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Input param postconditions #49576

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merged 2 commits into from
Dec 7, 2020
Merged

Input param postconditions #49576

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e552f25
Fix [AllowNull] string s scenario
RikkiGibson Nov 23, 2020
c730564
Remove misleading comment
RikkiGibson Dec 2, 2020
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41 changes: 30 additions & 11 deletions src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1850,6 +1850,22 @@ private void ReportNullableAssignmentIfNecessary(
ReportDiagnostic(ErrorCode.WRN_NullReferenceArgument, location,
GetParameterAsDiagnosticArgument(parameterOpt),
GetContainingSymbolAsDiagnosticArgument(parameterOpt));

if (targetType.Type.IsPossiblyNullableReferenceTypeTypeParameter())
{
var slotBuilder = ArrayBuilder<int>.GetInstance();
GetSlotsToMarkAsNotNullable(value, slotBuilder);
foreach (var slot in slotBuilder)
{
Debug.Assert(State[slot] == NullableFlowState.MaybeDefault);
State[slot] = NullableFlowState.MaybeNull;
}
slotBuilder.Free();
}
else
{
LearnFromNonNullTest(value, ref State);
}
}
else if (useLegacyWarnings)
{
Expand Down Expand Up @@ -4230,7 +4246,7 @@ private static TypeWithState GetNullCoalescingResultType(TypeWithState rightResu

// Per LDM 2019-02-13 decision, the result of a conditional access "may be null" even if
// both the receiver and right-hand-side are believed not to be null.
SetResultType(node, TypeWithState.Create(resultType, NullableFlowState.MaybeNull));
SetResultType(node, TypeWithState.Create(resultType, NullableFlowState.MaybeDefault));
_currentConditionalReceiverVisitResult = default;
_lastConditionalAccessSlot = previousConditionalAccessSlot;
return null;
Expand Down Expand Up @@ -5308,7 +5324,10 @@ private void VisitArgumentConversionAndInboundAssignmentsAndPreConditions(
stateForLambda: result.StateForLambda);

// If the parameter has annotations, we perform an additional check for nullable value types
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nullable value types [](start = 96, length = 20)

Is this just for nullable value types?

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Yes, for example in the case of a parameter [DisallowNull] string? s we can adjust the type to just string and then visit the conversion. But in the case of [DisallowNull] int? i we can't adjust the type in that way. SharpLab. Note particularly the difference in diagnostic IDs.

CheckDisallowedNullAssignment(stateAfterConversion, parameterAnnotations, argumentNoConversion.Syntax.Location);
if (CheckDisallowedNullAssignment(stateAfterConversion, parameterAnnotations, argumentNoConversion.Syntax.Location))
{
LearnFromNonNullTest(argumentNoConversion, ref State);
}
SetResultType(argumentNoConversion, stateAfterConversion, updateAnalyzedNullability: false);
}
break;
Expand Down Expand Up @@ -5340,19 +5359,23 @@ private void VisitArgumentConversionAndInboundAssignmentsAndPreConditions(
Debug.Assert(!this.IsConditionalState);
}

private void CheckDisallowedNullAssignment(TypeWithState state, FlowAnalysisAnnotations annotations, Location location, BoundExpression? boundValueOpt = null)
/// <summary>Returns <see langword="true"/> if this is an assignment forbidden by DisallowNullAttribute, otherwise <see langword="false"/>.</summary>
private bool CheckDisallowedNullAssignment(TypeWithState state, FlowAnalysisAnnotations annotations, Location location, BoundExpression? boundValueOpt = null)
{
if (boundValueOpt is { WasCompilerGenerated: true })
{
// We need to skip `return backingField;` in auto-prop getters
return;
return false;
}

// We do this extra check for types whose non-nullable version cannot be represented
if (IsDisallowedNullAssignment(state, annotations))
{
ReportDiagnostic(ErrorCode.WRN_DisallowNullAttributeForbidsMaybeNullAssignment, location);
return true;
}

return false;
}

private static bool IsDisallowedNullAssignment(TypeWithState valueState, FlowAnalysisAnnotations targetAnnotations)
Expand Down Expand Up @@ -5595,10 +5618,6 @@ void learnFromPostConditions(BoundExpression argument, TypeWithAnnotations param
// Note: NotNull = NotNullWhen(true) + NotNullWhen(false)
bool notNullWhenTrue = (parameterAnnotations & FlowAnalysisAnnotations.NotNullWhenTrue) != 0;
bool notNullWhenFalse = (parameterAnnotations & FlowAnalysisAnnotations.NotNullWhenFalse) != 0;
bool disallowNull = (parameterAnnotations & FlowAnalysisAnnotations.DisallowNull) != 0;
bool setNotNullFromParameterType = !argument.IsSuppressed
&& !parameterType.Type.IsPossiblyNullableReferenceTypeTypeParameter()
&& parameterType.NullableAnnotation.IsNotAnnotated();

// Note: MaybeNull = MaybeNullWhen(true) + MaybeNullWhen(false)
bool maybeNullWhenTrue = (parameterAnnotations & FlowAnalysisAnnotations.MaybeNullWhenTrue) != 0;
Expand All @@ -5608,7 +5627,7 @@ void learnFromPostConditions(BoundExpression argument, TypeWithAnnotations param
{
LearnFromNullTest(argument, ref State);
}
else if (((notNullWhenTrue && notNullWhenFalse) || disallowNull || setNotNullFromParameterType)
else if (notNullWhenTrue && notNullWhenFalse
&& !IsConditionalState
&& !(maybeNullWhenTrue || maybeNullWhenFalse))
{
Expand Down Expand Up @@ -7045,9 +7064,9 @@ private TypeWithState VisitUserDefinedConversion(
diagnosticLocation: operandLocation);

// in the case of a lifted conversion, we assume that the call to the operator occurs only if the argument is not-null
if (!isLiftedConversion)
if (!isLiftedConversion && CheckDisallowedNullAssignment(operandType, parameterAnnotations, conversionOperand.Syntax.Location))
{
CheckDisallowedNullAssignment(operandType, parameterAnnotations, conversionOperand.Syntax.Location);
LearnFromNonNullTest(conversionOperand, ref State);
}

// method parameter type -> method return type
Expand Down
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