Look at correct 'package.json' location for a scoped package (#18580)

* Look at correct 'package.json' location for a scoped package

* Update baseline

Author: Andy

src/compiler/moduleNameResolver.ts

@@ -976,18 +976,21 @@ namespace ts {
     }
 
     function loadModuleFromNodeModulesFolder(extensions: Extensions, moduleName: string, nodeModulesFolder: string, nodeModulesFolderExists: boolean, failedLookupLocations: Push<string>, state: ModuleResolutionState): Resolved | undefined {
-        const { top, rest } = getNameOfTopDirectory(moduleName);
-        const packageRootPath = combinePaths(nodeModulesFolder, top);
+        const { packageName, rest } = getPackageName(moduleName);
+        const packageRootPath = combinePaths(nodeModulesFolder, packageName);
         const { packageJsonContent, packageId } = getPackageJsonInfo(packageRootPath, rest, failedLookupLocations, !nodeModulesFolderExists, state);
         const candidate = normalizePath(combinePaths(nodeModulesFolder, moduleName));
         const pathAndExtension = loadModuleFromFile(extensions, candidate, failedLookupLocations, !nodeModulesFolderExists, state) ||
             loadNodeModuleFromDirectoryWorker(extensions, candidate, failedLookupLocations, !nodeModulesFolderExists, state, packageJsonContent);
         return withPackageId(packageId, pathAndExtension);
     }
 
-    function getNameOfTopDirectory(name: string): { top: string, rest: string } {
-        const idx = name.indexOf(directorySeparator);
-        return idx === -1 ? { top: name, rest: "" } : { top: name.slice(0, idx), rest: name.slice(idx + 1) };
+    function getPackageName(moduleName: string): { packageName: string, rest: string } {
+        let idx = moduleName.indexOf(directorySeparator);
+        if (moduleName[0] === "@") {
+            idx = moduleName.indexOf(directorySeparator, idx + 1);
+        }
+        return idx === -1 ? { packageName: moduleName, rest: "" } : { packageName: moduleName.slice(0, idx), rest: moduleName.slice(idx + 1) };
     }
 
     function loadModuleFromNodeModules(extensions: Extensions, moduleName: string, directory: string, failedLookupLocations: Push<string>, state: ModuleResolutionState, cache: NonRelativeModuleNameResolutionCache): SearchResult<Resolved> {

tests/baselines/reference/moduleResolution_packageJson_scopedPackage.js

@@ -0,0 +1,15 @@
+//// [tests/cases/compiler/moduleResolution_packageJson_scopedPackage.ts] ////
+
+//// [package.json]
+{ "types": "types.d.ts" }
+
+//// [types.d.ts]
+export const x: number;
+
+//// [a.ts]
+import { x } from "@foo/bar";
+
+
+//// [a.js]
+"use strict";
+exports.__esModule = true;

tests/baselines/reference/moduleResolution_packageJson_scopedPackage.symbols

@@ -0,0 +1,8 @@
+=== /a.ts ===
+import { x } from "@foo/bar";
+>x : Symbol(x, Decl(a.ts, 0, 8))
+
+=== /node_modules/@foo/bar/types.d.ts ===
+export const x: number;
+>x : Symbol(x, Decl(types.d.ts, 0, 12))
+

tests/baselines/reference/moduleResolution_packageJson_scopedPackage.trace.json

@@ -0,0 +1,14 @@
+[
+    "======== Resolving module '@foo/bar' from '/a.ts'. ========",
+    "Module resolution kind is not specified, using 'NodeJs'.",
+    "Loading module '@foo/bar' from 'node_modules' folder, target file type 'TypeScript'.",
+    "Found 'package.json' at '/node_modules/@foo/bar/package.json'.",
+    "File '/node_modules/@foo/bar.ts' does not exist.",
+    "File '/node_modules/@foo/bar.tsx' does not exist.",
+    "File '/node_modules/@foo/bar.d.ts' does not exist.",
+    "'package.json' does not have a 'typings' field.",
+    "'package.json' has 'types' field 'types.d.ts' that references '/node_modules/@foo/bar/types.d.ts'.",
+    "File '/node_modules/@foo/bar/types.d.ts' exist - use it as a name resolution result.",
+    "Resolving real path for '/node_modules/@foo/bar/types.d.ts', result '/node_modules/@foo/bar/types.d.ts'.",
+    "======== Module name '@foo/bar' was successfully resolved to '/node_modules/@foo/bar/types.d.ts'. ========"
+]

tests/baselines/reference/moduleResolution_packageJson_scopedPackage.types

@@ -0,0 +1,8 @@
+=== /a.ts ===
+import { x } from "@foo/bar";
+>x : number
+
+=== /node_modules/@foo/bar/types.d.ts ===
+export const x: number;
+>x : number
+

tests/baselines/reference/scopedPackages.trace.json

@@ -2,7 +2,7 @@
     "======== Resolving module '@cow/boy' from '/a.ts'. ========",
     "Module resolution kind is not specified, using 'NodeJs'.",
     "Loading module '@cow/boy' from 'node_modules' folder, target file type 'TypeScript'.",
-    "File '/node_modules/@cow/package.json' does not exist.",
+    "File '/node_modules/@cow/boy/package.json' does not exist.",
     "File '/node_modules/@cow/boy.ts' does not exist.",
     "File '/node_modules/@cow/boy.tsx' does not exist.",
     "File '/node_modules/@cow/boy.d.ts' does not exist.",

tests/cases/compiler/moduleResolution_packageJson_scopedPackage.ts

@@ -0,0 +1,11 @@
+// @noImplicitReferences: true
+// @traceResolution: true
+
+// @Filename: /node_modules/@foo/bar/package.json
+{ "types": "types.d.ts" }
+
+// @Filename: /node_modules/@foo/bar/types.d.ts
+export const x: number;
+
+// @Filename: /a.ts
+import { x } from "@foo/bar";