportStar3",
     "functionOverload",
     "importEquals",
+    "importType",
     "inconsistentReleaseTags",
     "internationalCharacters",
     "preapproved",

build-tests/api-extractor-scenarios/etc/test-outputs/importType/api-extractor-scenarios.api.json

@@ -0,0 +1,108 @@
+{
+  "metadata": {
+    "toolPackage": "@microsoft/api-extractor",
+    "toolVersion": "[test mode]",
+    "schemaVersion": 1003,
+    "oldestForwardsCompatibleVersion": 1001
+  },
+  "kind": "Package",
+  "canonicalReference": "api-extractor-scenarios!",
+  "docComment": "",
+  "name": "api-extractor-scenarios",
+  "members": [
+    {
+      "kind": "EntryPoint",
+      "canonicalReference": "api-extractor-scenarios!",
+      "name": "",
+      "members": [
+        {
+          "kind": "Interface",
+          "canonicalReference": "api-extractor-scenarios!A:interface",
+          "docComment": "/**\n * @public\n */\n",
+          "excerptTokens": [
+            {
+              "kind": "Content",
+              "text": "export interface A extends "
+            },
+            {
+              "kind": "Reference",
+              "text": "Lib1Class",
+              "canonicalReference": "api-extractor-lib1-test!Lib1Class:class"
+            },
+            {
+              "kind": "Content",
+              "text": " "
+            }
+          ],
+          "releaseTag": "Public",
+          "name": "A",
+          "members": [],
+          "extendsTokenRanges": [
+            {
+              "startIndex": 1,
+              "endIndex": 3
+            }
+          ]
+        },
+        {
+          "kind": "Interface",
+          "canonicalReference": "api-extractor-scenarios!B:interface",
+          "docComment": "/**\n * @public\n */\n",
+          "excerptTokens": [
+            {
+              "kind": "Content",
+              "text": "export interface B extends "
+            },
+            {
+              "kind": "Reference",
+              "text": "Lib1Interface",
+              "canonicalReference": "api-extractor-lib1-test!Lib1Interface:interface"
+            },
+            {
+              "kind": "Content",
+              "text": " "
+            }
+          ],
+          "releaseTag": "Public",
+          "name": "B",
+          "members": [],
+          "extendsTokenRanges": [
+            {
+              "startIndex": 1,
+              "endIndex": 3
+            }
+          ]
+        },
+        {
+          "kind": "Interface",
+          "canonicalReference": "api-extractor-scenarios!C:interface",
+          "docComment": "/**\n * @public\n */\n",
+          "excerptTokens": [
+            {
+              "kind": "Content",
+              "text": "export interface C extends "
+            },
+            {
+              "kind": "Reference",
+              "text": "Renamed",
+              "canonicalReference": "api-extractor-lib1-test!Lib1Interface:interface"
+            },
+            {
+              "kind": "Content",
+              "text": " "
+            }
+          ],
+          "releaseTag": "Public",
+          "name": "C",
+          "members": [],
+          "extendsTokenRanges": [
+            {
+              "startIndex": 1,
+              "endIndex": 3
+            }
+          ]
+        }
+      ]
+    }
+  ]
+}

build-tests/api-extractor-scenarios/etc/test-outputs/importType/api-extractor-scenarios.api.md

@@ -0,0 +1,25 @@
+## API Report File for "api-extractor-scenarios"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+
+import type { Lib1Class } from 'api-extractor-lib1-test';
+import { Lib1Interface } from 'api-extractor-lib1-test';
+
+// @public (undocumented)
+export interface A extends Lib1Class {
+}
+
+// @public (undocumented)
+export interface B extends Lib1Interface {
+}
+
+// @public (undocumented)
+export interface C extends Lib1Interface {
+}
+
+
+// (No @packageDocumentation comment for this package)
+
+```

build-tests/api-extractor-scenarios/etc/test-outputs/importType/rollup.d.ts

@@ -0,0 +1,16 @@
+import type { Lib1Class } from 'api-extractor-lib1-test';
+import { Lib1Interface } from 'api-extractor-lib1-test';
+
+/** @public */
+export declare interface A extends Lib1Class {
+}
+
+/** @public */
+export declare interface B extends Lib1Interface {
+}
+
+/** @public */
+export declare interface C extends Lib1Interface {
+}
+
+export { }

build-tests/api-extractor-scenarios/src/importType/index.ts

@@ -0,0 +1,16 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
+// See LICENSE in the project root for license information.
+
+import type { Lib1Class, Lib1Interface } from 'api-extractor-lib1-test';
+
+// This should prevent Lib1Interface from being emitted as a type-only import, even though B uses it that way.
+import { Lib1Interface as Renamed } from 'api-extractor-lib1-test';
+
+/** @public */
+export interface A extends Lib1Class {}
+
+/** @public */
+export interface B extends Lib1Interface {}
+
+/** @public */
+export interface C extends Renamed {}

common/changes/@microsoft/api-extractor/octogonz-import-type_2020-07-03-04-05.json

@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@microsoft/api-extractor",
+      "comment": "Add support for \"import type\" imports (new in TypeScript 3.8)",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@microsoft/api-extractor",
+  "email": "4673363+octogonz@users.noreply.github.com"
+}