Improve "Cannot read .cabal file inside ..." errors

[9999years]

This error message was very confusing -- it doesn't tell you what .cabal file it's looking for or why it cannot read the .cabal file. (Did it fail to parse the .tar archive itself? Did parsing the .cabal file fail? If so, why?)

This patch improves the error message to include the name of the .cabal file being searched for. Additionally, parse errors and warnings are printed, as are format failures in the tarball itself.

I ran into this error while I was writing tests for Cabal and it confused the hell out of me; this is an expanded version of the changes I made to help debug that failure.

Before:

Error: [Cabal-7046]
Cannot read .cabal file inside my-lib-1.0.tar.gz

After:

Error: In <ROOT>/cabal.dist/repo/my-lib-1.0.tar.gz: Errors encountered when parsing cabal file my-lib-1.0/my-lib.cabal:

my-lib-1.0/my-lib.cabal:4:22: error:
unexpected Unknown SPDX license identifier: 'puppy' 

    3 | version:        1.0
    4 | license:        puppy license :)
      |                      ^

my-lib-1.0/my-lib.cabal:5:1: warning:
Unknown field: "puppy"

    4 | license:        puppy license :)
    5 | puppy:          teehee!
      | ^
Error: [Cabal-7046]
Failed to read my-lib-1.0/my-lib.cabal from archive <ROOT>/cabal.dist/repo/my-lib-1.0.tar.gz

• Tests have been added (Ask for help if you don’t know how to write them)
  • Manual QA notes have been added
• A changelog entry has been added in changelog.d/pr-YOUR_PR_NUMBER
• Documentation has been updated
• Haddock comments for new top-level definitions have been added
• base and third-party library imports use qualified imports or explicit import lists
• Commit messages are formatted nicely
• Post-merge: Backports for older Cabal release branches have been created

[geekosaur]

Can we have (a) a PR template and (b) a changelog entry, since this is user visible? Otherwise, nice.

[ulysses4ever]

Nice!

[9999years]

OK, added a changelog entry and updated the test suite. I think moving .cabal file warnings from info to warn resulted in a bunch of output being added to the cli-suite.

[jasagredo]

I am afraid I have to request changes until the comment below is taken care of. I will push a branch that implements the changes I describe, to merge into this one.

[jasagredo]

I'm sorry it seems like it needs a formatting change. Here is a patch to apply
fmt.patch

[jasagredo]

Thanks for merging the PR.

[jasagredo]

Oof we need to add file-uri to the bootstrap jobs. That is kind of easy on Linux and a nightmare on Windows, so if someone else could take care of that it would be awesome.

[jasagredo]

Aha I see those errors and they are because of file-uri not supporting uri fragments.

ghci> parseFileURI ExtendedPosix "file:/tmp/bar#shared-cache"
Left "endOfInput"
ghci> parseFileURI ExtendedPosix "file:/tmp/bar"
Right (FileURI {fileAuth = Nothing, filePath = "/tmp/bar"})

So I guess we will have to split the string? takeWhile (/= '#')?

[jasagredo]

Here is a patch I would push for this change.
frag.patch
(I can't push to your branch)

[9999years]

@jasagredo I'm going to undo your changes for now, let this get merged with the hack, and then we can see about making it cleaner in a follow-up PR.

[mergify]

This pull request has been removed from the queue for the following reason: pull request branch update failed.

The pull request can't be updated.

You should look at the reason for the failure and decide if the pull request needs to be fixed or if you want to requeue it.

If you want to requeue this pull request, you need to post a comment with the text: @mergifyio requeue

[geekosaur]

/cc: @9999years

[geekosaur]

You had the bad luck of being in the queue behind another PR, so it needs to be rebased again. It still has merge delay passed, so it should be requeued as soon as you rebase it instead of requiring another 2 day delay.