cabal-install converts the remote repo URI to a file path incorrectly on Windows.

[sebright]

This issue is item 4 from #5204, but I wanted to open a separate issue because it doesn't just affect tests.

When the url field of the repository section of the cabal config file is a file URI, cabal treats its path component as a file path, without applying a conversion:

cabal/cabal-install/Distribution/Client/GlobalFlags.hs

Lines 248 to 249 in 59bb50b

	withRepo _ callback | uriScheme remoteRepoURI == "file:" = do
	dir <- Sec.makeAbsolute $ Sec.fromFilePath (uriPath remoteRepoURI)

On Windows, the path is invalid because it contains forward slashes. If the path is an absolute path, hackage-security's path conversion code ends up removing the colon from the path and preventing cabal from reading root.json. There is more detail in #5204 (comment).

[sebright]

I tried searching for a conversion function, and the only one I could find was in haskell-lsp: https://hackage.haskell.org/package/haskell-lsp-0.2.0.1/docs/Language-Haskell-LSP-TH-DataTypesJSON.html#v:uriToFilePath