New Analyzer: Warn when calling Enumerable.Cast<T>/OfType<T> with incompatible types

[fowl2]

Warn if use of Enumerable.Cast<T> would always fail at runtime or OfType<T>() would provably result in an empty sequence, because we can see that the input type in the sequence will never be the specified type.

RuleId: CA2021
Category: Reliability

related: #3608, dotnet/runtime#33770

• Tests pass
• Targeted to release/7.0.1xx main
• Run against
  • dotnet/roslyn-analyzers
  • dotnet/runtime
  • dotnet/roslyn
• Docs

[dnfadmin]

All CLA requirements met.

[fowl2]

That should be all the warnings resolved except for the rule id. Not sure how those are are assigned.

[buyaa-n]

@fowl2 The analyzer proposal has not yet been approved, please wait until the proposal goes through API review

[carlossanlop]

The proposal has been approved so we can unblock the PR, @buyaa-n

[buyaa-n]

Overall looks good @fowl2 thank you for your contribution, added few comment, and seems we could add some more unit tests.
Not sure if you read our Definition of done list, it would be great if you could try testing the new analyzer with runtime repo, please let us know if you would like to give it a try

[mavasani]

Please retarget this PR to https://github.com/dotnet/roslyn-analyzers/tree/release/6.0.1xx-preview1

[mavasani]

Please retarget this PR to https://github.com/dotnet/roslyn-analyzers/tree/release/6.0.1xx-preview1

[buyaa-n]

@fowl2 could you address the comments? Do you need a help with anything?

Also please retarget to https://github.com/dotnet/roslyn-analyzers/tree/release/6.0.1xx

[fowl2]

@buyaa-n sorry I haven't had time to look at this - looks like I'll have some spare time this week to get back to you

[danmoseley]

@fowl2 could you give us an update? It would be great to have this analyzer. Do you expect to have more time?

[buyaa-n]

ping @fowl2 again, are you planning to work on it?

[Youssef1313]

@Youssef1313 do you have any hints as to how to run test against dotnet/roslyn-analyzers?

Can you try the instructions here?

[fowl2]

Yes that's what I was trying. See my previous comment :)

[Youssef1313]

Probably @buyaa-n or @mavasani can help better here.

[buyaa-n]

do you have any hints as to how to run test against dotnet/roslyn-analyzers?

Sorry for the late reply @fowl2, apparently the repo's dogfooding analyzer is updated

roslyn-analyzers/src/Directory.Build.props

Line 38 in 086d1cc

<PackageReference Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="$(DogfoodNetAnalyzersVersion)" />

The current version is

roslyn-analyzers/eng/Versions.props

Line 49 in 92d7d36

<DogfoodNetAnalyzersVersion>5.0.4-preview1.21126.5</DogfoodNetAnalyzersVersion>

So you can use/copy DLLs from artifacts\bin\Microsoft.CodeAnalysis.CSharp.NetAnalyzers\Debug\netstandard2.0 and replace with the ones in %USERPROFILE%\.nuget\packages\Microsoft.CodeAnalysis.NetAnalyzers\%RUNTIMEPACKAGEVERSION%\analyzers\dotnet\cs (just like testing the runtime repo)

[fowl2]

done:

• rebased on main: still builds ✅🎉
• got it running against roslyn-analyzers: no problems found
• double checked by adding a problem: found 🎉

to be:

• check against runtime (ran into some python dep issue) and roslyn (unrelated laptop death)

[fowl2]

I've rebased to main, changed to new diagnostic ID (again) and updated to the new DiagnosticDescriptor/LocalizableString pattern.

Ran out of time/cpu again trying to run it against runtime and rosyln, could I ask someone else have a go to help get this over the line? :)

[buyaa-n]

Ran out of time/cpu again trying to run it against runtime and rosyln, could I ask someone else have a go to help get this over the line? :)

Tested with runtime looks good and no diagnostic found, thank you. We can skip testing with roslyn.

Overall looks great to me, left a few questions

[buyaa-n]

Thank you @fowl2 LGTM!

@mavasani please look at the open questions and you also have out-dated change request

Stale