Add package to library component in package.yaml

[fendor]

Closes #1230.

Adds some unit-tests.

Todo:

• Code tidy up
• More tests

[lukel97]

Other than the hieCommand thing this LGTM!

[fendor]

It seems that the tests fail for cabal files and ghc versions below 8.4.*.
They probably have always failed, but the additional tests have shown their failure.
What is the preferred course of action? Disabling the feature altogether? I could also try to fix it for the old ghc-versions.

[lukel97]

@fendor did the FunctionalCodeActionsSpec tests for "add package suggestions" not used to pass on 8.2.x? I presume if #1249 is happening this won't matter, too much, but out of curiosity how were they failing?

[fendor]

The problem can acutally be shown in the Unit-tests.
Given the cabal file and task to add the package text:

Example .cabal:

name:                add-package-test
version:             0.1.0.0
license:             BSD3
author:              Luke Lau
maintainer:          luke_lau@icloud.com
build-type:          Simple
extra-source-files:  ChangeLog.md
cabal-version:       >=1.10

executable AddPackage
  exposed-modules:     ./.
  main-is:             AddPackage.hs
  build-depends:       base >=4.7 && <5
  default-language:    Haskell2010

Normally the result should be:

              List
                [ TextEdit (Range (Position 0 0) (Position 7 27)) $ T.concat
                  [ "cabal-version: >=1.10\n"
                  , "name: add-package-test\n"
                  , "version: 0.1.0.0\n"
                  , "license: BSD3\n"
                  , "maintainer: [email protected]\n"
                  , "author: Luke Lau\n"
                  , "build-type: Simple\n"
                  , "extra-source-files:\n"
                  , "    ChangeLog.md"
                  ]
                , TextEdit (Range (Position 10 0) (Position 13 34)) $ T.concat
                  [ "    main-is: AddPackage.hs\n"
                  , "    default-language: Haskell2010\n"
                  , "    build-depends:\n"
                  , "        base >=4.7 && <5,\n"
                  , "        text -any"
                  ]
                ]

But on GHC 8.2.* the output is actually:

              List -- TODO: this seems to indicate that the command does nothing
                [ TextEdit (Range (Position 0 0) (Position 7 27)) $ T.concat
                  [ "name: add-package-test\n"
                  , "version: 0.1.0.0\n"
                  , "cabal-version: >=1.10\n"
                  , "build-type: Simple\n"
                  , "license: BSD3\n"
                  , "maintainer: [email protected]\n"
                  , "author: Luke Lau\n"
                  , "extra-source-files:\n"
                  , "    ChangeLog.md"
                  ]
                , TextEdit (Range (Position 9 0) (Position 13 34)) $ T.concat
                  [ "executable  AddPackage\n"
                  , "    main-is: AddPackage.hs\n"
                  ]
                ]

It seems like the build-depends field has either been swallowed, or hadnt been updated.

[fendor]

I think, we can actually merge this. It adds a bunch of useful tests and the problem this PR uncovered is present anyway. At least, it will be documented via tests now.

[alanz]

@fendor Please update this branch to work with current master, and we can merge it again.