Add Unused Import analyzer rule

[jpsim]

No description provided.

[jpsim]

Removed SwiftLint's own unused imports using this rule in #2382.

[SwiftLintBot]

	12 Messages
📖	Linting Aerial with this PR took 0.42s vs 0.38s on master (10% slower)
📖	Linting Alamofire with this PR took 3.38s vs 3.08s on master (9% slower)
📖	Linting Firefox with this PR took 13.69s vs 11.92s on master (14% slower)
📖	Linting Kickstarter with this PR took 21.04s vs 17.43s on master (20% slower)
📖	Linting Moya with this PR took 2.29s vs 1.9s on master (20% slower)
📖	Linting Nimble with this PR took 2.2s vs 1.7s on master (29% slower)
📖	Linting Quick with this PR took 0.58s vs 0.52s on master (11% slower)
📖	Linting Realm with this PR took 3.79s vs 3.13s on master (21% slower)
📖	Linting SourceKitten with this PR took 1.22s vs 1.03s on master (18% slower)
📖	Linting Sourcery with this PR took 5.27s vs 4.48s on master (17% slower)
📖	Linting Swift with this PR took 32.68s vs 28.42s on master (14% slower)
📖	Linting WordPress with this PR took 19.72s vs 16.66s on master (18% slower)

Generated by 🚫 Danger

[marcelofabri]

what do you think about making this a Set?

[codecov-io]

Codecov Report

Merging #2381 into master will decrease coverage by 0.01%.
The diff coverage is 85.91%.

@@            Coverage Diff             @@
##           master    #2381      +/-   ##
==========================================
- Coverage   90.51%   90.49%   -0.02%     
==========================================
  Files         313      314       +1     
  Lines       15704    15775      +71     
==========================================
+ Hits        14214    14276      +62     
- Misses       1490     1499       +9

Impacted Files	Coverage Δ
...tFrameworkTests/AutomaticRuleTests.generated.swift	100% <100%> (ø)	⬆️
...iftLintFramework/Rules/Lint/UnusedImportRule.swift	85.5% <85.5%> (ø)
Source/SwiftLintFramework/Models/Command.swift	98.7% <0%> (+1.29%)	⬆️

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[marcelofabri]

@jpsim Have you tried running this rule against Lyft's iOS app? I've run it against one app and gave some false positives - I think they're all related to importing a framework that imports other ones.

For example, one class was importing Photos to use AVCaptureDevice. That import was removed and the file doesn't compile anymore. Other examples are importing Firebase (instead of the specific Firebase framework).

[jpsim]

Thats expected. If you import UIKit but only use CGPoint, a more appropriate import would be CoreGraphics for example.

However, there are times when autocorrect will cause the file to no longer compile, because the wider import wasn’t replaced by a more specific one.