REPL command in project requires a target

[philderbeast]

Fixes #10527 and #9983. Depend-on: #10688.

Doesn't allow an empty list of targets with a project context.

With a project, the REPL command requires a target. If one is not given then a message is shown explaining this and naming the project if the --project-file option was given (but not when the default 'cabal.project' project name is used implicitly). We're not yet able to list project targets so in the meantime, the messages lists the packages of the project.

• When the implicit default cabal.project is used:

$ cat cabal.project
packages: pkg-one pkg-two

$ cabal repl
Error: [Cabal-7076]
With a project, the REPL command requires a single target. The packages in this
project are:
 - pkg-one
 - pkg-two

• When the --project-file option is used, the file name is included:

$ cat some.project 
packages: pkg-one pkg-two

$ cabal repl --project-file=some.project
...
Error: [Cabal-7076]
With a project, the REPL command requires a single target. The packages in this
project, 'some.project', are:
 - pkg-one
 - pkg-two

• When the project has no packages, this is mentioned in the message:

$ cat empty.project

$ cabal repl --project-file=empty.project
...
Error: [Cabal-7076]
With a project, the REPL command requires a single target but there are no
packages in this project, 'empty.project', to choose a package (library) or
other component from as the target for this command.

• Before the fix the message mentioned a fake-package-0. This was confusing:

$ ~/.ghcup/bin/cabal-3.12.1.0 repl --project-file=some.project
...
Error: [Cabal-7076]
Internal error when trying to open a repl for the package fake-package-0. The
package is not in the set of available targets for the project plan, which would
suggest an inconsistency between readTargetSelectors and resolveTargets.

• Earlier cabal-install:exe:cabal versions mentioned using all as the target but this won't work for the REPL command:

$ ~/.ghcup/bin/cabal-3.10.3.0 repl --project-file=some.project
Error: cabal-3.10.3.0: No targets given and there is no package in the current
directory. Use the target 'all' for all packages in the project or specify
packages or components by name or location. See 'cabal build --help' for more
details on target options.

---

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added.

[philderbeast]

This pull request will be easier to review once the cfgVerbosity changes are merged.

[geekosaur]

Approving despite suggestions because they're not functional changes.

[ulysses4ever]

Thanks for this patch and the test! I have a couple questions...

@mpickering could you take a brief look at this (it's a small patch)? Especially my comment under the -- NOTE:.

[ulysses4ever]

the no-packages case is certainly already handled in other places today, right? (people keep forgetting packages:... and get an error message.) Is it possible to not duplicate this logic?

[philderbeast]

After removing the target string manipulation, the current behaviour (#9983) is bad and doesn't cover this case:

$ ~/.ghcup/bin/cabal --numeric-version
3.14.2.0

$ ~/.ghcup/bin/cabal repl --project-dir=cabal-testsuite/PackageTests/ReplProjectTarget --project-file=empty.project
Configuration is affected by the following files:
- empty.project
Warning: There are no packages or optional-packages in the project
Resolving dependencies...
Error: [Cabal-7076]
Internal error when trying to open a repl for the package fake-package-0. The package is not in the set of available targets for the project plan, which would suggest an inconsistency between readTargetSelectors and resolveTargets.

Also I'd be curious to know how to get better output from a debug build of cabal-install with assertions enabled because that version gives me a poorer error report with no line number:

$ cabal repl --project-dir=cabal-testsuite/PackageTests/ReplProjectTarget --project-file=empty.project
Warning: this is a debug build of cabal-install with assertions enabled.
Configuration is affected by the following files:
- empty.project
Warning: There are no packages or optional-packages in the project
Resolving dependencies...
Assertion failed

[ulysses4ever]

Warning: There are no packages or optional-packages in the project

is a different issue, I think, (#8679 probably) so it may be wise to try to avoid solving it here.

[ulysses4ever]

assertion failure is bad but also looks like a future work. We're minutes from cutting the 3.16 branch and all backporting will have to go through extra careful consideration (mostly deciding the tradeoff: scarse resource for the release vs profit from performing the backport)

[philderbeast]

The assertion bothers me. I could cut back on the scope of this pull request or dig in more about the assertion.

[mpickering]

Did you consider modifying validatedTargets, in particular the selectPackageTargets function? That seems likely to be more correct to me than this ad-hoc manipulation of target strings.

[mpickering]

See my previous comment about modifying selectPackageTargets.

[ulysses4ever]

@philderbeast could you post a little summary on the state of this patch? Do you believe you addressed all Matt's concerns? If you're done, please ping Matt for re-reviewing.

Rebasing on master is also advisable.

There's still a chance we could get this into 3.16 but it's getting tight...

[philderbeast]

could you post a little summary on the state of this patch?

I'm currently stumbling over assertions.

[mpickering]

Let me know if you need some help with this @philderbeast