private BoundPatternSwitchSection BindPatternSwitchSection(
BoundExpression boundSwitchExpression,
SwitchSectionSyntax node,
Binder originalBinder,
ref BoundPatternSwitchLabel defaultLabel,
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);
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()));
}
/// <summary>
/// Bind the pattern switch labels, reporting in the process which cases are subsumed. The strategy
/// implemented with the help of <see cref="SubsumptionDiagnosticBuilder"/>, is to start with an empty
/// decision tree, and for each case we visit the decision tree to see if the case is subsumed. If it
/// is, we report an error. If it is not subsumed and there is no guard expression, we then add it to
/// the decision tree.
/// </summary>
private ImmutableArray <BoundPatternSwitchSection> BindPatternSwitchSections(
Binder originalBinder,
out BoundPatternSwitchLabel defaultLabel,
out bool isComplete,
out bool someCaseMatches,
DiagnosticBag diagnostics)
{
defaultLabel = null;
// someCaseMatches will be set to true if some single case label would handle all inputs
someCaseMatches = false;
// Bind match sections
var boundPatternSwitchSectionsBuilder = ArrayBuilder <BoundPatternSwitchSection> .GetInstance();
SubsumptionDiagnosticBuilder subsumption = new SubsumptionDiagnosticBuilder(ContainingMemberOrLambda, SwitchSyntax, this.Conversions, SwitchGoverningType);
foreach (var sectionSyntax in SwitchSyntax.Sections)
{
var section = BindPatternSwitchSection(sectionSyntax, originalBinder, ref defaultLabel, ref someCaseMatches, subsumption, diagnostics);
boundPatternSwitchSectionsBuilder.Add(section);
}
isComplete = defaultLabel != null || subsumption.IsComplete || someCaseMatches;
return(boundPatternSwitchSectionsBuilder.ToImmutableAndFree());
}
/// <summary>
/// Bind the pattern switch labels, reporting in the process which cases are subsumed. The strategy,
/// implemented with the help of <see cref="SubsumptionDiagnosticBuilder"/>, is to start with an empty
/// decision tree, and for each case we visit the decision tree to see if the case is subsumed. If it
/// is, we report an error. If it is not subsumed and there is no guard expression, we then add it to
/// the decision tree.
/// </summary>
private ImmutableArray <BoundPatternSwitchSection> BindPatternSwitchSections(
Binder originalBinder,
out BoundPatternSwitchLabel defaultLabel,
out bool isComplete,
DiagnosticBag diagnostics)
{
defaultLabel = null;
// true if we found a case label whose value is the same as the input expression's constant value
bool someValueMatched = false;
// Bind match sections
var boundPatternSwitchSectionsBuilder = ArrayBuilder <BoundPatternSwitchSection> .GetInstance();
SubsumptionDiagnosticBuilder subsumption = new SubsumptionDiagnosticBuilder(ContainingMemberOrLambda, SwitchSyntax, this.Conversions, SwitchGoverningExpression);
foreach (var sectionSyntax in SwitchSyntax.Sections)
{
boundPatternSwitchSectionsBuilder.Add(BindPatternSwitchSection(
SwitchGoverningExpression, sectionSyntax, originalBinder, ref defaultLabel, ref someValueMatched, subsumption, diagnostics));
}
isComplete = defaultLabel != null || subsumption.IsComplete || someValueMatched;
return(boundPatternSwitchSectionsBuilder.ToImmutableAndFree());
}
private BoundPatternSwitchLabel BindPatternSwitchSectionLabel(
Binder sectionBinder, BoundExpression boundSwitchExpression, SwitchLabelSyntax node, LabelSymbol label, ref BoundPatternSwitchLabel defaultLabel, DiagnosticBag diagnostics)
{
switch (node.Kind())
{
case SyntaxKind.CaseSwitchLabel:
{
var caseLabelSyntax = (CaseSwitchLabelSyntax)node;
bool wasExpression;
var pattern = sectionBinder.BindConstantPattern(
node, boundSwitchExpression, boundSwitchExpression.Type, caseLabelSyntax.Value, node.HasErrors, diagnostics, out wasExpression, wasSwitchCase: true);
bool hasErrors = pattern.HasErrors;
var constantValue = pattern.ConstantValue;
if (!hasErrors &&
(object)constantValue != null &&
pattern.Value.Type == SwitchGoverningType &&
this.FindMatchingSwitchCaseLabel(constantValue, caseLabelSyntax) != label)
{
diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, pattern.ConstantValue.GetValueToDisplay() ?? label.Name);
hasErrors = true;
}
return(new BoundPatternSwitchLabel(node, label, pattern, null, hasErrors));
}
case SyntaxKind.DefaultSwitchLabel:
{
var defaultLabelSyntax = (DefaultSwitchLabelSyntax)node;
var pattern = new BoundWildcardPattern(node);
bool hasErrors = pattern.HasErrors;
if (defaultLabel != null)
{
diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, label.Name);
hasErrors = true;
}
// Note that this is semantically last! The caller will place it in the decision tree
// in the final position.
