Error with forceConsistentCasingInFileNames when using extended config files on case insensitive systems

[netarc]

TypeScript Version: 2.7.0-dev.20171112

On case-insensitive systems, projects with forceConsistentCasingInFileNames enabled through an extended config seem to cause include conflicts when a path contains upper-case letters.

Seems to be the exact same (closed) issue as #16875

Code

tsc                             # works
tsc -p tsconfig.json            # works
tsc -p tsconfig.extended.json   # error

where tsconfig.extended.json is only the following:

{
  "extends": "./tsconfig.json"
}

with "forceConsistentCasingInFileNames": true is set in tsconfig.json

Expected behavior:
No errors to be produced.

Actual behavior:

error TS1149: File name '/Users/username/path/to/app/src/index.ts' differs from already included file name '/users/username/path/to/app/src/index.ts' only in casing.
error TS1149: File name '/Users/username/path/to/app/node_modules/@types/some-lib/index.d.ts' differs from already included file name '/users/username/path/to/app/node_modules/@types/some-lib/index.d.ts' only in casing.

Note: The original case /Users/... conflicting with a forced downcase /users/...

[weswigham]

@netarc Do you have a compact repro for this? I can't actually seem to make a simple one using just the info you've given here. (The structure of your source files may matter, for example)

[netarc]

Thanks for looking into this, I will try to add a compact repro for this when I have a moment.

[mhegazy]

closing for now. please reopen when you have more information.

[univerio]

Here's a test case:

diff --git src/harness/unittests/tsserverProjectSystem.ts src/harness/unittests/tsserverProjectSystem.ts
index 68fbc1ecba..b8f43c4641 100644
--- src/harness/unittests/tsserverProjectSystem.ts
+++ src/harness/unittests/tsserverProjectSystem.ts
@@ -6584,4 +6584,48 @@ namespace ts.projectSystem {
             checkProjectActualFiles(project, [file.path]);
         });
     });
+
+    describe("forceConsistentCasingInFileNames", () => {
+        it("works when extends is specified with a case insensitive file system", () => {
+            const rootPath = "/Users/username/dev/project";
+            const file1: FileOrFolder = {
+                path: `${rootPath}/index.ts`,
+                content: 'import {x} from "file2";',
+            };
+            const file2: FileOrFolder = {
+                path: `${rootPath}/file2.js`,
+                content: "",
+            };
+            const file2Dts: FileOrFolder = {
+                path: `${rootPath}/types/file2/index.d.ts`,
+                content: "export declare const x: string;",
+            };
+            const tsconfigAll: FileOrFolder = {
+                path: `${rootPath}/tsconfig.all.json`,
+                content: JSON.stringify({
+                    compilerOptions: {
+                        baseUrl: ".",
+                        paths: { file2: ["./file2.js"] },
+                        typeRoots: ["./types"],
+                        forceConsistentCasingInFileNames: true,
+                    },
+                }),
+            };
+            const tsconfig: FileOrFolder = {
+                path: `${rootPath}/tsconfig.json`,
+                content: JSON.stringify({ extends: "./tsconfig.all.json" }),
+            };
+
+            const host = createServerHost([file1, file2, file2Dts, libFile, tsconfig, tsconfigAll], { useCaseSensitiveFileNames: false });
+            const session = createSession(host);
+
+            openFilesForSession([file1], session);
+            const projectService = session.getProjectService();
+
+            checkNumberOfProjects(projectService, { configuredProjects: 1 });
+
+            const diagnostics = configuredProjectAt(projectService, 0).getLanguageService().getCompilerOptionsDiagnostics();
+            assert.deepEqual(diagnostics, []);
+        });
+    });
 }

PR #20311 does seem to fix this issue.