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

dotnet · Jan 20, 2022 · 305a91c · 305a91c
1 parent e70912b
commit 305a91c
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Showing 5 changed files with 298 additions and 155 deletions.
diff --git a/src/Compilers/CSharp/Portable/Binder/DecisionDagBuilder.cs b/src/Compilers/CSharp/Portable/Binder/DecisionDagBuilder.cs
@@ -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)
+ {
  tests.Add(new Tests.One(new BoundDagNonNullTest(syntax, isExplicitTest, input)));
+ }
  }
 
  /// <summary>

diff --git a/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker_Patterns.cs b/src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker_Patterns.cs
@@ -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
  break;
  }
  case BoundDagAssignmentEvaluation e:

diff --git a/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTestBase.cs b/src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTestBase.cs
@@ -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