defaultLabel = new BoundPatternSwitchLabel(node, label, pattern, null, hasErrors);
return(defaultLabel);
}
case SyntaxKind.CasePatternSwitchLabel:
{
var matchLabelSyntax = (CasePatternSwitchLabelSyntax)node;
var pattern = sectionBinder.BindPattern(
matchLabelSyntax.Pattern, boundSwitchExpression, boundSwitchExpression.Type, node.HasErrors, diagnostics, wasSwitchCase: true);
return(new BoundPatternSwitchLabel(node, label, pattern,
matchLabelSyntax.WhenClause != null ? sectionBinder.BindBooleanExpression(matchLabelSyntax.WhenClause.Condition, diagnostics) : null, node.HasErrors));
}
default:
throw ExceptionUtilities.UnexpectedValue(node);
}
}
/// <summary>
/// Add the case label to the subsumption tree. Return true if the label is reachable
/// (not subsumed) given the governing expression's type and previously added labels.
/// </summary>
internal bool AddLabel(BoundPatternSwitchLabel label, DiagnosticBag diagnostics)
{
// Use site diagnostics are reported (and cleared) by this method.
// So they should be empty when we start.
Debug.Assert(_useSiteDiagnostics.Count == 0);
if (label.Syntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
// the default case label is always considered reachable.
return(true);
}
try
{
// For purposes of subsumption, we do not take into consideration the value
// of the input expression. Therefore we consider null possible if the type permits.
var inputCouldBeNull = _subsumptionTree.Type.CanContainNull();
var subsumedErrorCode = CheckSubsumed(label.Pattern, _subsumptionTree, inputCouldBeNull: inputCouldBeNull);
if (subsumedErrorCode != 0)
{
if (!label.HasErrors && subsumedErrorCode != ErrorCode.ERR_NoImplicitConvCast)
{
diagnostics.Add(subsumedErrorCode, label.Pattern.Syntax.Location);
}
return(false);
}
var guardAlwaysSatisfied = label.Guard == null || label.Guard.ConstantValue == ConstantValue.True;
if (guardAlwaysSatisfied)
{
// Only unconditional switch labels contribute to subsumption
if (AddToDecisionTree(_subsumptionTree, null, label) == null && !label.Pattern.HasErrors)
{
// Since the pattern was not subsumed, we should be able to add it to the decision tree
throw ExceptionUtilities.Unreachable;
}
}
return(true);
}
finally
{
// report the use-site diagnostics
diagnostics.Add(label.Syntax.Location, _useSiteDiagnostics);
_useSiteDiagnostics.Clear();
}
}
public Guarded(
BoundExpression expression,
TypeSymbol type,
ImmutableArray <KeyValuePair <BoundExpression, BoundExpression> > bindings,
SyntaxNode sectionSyntax,
BoundExpression guard,
BoundPatternSwitchLabel label)
: base(expression, type, null)
{
this.Guard = guard;
this.Label = label;
this.Bindings = bindings;
this.SectionSyntax = sectionSyntax;
Debug.Assert(guard?.ConstantValue != ConstantValue.False);
base.MatchIsComplete =
(guard == null) || (guard.ConstantValue == ConstantValue.True);
}
/// <summary>
/// Bind a pattern switch label in order to force inference of the type of pattern variables.
/// </summary>
internal override void BindPatternSwitchLabelForInference(CasePatternSwitchLabelSyntax node, DiagnosticBag diagnostics)
{
// node should be a label of this switch statement.
Debug.Assert(this.SwitchSyntax == node.Parent.Parent);
// This simulates enough of the normal binding path of a switch statement to cause
// the label's pattern variables to have their types inferred, if necessary.
// It also binds the when clause, and therefore any pattern and out variables there.
