chore: Add buildtool plugin for SPM swiftlint support

[atierian]

Issue #, if available:
N/A

Description of changes:
Adds a buildtool() swiftlint plugin, adds that plugin as a dependency for Amplify and each plugin.
Adds // swiftlint:disable: ... in a few places in AWSCognitoAuthPlugin that were errors.

Implementation based on various points of information and examples in realm/SwiftLint#3840
This targets a specific version of swiftlint w/ checksum.

Check points: (check or cross out if not relevant)

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[atierian]

TODO

• Confirm that this change doesn't degrade customer experience pulling Amplify in as a dependency.

• Does the buildtool plugin run when a client app builds? If so, does it degrade their build time performance?

• Profile clean pull (no package cache) time. Does this change increase initial pull time?

• Do swiftlint warnings appear when a client app builds?

• Pass SWIFTPM_ENABLE_PLUGINS=1 as env variable to get tests running.

[atierian]

Clean build comparison errors and warnings.

Branch	Errors	Warnings
dev-preview (97a2bac)	0	217
chore/lint after adding swiftlint plugin	26	1246
Δ	+26	+1029

[atierian]

Clean build time comparison

Using xcodebuild -showBuildTimingSummary
building Amplify-Package, which includes Amplify + all plugins

time in seconds

Step	dev-preview	chore/lint	Δ seconds	Δ %
SwiftCompile	396.597	497.638	+101.041	+25.5
CompileC	41.800	50.452	+8.652	+20.7
SwiftEmitModule	39.986	54.112	+14.126	+35.3
SwiftDriver	24.292	22.933	-1.359	-5.6
Ld	13.807	14.642	+0.835	+6.0
GenerateDSYMFile	12.497	12.501	+0.004	+0.0
CopySwiftLibs	1.865	1.666	-0.199	-10.7
ProcessInfoPlistFile	0.947	2.540	+1.593	+168.2
Copy	0.334	0.322	-0.012	-3.6
SwiftDriver Compilation Requirements	0.277	0.368	+0.091	+32.9
WriteAuxiliaryFile	0.231	0.216	-0.015	-6.5
SwiftDriver Compilation	0.199	0.169	-0.030	-15.1
RegisterExecutionPolicyException	0.188	0.212	+0.024	+12.8
Touch	0.125	0.053	-0.072	-57.6
CpResource	0.048	0.022	-0.026	-54.2
SwiftMergeGeneratedHeaders	0.030	0.057	+0.027	+90.0
ExtractAppIntentsMetadata	0.021	0.031	+0.010	+47.6
PhaseScriptExecution	-	4.964	4.964	-

[atierian]

Client app experience

UX

After pulling in Amplify as a dependency (targeting chore/lint), the first client app build generates this popup dialog.

Not exactly the most reassuring message 😕. Selecting "Show in Issues Navigator" removes the popup and continues the build. However it appears again the next time building the client app. Selecting "Trust & Enable All" prevents the popup from appearing again, even after a clean build of the client app.

Package Resolution Time

Time in seconds from Reset Package Caches until packages are resolved.

dev-preview	chore/lint
71.3	77.4

Build Time

Current state has client apps that link Amplify running the swiftlint buildtool plugin. As if that weren't bad enough, it appears though the time to run swiftlint takes exponentially longer when building from a client app in comparison to build the Amplify package directly. This is a show stopper, so we'll have figure out a way to prevent the plugin from building when client apps build.

Action Items

• Look into ability to prevent build plugin from running when added as a dependency.

[atierian]

The linting warnings don't show up in a client app's issue navigator, but they are available in the build logs. It looks like the addition of the --cache-path speeds up subsequent builds dramatically as the linter's targeted directories aren't altered.

[atierian]

The goal of this is to add SwiftLint as a SPM buildtool plugin that runs when Amplify is built standalone (by developers working on Amplify), but never when Amplify is being built as a dependency of another target (app or library). Despite best efforts, I couldn't get that to happen. I'm throwing in the towel on this for the time being as I'm not confident that SPM plugins can accommodate this goal in their current state. Leaving the PR in draft form with all of the documented findings.

If anyone believes this is doable, I encourage you to continue work on this branch. If you have any questions about the findings listed in the comments above, feel free to ping me here.

[atierian]

The only alternative I can think of at this point is removing the plugin as part of our CI/CD release process. While that would certainly work, it feels brittle and a little hacky.