CSIsNull002 - Bad code fix offered in Linq to sql expression

[elachlan]

I have a linq query from a DbContext with the following in the where clause:

(toDate != null || a.Date <= toDate)

toDate is a nullable date. So we check it for null prior to doing a filter using it.

CSIsNull002 matches to this and suggests is not null, but when the refactor is made, I get the error:

CS8122	An expression tree may not contain an 'is' pattern-matching operator.

[elachlan]

This is a bad example because the logic is wrong, but it does result in the error.

[AArnott]

This seems very similar to #3, and I'm surprised this is still a bug since that was supposedly fixed.

[elachlan]

@AArnott I ran into this again, are you able to have a look?

[AArnott]

@elachlan what version are you using?

We have what looks like a test for this case already:

CSharpIsNull/test/CSharpIsNullAnalyzer.Tests/CSIsNull002Tests.cs

Lines 211 to 240 in 4f23ce0

	[Fact]
	public async Task NotEqualsNullInExpressionTree_OffersOneCodeFix()
	{
	string source = @"
	using System;
	using System.Linq.Expressions;
	class Test
	{
	void Method()
	{
	_ = (Expression<Func<string, bool>>)(s => s [|!= null|]);
	}
	}";
	string fixedSource = @"
	using System;
	using System.Linq.Expressions;
	class Test
	{
	void Method()
	{
	_ = (Expression<Func<string, bool>>)(s => s is object);
	}
	}";
	await VerifyCS.VerifyCodeFixAsync(source, fixedSource, CSIsNull002Fixer.IsObjectEquivalenceKey);
	await VerifyCS.VerifyCodeFixAsync(source, source, CSIsNull002Fixer.IsNotNullEquivalenceKey); // assert that this fix is not offered.
	}

I even added a new test with compound logic to match yours, but it still did not offer a is not null code fix:

    [Fact]
    public async Task NotEqualsNullInExpressionTree_ProducesNoDiagnostic()
    {
        string source = @"
using System;
using System.Linq.Expressions;
class Test
{
    void Method(int o)
    {
        bool? b = true;
        Expression<Func<bool>> e = () => (b != null || 3 < 5);
    }
}";

        await VerifyCS.VerifyAnalyzerAsync(source);
    }

Now, in that case, no diagnostic was created either, which isn't good and I'm looking into that. But it's not the issue you're reporting.

[AArnott]

#70 is the fix to what I found, but again, that isn't the issue you're reporting.