Spurious error: [ts] Duplicate function implementation

[garthk]

• VSCode Version: 1.5.0-insider 4fc690be310dd02e0ab6529c0b9bf348a8b26a19
• OS Version: macOS 10.11.6 (15G1004)

Steps to Reproduce:

1. vscode-insiders .
2. Edit src/big-file.ts, which is too long and stuffed with unrelated concerns
3. vscode-insiders -r src/extracted-function.ts
4. Cut a function out of src/big-file.ts
5. Paste it into src/extracted-function.ts
6. Observe red underline under the function name
7. Select it
8. Observe error: [ts] Duplicate function implementation.
9. Close src/extracted-function.ts
10. Re-open src/extracted-function.ts
11. Observe no red underline under the function name

Perhaps unrelated to #9880.

[waderyan]

This issue was moved to microsoft/TypeScript#10804