Support path completions inside node_modules (#19692)

* Support path completions inside node_modules

* Fix: Start searching from current file's directory, not host.getCurrentDirectory()

* Add test for nested node_modules

* Also test in /src/folder/b.ts

src/services/pathCompletions.ts

@@ -144,8 +144,8 @@ namespace ts.Completions.PathCompletions {
 
         let result: CompletionEntry[];
 
+        const fileExtensions = getSupportedExtensions(compilerOptions);
         if (baseUrl) {
-            const fileExtensions = getSupportedExtensions(compilerOptions);
             const projectDir = compilerOptions.project || host.getCurrentDirectory();
             const absolute = isRootedDiskPath(baseUrl) ? baseUrl : combinePaths(projectDir, baseUrl);
             result = getCompletionEntriesForDirectoryFragment(fragment, normalizePath(absolute), fileExtensions, /*includeExtensions*/ false, span, host);
@@ -176,6 +176,15 @@ namespace ts.Completions.PathCompletions {
             result = [];
         }
 
+        if (compilerOptions.moduleResolution === ts.ModuleResolutionKind.NodeJs) {
+            forEachAncestorDirectory(scriptPath, ancestor => {
+                const nodeModules = combinePaths(ancestor, "node_modules");
+                if (host.directoryExists(nodeModules)) {
+                    getCompletionEntriesForDirectoryFragment(fragment, nodeModules, fileExtensions, /*includeExtensions*/ false, span, host, /*exclude*/ undefined, result);
+                }
+            });
+        }
+
         getCompletionEntriesFromTypings(host, compilerOptions, scriptPath, span, result);
 
         for (const moduleName of enumeratePotentialNonRelativeModules(fragment, scriptPath, compilerOptions, typeChecker, host)) {

tests/cases/fourslash/completionsPaths.ts

@@ -0,0 +1,21 @@
+/// <reference path="fourslash.ts" />
+
+// @moduleResolution: node
+
+// @Filename: /node_modules/x/foo.d.ts
+////not read
+
+// @Filename: /node_modules/x/bar.d.ts
+////not read
+
+// @Filename: /src/node_modules/y/index.d.ts
+////not read
+
+// @Filename: /src/a.ts
+////import {} from "/*1*/";
+
+// @Filename: /src/folder/b.ts
+////import {} from "x//*2*/";
+
+verify.completionsAt("1", ["y", "x"]);
+verify.completionsAt("2", ["bar", "foo"]);