BoundPatternSwitchLabel defaultLabel = null;
BindPatternSwitchSectionLabel(
sectionBinder: GetBinder(node.Parent),
node: node,
label: LabelsByNode[node],
defaultLabel: ref defaultLabel,
diagnostics: diagnostics);
}
private DecisionTree LowerToDecisionTree(
BoundExpression loweredExpression,
BoundPatternSwitchStatement node)
{
var loweredDecisionTree = DecisionTree.Create(loweredExpression, loweredExpression.Type, _enclosingSymbol);
BoundPatternSwitchLabel defaultLabel = null;
SyntaxNode defaultSection = null;
foreach (var section in node.SwitchSections)
{
var sectionSyntax = (SyntaxNode)section.Syntax;
foreach (var label in section.SwitchLabels)
{
var loweredLabel = LowerSwitchLabel(label);
if (loweredLabel.Syntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
if (defaultLabel != null)
{
// duplicate switch label will have been reported during initial binding.
}
else
{
defaultLabel = loweredLabel;
defaultSection = sectionSyntax;
}
}
else
{
Syntax = label.Syntax;
AddToDecisionTree(loweredDecisionTree, sectionSyntax, loweredLabel);
}
}
}
if (defaultLabel != null)
{
Add(loweredDecisionTree, (e, t) => new DecisionTree.Guarded(loweredExpression, loweredExpression.Type, default(ImmutableArray <KeyValuePair <BoundExpression, BoundExpression> >), defaultSection, null, defaultLabel));
}
// We discard use-site diagnostics, as they have been reported during initial binding.
_useSiteDiagnostics.Clear();
return(loweredDecisionTree);
}
private void AddToDecisionTree(DecisionTree decisionTree, BoundPatternSwitchLabel label)
{
var pattern = label.Pattern;
var guard = label.Guard;
if (guard?.ConstantValue == ConstantValue.False)
{
return;
}
switch (pattern.Kind)
{
case BoundKind.ConstantPattern:
{
var constantPattern = (BoundConstantPattern)pattern;
AddByValue(decisionTree, constantPattern.Value, (e, t) => new DecisionTree.Guarded(e, t, default(ImmutableArray <KeyValuePair <BoundExpression, BoundExpression> >), _section, guard, label));
break;
}
case BoundKind.DeclarationPattern:
{
var declarationPattern = (BoundDeclarationPattern)pattern;
DecisionMaker maker = (e, t) => new DecisionTree.Guarded(e, t, ImmutableArray.Create(new KeyValuePair <BoundExpression, BoundExpression>(e, declarationPattern.VariableAccess)), _section, guard, label);
if (declarationPattern.IsVar)
{
Add(decisionTree, maker);
}
else
{
AddByType(decisionTree, declarationPattern.DeclaredType.Type, maker);
}
break;
}
case BoundKind.WildcardPattern:
// We do not yet support a wildcard pattern syntax. It is used exclusively
// to model the "default:" case, which is handled specially in the caller.
default:
throw ExceptionUtilities.UnexpectedValue(pattern.Kind);
}
}
private DecisionTree LowerToDecisionTree(
BoundExpression loweredExpression,
BoundPatternSwitchStatement node)
{
var loweredDecisionTree = CreateEmptyDecisionTree(loweredExpression);
BoundPatternSwitchLabel defaultLabel = null;
SyntaxNode defaultSection = null;
foreach (var section in node.SwitchSections)
{
var sectionSyntax = section.Syntax;
foreach (var label in section.SwitchLabels)
{
var loweredLabel = LowerSwitchLabel(label);
if (loweredLabel.Syntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
if (defaultLabel != null)
{
// duplicate switch label will have been reported during initial binding.
}
else
{
defaultLabel = loweredLabel;
defaultSection = sectionSyntax;
}
}
else
{
AddToDecisionTree(loweredDecisionTree, sectionSyntax, loweredLabel);
}
}
}
if (defaultLabel != null && !loweredDecisionTree.MatchIsComplete)
{
Add(loweredDecisionTree, (e, t) => new DecisionTree.Guarded(
expression: loweredExpression,
type: loweredExpression.Type,
bindings: default,
/// <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()));
}
/// <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()));
}
private BoundPatternSwitchLabel BindPatternSwitchSectionLabel(
Binder sectionBinder, BoundExpression boundSwitchExpression, SwitchLabelSyntax node, LabelSymbol label, ref BoundPatternSwitchLabel defaultLabel, DiagnosticBag diagnostics)
{
switch (node.Kind())
{
case SyntaxKind.CaseSwitchLabel:
{
var caseLabelSyntax = (CaseSwitchLabelSyntax)node;
bool wasExpression;
var pattern = sectionBinder.BindConstantPattern(
node, boundSwitchExpression, boundSwitchExpression.Type, caseLabelSyntax.Value, node.HasErrors, diagnostics, out wasExpression, wasSwitchCase: true);
bool hasErrors = pattern.HasErrors;
var constantValue = pattern.ConstantValue;
if (!hasErrors &&
(object)constantValue != null &&
pattern.Value.Type == SwitchGoverningType &&
this.FindMatchingSwitchCaseLabel(constantValue, caseLabelSyntax) != label)
{
diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, pattern.ConstantValue.GetValueToDisplay() ?? label.Name);
hasErrors = true;
}
if (caseLabelSyntax.Value.Kind() == SyntaxKind.DefaultLiteralExpression)
{
diagnostics.Add(ErrorCode.WRN_DefaultInSwitch, caseLabelSyntax.Value.Location);
}
// Until we've determined whether or not the switch label is reachable, we assume it
// is. The caller updates isReachable after determining if the label is subsumed.
