Improve the diagnostics that are emitted when a package dependency specifies a non-existent branch or commit

[abertelrud]

This also sets the code up to make it easier to do other similar heuristics as needed, and as a bonus, adds one that is related to the master -> main renaming (suggesting main if master is requested and doesn't exist, but main does). There isn't yet any support for fix-its in SwiftPM, but this would be a case for such a facility once it is supported.

Note that tags go through different processing, since they are the inputs to the semantic versioning and missing tags are reported differently. There is no way in SwiftPM to define an explicit dependency on a non-semver tag, which is why this code only needs to handle branches and commits.

The error message does not list all the branches, since there can be many, but that could be another future improvement (or at least to list all the branches whose names are similar to what was requested).

rdar://34099187

[abertelrud]

@swift-ci please smoke test

[compnerd]

Hmm, I seem to be getting an error on Windows after this change:

cmd.exe /C "cd . && S:\22\toolchain-windows-x64\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin\swiftc.exe -target x86_64-unknown-windows-msvc -output-file-map Sources\PackageGraph\CMakeFiles\PackageGraph.dir\output-file-map.json -incremental -j 48 -emit-library -o bin\PackageGraph.dll -module-name PackageGraph -module-link-name PackageGraph -emit-module -emit-module-path swift\PackageGraph.swiftmodule -emit-dependencies -DPackageGraph_EXPORTS -resource-dir "S:\22/sdk-windows-x64/Library/Developer/Platforms/Windows.platform/Developer/SDKs/Windows.sdk/usr/lib/swift" -LS:\22/sdk-windows-x64/Library/Developer/Platforms/Windows.platform/Developer/SDKs/Windows.sdk/usr/lib/swift/windows -O -swift-version 5 -libc MD   -Xcc -D_CRT_SECURE_NO_WARNINGS -I swift -I S:\22\b\swift-tools-support-core\swift -I S:\22\s\swift-tools-support-core\Sources\TSCclibc\include -I S:\22\b\swift-llbuild\products\llbuildSwift -I S:\22\s\swift-llbuild\products\libllbuild\include S:\22\s\swift-package-manager\Sources\PackageGraph\CheckoutState.swift S:\22\s\swift-package-manager\Sources\PackageGraph\DependencyResolver.swift S:\22\s\swift-package-manager\Sources\PackageGraph\PackageGraph.swift S:\22\s\swift-package-manager\Sources\PackageGraph\PackageGraphLoader.swift S:\22\s\swift-package-manager\Sources\PackageGraph\PackageGraphRoot.swift S:\22\s\swift-package-manager\Sources\PackageGraph\PinsStore.swift S:\22\s\swift-package-manager\Sources\PackageGraph\Pubgrub.swift S:\22\s\swift-package-manager\Sources\PackageGraph\RawPackageConstraints.swift S:\22\s\swift-package-manager\Sources\PackageGraph\RepositoryPackageContainerProvider.swift S:\22\s\swift-package-manager\Sources\PackageGraph\VersionSetSpecifier.swift    -Xlinker -implib:lib\PackageGraph.lib -L S:/22/b/swift-package-manager/lib  -L S:/22/b/swift-package-manager/lib  -L S:/22/b/swift-package-manager/lib  -L S:/22/b/swift-package-manager/lib  -L S:/22/b/swift-llbuild/lib  -L S:/22/b/swift-llbuild/lib  -L S:/22/b/swift-tools-support-core/lib  -L S:/22/b/swift-tools-support-core/lib  -L S:/22/b/swift-tools-support-core/lib  -L S:/22/b/swift-tools-support-core/lib lib\PackageLoading.lib  lib\PackageModel.lib  lib\SourceControl.lib  lib\SPMLLBuild.lib  S:\22\b\swift-llbuild\lib\llbuildSwift.lib  S:\22\b\swift-llbuild\lib\llbuild.lib  S:\22\b\swift-tools-support-core\lib\TSCUtility.lib  S:\22\b\swift-tools-support-core\lib\TSCBasic.lib  S:\22\b\swift-tools-support-core\lib\TSCLibc.lib  S:\22\b\swift-tools-support-core\lib\TSCclibc.lib  -lFoundation.lib  -lFoundationNetworking.lib && cd ."
S:\22\s\swift-package-manager\Sources\PackageGraph\RepositoryPackageContainerProvider.swift:399:91: error: value of type 'ProcessResult.Error' has no member 'description'
            if let gitInvocationError = error as? ProcessResult.Error, gitInvocationError.description.contains("Needed a single revision") {
                                                                       ~~~~~~~~~~~~~~~~~~ ^~~~~~~~~~~

[compnerd]

swiftlang/swift-tools-support-core#124 should repair the build

[abertelrud]

Thanks @compnerd and apologies. It looks as thought the #endif in TSC was misplaced all along, I think? Can't wait to get Windows CI runs, since I don't have a Windows box to test changes with.