/// <summary>
/// Bind the pattern switch section, producing subsumption diagnostics.
/// </summary>
/// <param name="boundSwitchExpression"/>
/// <param name="node"/>
/// <param name="originalBinder"/>
/// <param name="defaultLabel">If a default label is found in this section, assigned that label</param>
/// <param name="someValueMatched">If a constant label is found that matches the constant input, assigned that label</param>
/// <param name="subsumption">A helper class that uses a decision tree to produce subsumption diagnostics.</param>
/// <param name="diagnostics"></param>
/// <returns></returns>
private BoundPatternSwitchSection BindPatternSwitchSection(
BoundExpression boundSwitchExpression,
SwitchSectionSyntax node,
Binder originalBinder,
ref BoundPatternSwitchLabel defaultLabel,
ref bool someValueMatched,
SubsumptionDiagnosticBuilder subsumption,
DiagnosticBag diagnostics)
{
// Bind match section labels
var boundLabelsBuilder = ArrayBuilder <BoundPatternSwitchLabel> .GetInstance();
var sectionBinder = originalBinder.GetBinder(node); // this binder can bind pattern variables from the section.
Debug.Assert(sectionBinder != null);
var labelsByNode = LabelsByNode;
foreach (var labelSyntax in node.Labels)
{
LabelSymbol label = labelsByNode[labelSyntax];
BoundPatternSwitchLabel boundLabel = BindPatternSwitchSectionLabel(sectionBinder, boundSwitchExpression, labelSyntax, label, ref defaultLabel, diagnostics);
bool valueMatched; // true if we find an unconditional constant label that matches the input constant's value
bool isReachable = subsumption.AddLabel(boundLabel, diagnostics, out valueMatched);
boundLabel = boundLabel.Update(boundLabel.Label, boundLabel.Pattern, boundLabel.Guard, isReachable && !someValueMatched);
someValueMatched |= valueMatched;
boundLabelsBuilder.Add(boundLabel);
}
// Bind switch section statements
var boundStatementsBuilder = ArrayBuilder <BoundStatement> .GetInstance();
foreach (var statement in node.Statements)
{
boundStatementsBuilder.Add(sectionBinder.BindStatement(statement, diagnostics));
}
return(new BoundPatternSwitchSection(node, sectionBinder.GetDeclaredLocalsForScope(node), boundLabelsBuilder.ToImmutableAndFree(), boundStatementsBuilder.ToImmutableAndFree()));
}
private BoundPatternSwitchLabel LowerSwitchLabel(BoundPatternSwitchLabel label)
{
return(label.Update(label.Label, _localRewriter.LowerPattern(label.Pattern), _localRewriter.VisitExpression(label.Guard), label.IsReachable));
}
/// <summary>
/// Bind the pattern switch section, producing subsumption diagnostics.
/// </summary>
/// <param name="node"/>
/// <param name="originalBinder"/>
/// <param name="defaultLabel">If a default label is found in this section, assigned that label</param>
/// <param name="someCaseMatches">If a case is found that would always match the input, set to true</param>
/// <param name="subsumption">A helper class that uses a decision tree to produce subsumption diagnostics.</param>
/// <param name="diagnostics"></param>
/// <returns></returns>
private BoundPatternSwitchSection BindPatternSwitchSection(
SwitchSectionSyntax node,
Binder originalBinder,
ref BoundPatternSwitchLabel defaultLabel,
ref bool someCaseMatches,
SubsumptionDiagnosticBuilder subsumption,
DiagnosticBag diagnostics)
{
// Bind match section labels
var boundLabelsBuilder = ArrayBuilder <BoundPatternSwitchLabel> .GetInstance();
var sectionBinder = originalBinder.GetBinder(node); // this binder can bind pattern variables from the section.
Debug.Assert(sectionBinder != null);
var labelsByNode = LabelsByNode;
bool?inputMatchesType(TypeSymbol patternType)
{
// use-site diagnostics will have been reported previously.
HashSet <DiagnosticInfo> useSiteDiagnostics = null;
return(ExpressionOfTypeMatchesPatternType(Conversions, SwitchGoverningType, patternType, ref useSiteDiagnostics, out _, SwitchGoverningExpression.ConstantValue, true));
}
foreach (var labelSyntax in node.Labels)
{
LabelSymbol label = labelsByNode[labelSyntax];
BoundPatternSwitchLabel boundLabel = BindPatternSwitchSectionLabel(sectionBinder, labelSyntax, label, ref defaultLabel, diagnostics);
bool isNotSubsumed = subsumption.AddLabel(boundLabel, diagnostics);
bool guardAlwaysSatisfied = boundLabel.Guard == null || boundLabel.Guard.ConstantValue == ConstantValue.True;
// patternMatches is true if the input expression is unconditionally matched by the pattern, false if it never matches, null otherwise.
// While subsumption would produce an error for an unreachable pattern based on the input's type, this is used for reachability (warnings),
// and takes the input value into account.
bool?patternMatches;
if (labelSyntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
patternMatches = null;
}
else if (boundLabel.Pattern.Kind == BoundKind.WildcardPattern)
{
// wildcard pattern matches anything
patternMatches = true;
}
else if (boundLabel.Pattern is BoundDeclarationPattern d)
{
// `var x` matches anything
// `Type x` matches anything of a subtype of `Type` except null
patternMatches = d.IsVar ? true : inputMatchesType(d.DeclaredType.Type);
}
else if (boundLabel.Pattern is BoundConstantPattern p)
{
// `case 2` matches the input `2`
patternMatches = SwitchGoverningExpression.ConstantValue?.Equals(p.ConstantValue);
}
else
{
patternMatches = null;
}
bool labelIsReachable = isNotSubsumed && !someCaseMatches && patternMatches != false;
boundLabel = boundLabel.Update(boundLabel.Label, boundLabel.Pattern, boundLabel.Guard, labelIsReachable);
boundLabelsBuilder.Add(boundLabel);
// labelWouldMatch is true if we find an unconditional (no `when` clause restriction) label that matches the input expression
bool labelWouldMatch = guardAlwaysSatisfied && patternMatches == true;
someCaseMatches |= labelWouldMatch;
}
// Bind switch section statements
var boundStatementsBuilder = ArrayBuilder <BoundStatement> .GetInstance();
foreach (var statement in node.Statements)
{
boundStatementsBuilder.Add(sectionBinder.BindStatement(statement, diagnostics));
}
return(new BoundPatternSwitchSection(node, sectionBinder.GetDeclaredLocalsForScope(node), boundLabelsBuilder.ToImmutableAndFree(), boundStatementsBuilder.ToImmutableAndFree()));
}