errors: diagnostic error codes link to HF error index

Closed doyougnu requested to merge doyougnu/ghc:wip/doyougnu/link-hf-error-codes into master

This MR links all error codes to the HF error Index. Given a suitable terminal a user only needs to click on the error index.

The implementation simply steals the necessary code from the GHCUP links and alters the Outputtable instance for DiagnosticCode. Any comments welcome and appreciated.

Closes: #23259 (closed)

See here for information on the escape sequence needed for terminal emulators to identify the link. I'm unsure if these escape sequences are strictly necessary as many emulators now scan for hyperlinks directly. In any case, this implementation matches that of GHCUP. Unfortunately, the escape sequences make the golden tests more ugly.

TODOs before merging:

  • CI passes
  • squash
  • Locally test the links, gitlab CI clobbers them and we'll disable for the testsuite anyhow.
  • enable flag by default
  • disable flag for testsuite
Edited by doyougnu

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