Fix #8523

src/server/editorServices.ts

@@ -803,6 +803,7 @@ namespace ts.server {
             else {
                 this.findReferencingProjects(info);
                 if (info.defaultProject) {
+                    info.defaultProject.addOpenRef();
                     this.openFilesReferenced.push(info);
                 }
                 else {

tests/cases/unittests/tsserverProjectSystem.ts

@@ -567,5 +567,32 @@ namespace ts {
             checkConfiguredProjectActualFiles(project, [file1.path, classicModuleFile.path]);
             checkNumberOfInferredProjects(projectService, 1);
         });
+
+        it("should keep the configured project when the opened file is referenced by the project but not its root", () => {
+            const file1: FileOrFolder = {
+                path: "/a/b/main.ts",
+                content: "import { objA } from './obj-a';"
+            };
+            const file2: FileOrFolder = {
+                path: "/a/b/obj-a.ts",
+                content: `export const objA = Object.assign({foo: "bar"}, {bar: "baz"});`
+            };
+            const configFile: FileOrFolder = {
+                path: "/a/b/tsconfig.json",
+                content: `{
+                    "compilerOptions": {
+                        "target": "es6"
+                    }, 
+                    "files": [ "main.ts" ]
+                }`
+            };
+            const host = new TestServerHost(/*useCaseSensitiveFileNames*/ false, getExecutingFilePathFromLibFile(libFile), "/", [file1, file2, configFile]);
+            const projectService = new server.ProjectService(host, nullLogger);
+            projectService.openClientFile(file1.path);
+            projectService.closeClientFile(file1.path);
+            projectService.openClientFile(file2.path);
+            checkNumberOfConfiguredProjects(projectService, 1);
+            checkNumberOfInferredProjects(projectService, 0);
+        });
     });
 }