feat(repl): allow using "type" command on types/interfaces

src/index.ts

@@ -348,6 +348,7 @@ export interface TsConfigOptions
 export interface TypeInfo {
   name: string;
   comment: string;
+  kind?: _ts.ScriptElementKind;
 }
 
 /**
@@ -831,8 +832,9 @@ export function create(rawOptions: CreateOptions = {}): Service {
         const info = service.getQuickInfoAtPosition(fileName, position);
         const name = ts.displayPartsToString(info ? info.displayParts : []);
         const comment = ts.displayPartsToString(info ? info.documentation : []);
+        const kind = info?.kind;
 
-        return { name, comment };
+        return { name, comment, kind };
       };
     } else {
       const sys: _ts.System & _ts.FormatDiagnosticsHost = {

src/repl.ts

@@ -8,6 +8,7 @@ import { readFileSync, statSync } from 'fs';
 import { Console } from 'console';
 import type * as tty from 'tty';
 import Module = require('module');
+import { ScriptElementKind } from 'typescript';
 
 /** @internal */
 export const EVAL_FILENAME = `[eval].ts`;
@@ -306,14 +307,37 @@ function startRepl(
       }
 
       const undo = appendEval(state, identifier);
-      const { name, comment } = service.getTypeInfo(
+      let { name, comment, kind } = service.getTypeInfo(
         state.input,
         state.path,
         state.input.length
       );
 
       undo();
 
+      // Check if the user intended to query a Type/Interface
+      if (kind === '') {
+        // Workaround to get type information
+        const undo = appendEval(state, `undefined as unknown as ${identifier}`);
+        const getTypeInfoRes = service.getTypeInfo(
+          state.input,
+          state.path,
+          state.input.length
+        );
+
+        undo();
+
+        if (
+          [
+            ScriptElementKind.typeElement,
+            ScriptElementKind.interfaceElement,
+          ].includes(getTypeInfoRes.kind!)
+        ) {
+          name = getTypeInfoRes.name;
+          comment = getTypeInfoRes.comment;
+        }
+      }
+
       if (name) repl.outputStream.write(`${name}\n`);
       if (comment) repl.outputStream.write(`${comment}\n`);
       repl.displayPrompt();

src/test/index.spec.ts

@@ -401,6 +401,7 @@ test.suite('ts-node', (test) => {
       expect(stdout).to.equal('> 123\n' + 'undefined\n' + '> ');
     });
 
+    // TODO: REPL shouldn't require a leading `\n` to properly work on Windows
     test('REPL has command to get type information', async () => {
       const execPromise = exec(`${cmd} --interactive`);
       execPromise.child.stdin!.end('\nconst a = 123\n.type a');
@@ -411,6 +412,36 @@ test.suite('ts-node', (test) => {
       );
     });
 
+    // TODO: Same as above
+    // TODO2: Merge with below test once #1126 is fixed
+    test('REPL "type" command can be used on types', async () => {
+      const execPromise = exec(`${cmd} --interactive`);
+      execPromise.child.stdin!.end(
+        '\n' + 'type Foo = string | { x: 1 }\n' + '.type Foo\n'
+      );
+      const { err, stdout } = await execPromise;
+      expect(err).to.equal(null);
+      expect(stdout).to.equal(
+        '> undefined\n' +
+          '> undefined\n' +
+          '> type Foo = string | {\n    x: 1;\n}\n' +
+          '> '
+      );
+    });
+
+    // TODO: Same as above
+    test('REPL "type" command can be used on interfaces', async () => {
+      const execPromise = exec(`${cmd} --interactive`);
+      execPromise.child.stdin!.end(
+        '\n' + 'interface Bar { x: string; y: number; }\n' + '.type Bar'
+      );
+      const { err, stdout } = await execPromise;
+      expect(err).to.equal(null);
+      expect(stdout).to.equal(
+        '> undefined\n' + '> undefined\n' + '> interface Bar\n' + '> '
+      );
+    });
+
     function createReplViaApi() {
       const stdin = new PassThrough();
       const stdout = new PassThrough();
@@ -1654,6 +1685,7 @@ test.suite('ts-node', (test) => {
           service.getTypeInfo('/**jsdoc here*/const x = 10', 'test.ts', 21)
         ).to.deep.equal({
           comment: 'jsdoc here',
+          kind: 'const',
           name: 'const x: 10',
         });
       });
@@ -1664,6 +1696,7 @@ test.suite('ts-node', (test) => {
           service.getTypeInfo('/**jsdoc here*/const x = 10', 'test.ts', 0)
         ).to.deep.equal({
           comment: '',
+          kind: undefined,
           name: '',
         });
       });