Lowercase type reference directives when determining to reuse program structure (just like when we create new program)

src/compiler/program.ts

@@ -1178,7 +1178,8 @@ namespace ts {
                     }
                 }
                 if (resolveTypeReferenceDirectiveNamesWorker) {
-                    const typesReferenceDirectives = map(newSourceFile.typeReferenceDirectives, x => x.fileName);
+                    // We lower-case all type references because npm automatically lowercases all packages. See GH#9824.
+                    const typesReferenceDirectives = map(newSourceFile.typeReferenceDirectives, ref => ref.fileName.toLocaleLowerCase());
                     const resolutions = resolveTypeReferenceDirectiveNamesWorker(typesReferenceDirectives, newSourceFilePath);
                     // ensure that types resolutions are still correct
                     const resolutionsChanged = hasChangesInResolutions(typesReferenceDirectives, resolutions, oldSourceFile.resolvedTypeReferenceDirectiveNames, typeDirectiveIsEqualTo);

src/testRunner/unittests/tsserverProjectSystem.ts

@@ -9555,6 +9555,65 @@ export function Test2() {
         });
     });
 
+    describe("tsserverProjectSystem typeReferenceDirectives", () => {
+        it("when typeReferenceDirective contains UpperCasePackage", () => {
+            const projectLocation = "/user/username/projects/myproject";
+            const libProjectLocation = `${projectLocation}/lib`;
+            const typeLib: File = {
+                path: `${libProjectLocation}/@types/UpperCasePackage/index.d.ts`,
+                content: `declare class BrokenTest {
+    constructor(name: string, width: number, height: number, onSelect: Function);
+    Name: string;
+    SelectedFile: string;
+}`
+            };
+            const appLib: File = {
+                path: `${libProjectLocation}/@app/lib/index.d.ts`,
+                content: `/// <reference types="UpperCasePackage" />
+declare class TestLib {
+    issue: BrokenTest;
+    constructor();
+    test(): void;
+}`
+            };
+            const testProjectLocation = `${projectLocation}/test`;
+            const testFile: File = {
+                path: `${testProjectLocation}/test.ts`,
+                content: `class TestClass1 {
+
+    constructor() {
+        var l = new TestLib();
+
+    }
+
+    public test2() {
+        var x = new BrokenTest('',0,0,null);
+
+    }
+}`
+            };
+            const testConfig: File = {
+                path: `${testProjectLocation}/tsconfig.json`,
+                content: JSON.stringify({
+                    compilerOptions: {
+                        module: "amd",
+                        typeRoots: ["../lib/@types", "../lib/@app"]
+                    }
+                })
+            };
+
+            const files = [typeLib, appLib, testFile, testConfig, libFile];
+            const host = createServerHost(files);
+            const service = createProjectService(host);
+            service.openClientFile(testFile.path);
+            checkNumberOfProjects(service, { configuredProjects: 1 });
+            const project = service.configuredProjects.get(testConfig.path)!;
+            checkProjectActualFiles(project, files.map(f => f.path));
+            host.writeFile(appLib.path, appLib.content.replace("test()", "test2()"));
+            host.checkTimeoutQueueLengthAndRun(2);
+        });
+    });
+
     describe("tsserverProjectSystem project references", () => {
         const aTs: File = {
             path: "/a/a.ts",