Fix #15540: Throw error when importing @types (#15866)

* Fix #15540: Throw error when importing @types

Fix issue: #15540

- Modify checker; external imports to account for imported modules
containing '@types/'.
- Add diagnostic message.
- Add test case

* FIX-15540: Review changes

- Replace `substr` with `startsWith`
- move diagnostics message to more relevant place
- Add `removePrefix` helper function

src/compiler/checker.ts

@@ -1642,6 +1642,12 @@ namespace ts {
                 return;
             }
 
+            if (startsWith(moduleReference, "@types/")) {
+                const diag = Diagnostics.Cannot_import_type_declaration_files_Consider_importing_0_instead_of_1;
+                const withoutAtTypePrefix = removePrefix(moduleReference, "@types/");
+                error(errorNode, diag, withoutAtTypePrefix, moduleReference);
+            }
+
             const ambientModule = tryFindAmbientModule(moduleName, /*withAugmentations*/ true);
             if (ambientModule) {
                 return ambientModule;

src/compiler/core.ts

@@ -1764,6 +1764,11 @@ namespace ts {
         return str.lastIndexOf(prefix, 0) === 0;
     }
 
+    /* @internal */
+    export function removePrefix(str: string, prefix: string): string {
+        return startsWith(str, prefix) ? str.substr(prefix.length) : str;
+    }
+
     /* @internal */
     export function endsWith(str: string, suffix: string): boolean {
         const expectedPos = str.length - suffix.length;

src/compiler/diagnosticMessages.json

@@ -3061,6 +3061,10 @@
         "category": "Message",
         "code": 6136
     },
+    "Cannot import type declaration files. Consider importing '{0}' instead of '{1}'.": {
+        "category": "Error",
+        "code": 6137
+    },
     "Property '{0}' is declared but never used.": {
         "category": "Error",
         "code": 6138

tests/baselines/reference/importDeclTypes.errors.txt

@@ -0,0 +1,14 @@
+tests/cases/compiler/a.ts(1,21): error TS6137: Cannot import type declaration files. Consider importing 'foo-bar' instead of '@types/foo-bar'.
+
+
+==== /node_modules/@types/foo-bar/index.d.ts (0 errors) ====
+    export interface Foo {
+        bar: string;
+    }
+    
+    // This should error
+==== tests/cases/compiler/a.ts (1 errors) ====
+    import { Foo } from "@types/foo-bar";
+                        ~~~~~~~~~~~~~~~~
+!!! error TS6137: Cannot import type declaration files. Consider importing 'foo-bar' instead of '@types/foo-bar'.
+    

tests/baselines/reference/importDeclTypes.js

@@ -0,0 +1,15 @@
+//// [tests/cases/compiler/importDeclTypes.ts] ////
+
+//// [index.d.ts]
+export interface Foo {
+    bar: string;
+}
+
+// This should error
+//// [a.ts]
+import { Foo } from "@types/foo-bar";
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;

tests/cases/compiler/importDeclTypes.ts

@@ -0,0 +1,9 @@
+
+// @filename: /node_modules/@types/foo-bar/index.d.ts
+export interface Foo {
+    bar: string;
+}
+
+// This should error
+// @filename: a.ts
+import { Foo } from "@types/foo-bar";