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AbstractFlowPass.VisitIsPatternExpression - add handling for list-pattern specific patterns #59285

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merged 4 commits into from
Feb 15, 2022
Merged

AbstractFlowPass.VisitIsPatternExpression - add handling for list-pattern specific patterns #59285

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e1714e4
Fix definite assignment crash with list-patterns
jcouv Feb 4, 2022
defa29e
Address more unhandled cases
jcouv Feb 7, 2022
75945ae
Add assertion
jcouv Feb 7, 2022
9bf427c
tweak comment
jcouv Feb 15, 2022
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1 change: 1 addition & 0 deletions src/Compilers/CSharp/Portable/FlowAnalysis/AbstractFlowPass.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1035,6 +1035,7 @@ static bool patternMatchesNull(BoundPattern pattern)
case BoundITuplePattern:
case BoundRelationalPattern:
case BoundDeclarationPattern:
case BoundListPattern:
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@alrz alrz Feb 4, 2022 •
edited by jcouv
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There's another switch with a missing case in patternMatchesNull above.

It's not clear how an exhaustive switch is supposed to help here since not every pattern node is going through this check as demonstrated in this bug. Unless there's a compile-time diagnostic, you'd need to scan the code to find each instance or else, wait for a crash later. Would it make sense to have a safe default with Assert(false) instead of throwing right away? (or make it so that every pattern is visited here regardless of the source tree) #Resolved

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Thanks. Fixed that other case, plus two more (for slices).

I added an assertion that should help catch this problem with future patterns.

return null;
default:
throw ExceptionUtilities.UnexpectedValue(pattern.Kind);
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32 changes: 32 additions & 0 deletions src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests_ListPatterns.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -8121,4 +8121,36 @@ public void ListPattern_NullTestOnSlice()
Diagnostic(ErrorCode.ERR_SwitchCaseSubsumed, "[1,2,3]").WithLocation(15, 10)
);
}

[Fact, WorkItem(58738, "https://github.com/dotnet/roslyn/issues/58738")]
public void ListPattern_DefiniteAssignmentOnErrorCode()
{
var source = @"
var a = new[] { 1 };

if (a is [var x] and x is [1])
{
}

var b = new[] { true };
if ((b is [var y] and y) is [true])
{
}
";
var comp = CreateCompilationWithIndexAndRangeAndSpan(new[] { source, TestSources.GetSubArray });
comp.VerifyEmitDiagnostics(
// (4,22): error CS0029: Cannot implicitly convert type 'int' to 'int[]'
// if (a is [var x] and x is [1])
Diagnostic(ErrorCode.ERR_NoImplicitConv, "x").WithArguments("int", "int[]").WithLocation(4, 22),
// (4,27): error CS0021: Cannot apply indexing with [] to an expression of type 'bool'
// if (a is [var x] and x is [1])
Diagnostic(ErrorCode.ERR_BadIndexLHS, "[1]").WithArguments("bool").WithLocation(4, 27),
// (9,23): error CS0029: Cannot implicitly convert type 'bool' to 'bool[]'
// if ((b is [var y] and y) is [true])
Diagnostic(ErrorCode.ERR_NoImplicitConv, "y").WithArguments("bool", "bool[]").WithLocation(9, 23),
// (9,29): error CS0021: Cannot apply indexing with [] to an expression of type 'bool'
// if ((b is [var y] and y) is [true])
Diagnostic(ErrorCode.ERR_BadIndexLHS, "[true]").WithArguments("bool").WithLocation(9, 29)
);
}
}