HaveElementAt

[jnyrup]

I suspect this might be related to the other issue about the syntax tree?

public class MyClass
{
    public string Message { get; }
}

var list = new List<MyClass>();

list[0].Message.Should().Be(""); // throws exception

System.InvalidCastException : Unable to cast object of type 'Microsoft.CodeAnalysis.CSharp.Syntax.MemberAccessExpressionSyntax' to type 'Microsoft.CodeAnalysis.CSharp.Syntax.ElementAccessExpressionSyntax'.
   at FluentAssertions.Analyzers.NodeReplacement.RemoveAndRetrieveIndexerArgumentsNodeReplacement.ComputeNew(LinkedListNode`1 listNode)
   at FluentAssertions.Analyzers.FluentAssertionsCodeFixProvider.GetNewStatement(ExpressionStatementSyntax statement,NodeReplacement replacement)
   at FluentAssertions.Analyzers.CollectionShouldHaveElementAtCodeFix.GetNewStatement(ExpressionStatementSyntax statement,FluentAssertionsDiagnosticProperties properties)
   at async FluentAssertions.Analyzers.FluentAssertionsCodeFixProvider.RewriteAssertion(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetChangedSolutionAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.ComputeOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.ComputePreviewOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetPreviewOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedAction.GetPreviewResultAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedActionWithNestedFlavors.<>c__DisplayClass11_0.<GetPreviewAsync>b__0(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)

If I rewrite the assertion to be valid for all enumerables

list.ElementAt(0).Message.Should().Be("");

it is simplified into the invalid

list.Message.Should().HaveElementAt(0, "");

[Meir017]

just to be sure,

list.ElementAt(0).Message.Should().Be("");

should not trigger any analyzers, right?

[Meir017]

right now the way to discover this scenario is if the SimpleMemberAccessExpression representing the Should method doesn't have an InvocationExpression as it's Expression then we have a property accessor and should not trigger the analyzer.

The exception I see is having cases like this

list.ElementAt(0).ToString().Should().Be(flag);

where the user is doing something weired...

[jnyrup]

You are quite good at giving hints :)
A simplified version of the code causing the exception:

string str = "a, b";
string[] splitLines = str.Split(',');

splitLines[0].Trim().Should().Be("a");
splitLines[1].Trim().Should().Be("b");

[Meir017]

I created a branch for testing stuff, I have a lead on the new visitor algorithm - https://github.com/fluentassertions/fluentassertions.analyzers/blob/playground/src/FluentAssertions.Analyzers/Poc/PocAnalyzer.cs

[Meir017]

@jnyrup I managed to create an analyzer using the new visitor 052f272 .

I think the next stage will be to add positive tests that trigger the analyzers and negative tests that don't trigger any analyzers

[Meir017]

@jnyrup notice the tests in the file https://github.com/fluentassertions/fluentassertions.analyzers/blob/feature/GH-13/src/FluentAssertions.Analyzers.Tests/Tips/SanityTests.cs

Are there cases related to the exception in this issue you can think of that I missed?