Fix/build tool depends repeats 10758

[philderbeast]

Fixes #10758.

---

• 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.

QA Notes

Use cabal init to create a package with components of your choosing and then add a build-tool-depends stanza that builds. The one from the docs is markdown-unlit:markdown-unlit >= 0.5.0 && < 0.6. When repeated, there should be a message asking that each build tool dependency is specified only once. The package should still build unless the effective intersection of version ranges is impossible to satisfy.

$ cabal build all --enable-tests --enable-benchmarks
...
Resolving dependencies...
...
As the build tool 'markdown-unlit' was specified more than once:
  - >0.5.0 && <=0.6
  - >=0 (any version)
We'll use the effective intersection of these 2 version ranges:
  - >0.5.0 && <=0.6
Please specify build tool dependencies only once.
...

[philderbeast]

I'll have to find where the solver is being called before configurePackage in Cabal/src/Distribution/Simple/Configure.hs. With the following setup that has impossible to satisfy constraints, configurePackage is not called:

...
common warnings
    ghc-options: -Wall

test-suite build-tool-depends-twice-test
    import:           warnings
    default-language: Haskell2010
    type:             exitcode-stdio-1.0
    hs-source-dirs:   test
    main-is:          Main.hs
    build-depends:    base >=4 && <5
    build-tool-depends: markdown-unlit:markdown-unlit > 0.5.0 && <= 0.6
    build-tool-depends: markdown-unlit:markdown-unlit <0

$ cabal build all --enable-tests --enable-benchmarks
...
Error: [Cabal-7107]
Could not resolve dependencies:
[__0] trying: build-tool-depends-twice-0.1.0.0 (user goal)
[__1] trying: build-tool-depends-twice:*test
[__2] next goal: build-tool-depends-twice:markdown-unlit:exe.markdown-unlit (dependency of build-tool-depends-twice *test)
[__2] rejecting: build-tool-depends-twice:markdown-unlit:exe.markdown-unlit; 0.6.0, 0.5.1, 0.5.0, 0.4.1, 0.4.0, 0.3.1, 0.2.0.1, 0.2.0, 0.1.0, 0.3.0 (conflict: build-tool-depends-twice *test => build-tool-depends-twice:markdown-unlit:exe.markdown-unlit (exe markdown-unlit)<0 && >0.5.0 && <=0.6)
[__2] fail (backjumping, conflict set: build-tool-depends-twice, build-tool-depends-twice:markdown-unlit:exe.markdown-unlit, build-tool-depends-twice:test)
After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: build-tool-depends-twice, build-tool-depends-twice:test, build-tool-depends-twice:markdown-unlit:exe.markdown-unlit

I've not seen the exe. prefix before from build-tool-depends-twice:markdown-unlit:exe.markdown-unlit. Seems odd to use . as the separator here when we use : everywhere else.

$ cabal target all:exes
...
Fully qualified target forms:
 - buildinfo-reference-generator:exe:buildinfo-reference-generator
 - cabal-install:exe:cabal
 - cabal-testsuite:exe:cabal-tests
 - cabal-testsuite:exe:setup
 - cabal-testsuite:exe:test-runtime-deps
 - cabal-validate:exe:cabal-validate
 - solver-benchmarks:exe:hackage-benchmark
Found 5 targets matching all:exes.