ghc-pkg package config validation too strict

Registration of a package using the following config works:

name: frob
version: 0.1.0.0
id: frob-0.1.0.0-inplace
key: frob-0.1.0.0-inplace
exposed: True
exposed-modules:
    Baz from base-4.11.1.0:Data.Bool,
    Foo from base-4.11.1.0:Data.List,
    Frob
depends:
    base-4.11.1.0

But while GHC is happy to work with the following variant of the above configuration added by hand to the package database, it's not possible to add it via ghc-pkg register, because it's rejected at validation phase:

name: frob
version: 0.1.0.0
id: frob-0.1.0.0-inplace
key: frob-0.1.0.0-inplace
exposed: True
exposed-modules:
    Baz from base:Data.Bool,
    Foo from base:Data.List,
    Frob
depends:
    base

We get the following error:

$ ghc-pkg register frob.conf
frob-0.1.0.0: module reexport refers to a non-existent defining package: base (use --force to override)

This is unfortunate, because in general unit-id's don't just have version numbers but also hashes, and in some settings these can be hard to guess.

The general point is that ghc-pkg should be exactly as permissive as GHC itself, not less or more. One way to achieve that is to make the checkModule function in utils/ghc-pkg/Main.hs (called by validatePackageConfig) use lookupPackageName as a fallback to lookupUnitId, and say that if lookupPackageName returns exactly one result (i.e. the name is unambiguous) then that should be considered okay. Perhaps not A-okay, because the name could become ambiguous in the future when more entries are added to the database, but that should at most be a warning, not an error, I think.

Note: in principle we should be able to use the --force flag here to bypass the results of configuration validation. But oddly enough, --force filters out entries that it objects about, rather than just letting them pass through. So --force is not a workable workaround.

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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CC	ezyang
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