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List patterns: Slice value is assumed to be never null #57457

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merged 19 commits into from
Jan 20, 2022
Merged

List patterns: Slice value is assumed to be never null #57457

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104c8d9
Slice value is always assumed to be not null
alrz Oct 28, 2021
a128b59
Add test
alrz Nov 4, 2021
5127879
The annotation on the output type is ignored
alrz Nov 10, 2021
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alrz Nov 12, 2021
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Merge remote-tracking branch 'origin/main' into slice-value
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alrz Jan 11, 2022
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Merge remote-tracking branch 'origin/main' into slice-value
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alrz Jan 19, 2022
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6 changes: 5 additions & 1 deletion src/Compilers/CSharp/Portable/Binder/DecisionDagBuilder.cs
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Expand Up @@ -421,8 +421,12 @@ private static void MakeCheckNotNull(
ArrayBuilder<Tests> tests)
{
// Add a null test if needed
if (input.Type.CanContainNull())
if (input.Type.CanContainNull() &&
// The slice value is assumed to be never null
input.Source is not BoundDagSliceEvaluation)
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{
tests.Add(new Tests.One(new BoundDagNonNullTest(syntax, isExplicitTest, input)));
}
}

/// <summary>
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1 change: 1 addition & 0 deletions src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker_Patterns.cs
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Expand Up @@ -514,6 +514,7 @@ public PossiblyConditionalState Clone()
var outputSlot = makeDagTempSlot(type, output);
Debug.Assert(outputSlot > 0);
addToTempMap(output, outputSlot, type.Type);
this.State[outputSlot] = NullableFlowState.NotNull; // Slice value is assumed to be never null
Comment on lines 516 to +517
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@alrz alrz Jan 19, 2022 •
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❓ Should we also strip the annotation on the return type for semantic model?

I am not sure if hovering over [.. var variable] shows a nullable type (probably shouldn't?)

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The var will definitely have a ?, because it always does. Theoretically, though, it should say that variable is considered not null here.

break;
}
case BoundDagAssignmentEvaluation e:
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4 changes: 2 additions & 2 deletions src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTestBase.cs
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Expand Up @@ -441,12 +441,12 @@ protected static void AssertEmpty(SymbolInfo info)
Assert.Equal(CandidateReason.None, info.CandidateReason);
}

protected static void VerifyDecisionDagDump<T>(Compilation comp, string expectedDecisionDag)
protected static void VerifyDecisionDagDump<T>(Compilation comp, string expectedDecisionDag, int index = 0)
where T : CSharpSyntaxNode
{
#if DEBUG
var tree = comp.SyntaxTrees.First();
var node = tree.GetRoot().DescendantNodes().OfType<T>().First();
var node = tree.GetRoot().DescendantNodes().OfType<T>().ElementAt(index);
var model = (CSharpSemanticModel)comp.GetSemanticModel(tree);
var binder = model.GetEnclosingBinder(node.SpanStart);
var decisionDag = node switch
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