fix: Treat a repeated override file path in a different case as a repeat on Windows

packages/shared/sdk-server/__tests__/overrides/createOverrideSource.test.ts

@@ -14,6 +14,15 @@ function makeContext(logger: LDLogger, withFilesystem: boolean = true): ClientCo
   });
 }
 
+function makeContextOn(logger: LDLogger, osName: string): ClientContext {
+  const platform = createBasicPlatform();
+  platform.info.platformData.mockReturnValue({ os: { name: osName } });
+  return new ClientContext('sdk-key', new Configuration({ logger }), {
+    ...platform,
+    fileSystem: new MockFilesystem(),
+  });
+}
+
 describe('given a client context with filesystem support', () => {
   let logger: MockLogger;
   let context: ClientContext;
@@ -161,6 +170,28 @@ describe('given a client context with filesystem support', () => {
     expect(logger.warn).toHaveBeenCalledWith(expect.stringContaining('more than once'));
   });
 
+  it('drops a path repeated in a different case on Windows, where file names ignore case', () => {
+    const windowsLogger = makeMockLogger();
+    const source = createOverrideSource(
+      { type: 'file', paths: ['C:\\overrides\\a.json', 'c:\\Overrides\\A.JSON'] },
+      makeContextOn(windowsLogger, 'Windows'),
+    ) as FileOverrideSource;
+
+    expect(source.config.paths).toEqual(['C:\\overrides\\a.json']);
+    expect(windowsLogger.warn).toHaveBeenCalledWith(expect.stringContaining('more than once'));
+  });
+
+  it('keeps paths that differ only in case on other platforms', () => {
+    const linuxLogger = makeMockLogger();
+    const source = createOverrideSource(
+      { type: 'file', paths: ['/overrides/a.json', '/Overrides/A.json'] },
+      makeContextOn(linuxLogger, 'Linux'),
+    ) as FileOverrideSource;
+
+    expect(source.config.paths).toEqual(['/overrides/a.json', '/Overrides/A.json']);
+    expect(linuxLogger.warn).not.toHaveBeenCalled();
+  });
+
   it('fails construction for a YAML file when no parser is configured', () => {
     // The SDK does not include a YAML parser, so such a file could never load. That is a
     // configuration error, reported once at construction rather than on every reload.

packages/shared/sdk-server/src/overrides/createOverrideSource.ts

@@ -45,8 +45,18 @@ function validateFileOverrideSourceOptions(
     throw new Error('The file-based override source requires at least one file path');
   }
   // A path listed more than once would make every entry of that file a duplicate of itself, so
-  // the repeats are dropped and the first occurrence keeps its place in the order.
-  const paths = options.paths.filter((path, index) => options.paths.indexOf(path) === index);
+  // the repeats are dropped and the first occurrence keeps its place in the order. Windows file
+  // names ignore case, so there a path repeated in a different case names the same file.
+  const ignoreCase = clientContext.platform.info.platformData().os?.name === 'Windows';
+  const seen = new Set<string>();
+  const paths = options.paths.filter((path) => {
+    const comparable = ignoreCase ? path.toLowerCase() : path;
+    if (seen.has(comparable)) {
+      return false;
+    }
+    seen.add(comparable);
+    return true;
+  });
   if (paths.length !== options.paths.length) {
     logger?.warn(
       'dataSystem.overrides.paths lists the same file more than once; the repeats are ignored',