const bool isReachable = true;
return(new BoundPatternSwitchLabel(node, label, pattern, null, isReachable, hasErrors));
}
case SyntaxKind.DefaultSwitchLabel:
{
var defaultLabelSyntax = (DefaultSwitchLabelSyntax)node;
var pattern = new BoundWildcardPattern(node);
bool hasErrors = pattern.HasErrors;
if (defaultLabel != null)
{
diagnostics.Add(ErrorCode.ERR_DuplicateCaseLabel, node.Location, label.Name);
hasErrors = true;
}
// We always treat the default label as reachable, even if the switch is complete.
const bool isReachable = true;
// Note that this is semantically last! The caller will place it in the decision tree
// in the final position.
defaultLabel = new BoundPatternSwitchLabel(node, label, pattern, null, isReachable, hasErrors);
return(defaultLabel);
}
case SyntaxKind.CasePatternSwitchLabel:
{
var matchLabelSyntax = (CasePatternSwitchLabelSyntax)node;
var pattern = sectionBinder.BindPattern(
matchLabelSyntax.Pattern, boundSwitchExpression, boundSwitchExpression.Type, node.HasErrors, diagnostics, wasSwitchCase: true);
return(new BoundPatternSwitchLabel(node, label, pattern,
matchLabelSyntax.WhenClause != null ? sectionBinder.BindBooleanExpression(matchLabelSyntax.WhenClause.Condition, diagnostics) : null,
true, node.HasErrors));
}
default:
throw ExceptionUtilities.UnexpectedValue(node);
}
}
private BoundPatternSwitchLabel LowerSwitchLabel(BoundPatternSwitchLabel label)
{
return(label.Update(label.Label, _localRewriter.LowerPattern(label.Pattern), _localRewriter.VisitExpression(label.Guard), label.IsReachable));
}
private ImmutableArray <BoundPatternSwitchSection> BindPatternSwitchSections(BoundExpression boundSwitchExpression, SyntaxList <SwitchSectionSyntax> sections, Binder originalBinder, out BoundPatternSwitchLabel defaultLabel, DiagnosticBag diagnostics)
{
defaultLabel = null;
// Bind match sections
var boundPatternSwitchSectionsBuilder = ArrayBuilder <BoundPatternSwitchSection> .GetInstance();
foreach (var sectionSyntax in sections)
{
boundPatternSwitchSectionsBuilder.Add(BindPatternSwitchSection(boundSwitchExpression, sectionSyntax, originalBinder, ref defaultLabel, diagnostics));
}
return(boundPatternSwitchSectionsBuilder.ToImmutableAndFree());
}
internal DecisionTree ComputeDecisionTree()
{
Debug.Assert(_section == null);
var expression = _switchStatement.Expression;
if (expression.ConstantValue == null && expression.Kind != BoundKind.Local)
{
// unless the expression is simple enough, copy it into a local
var localSymbol = new SynthesizedLocal(_enclosingSymbol as MethodSymbol, expression.Type, SynthesizedLocalKind.PatternMatchingTemp, _switchStatement.Syntax, false, RefKind.None);
expression = new BoundLocal(expression.Syntax, localSymbol, null, expression.Type);
}
var result = DecisionTree.Create(_switchStatement.Expression, _switchStatement.Expression.Type, _enclosingSymbol);
var subsumptionTree = DecisionTree.Create(_switchStatement.Expression, _switchStatement.Expression.Type, _enclosingSymbol);
BoundPatternSwitchLabel defaultLabel = null;
BoundPatternSwitchSection defaultSection = null;
foreach (var section in _switchStatement.SwitchSections)
{
this._section = section;
foreach (var label in section.SwitchLabels)
{
if (label.Syntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
if (defaultLabel != null)
{
// duplicate switch label will have been reported during initial binding.
}
else
{
defaultLabel = label;
defaultSection = section;
}
}
else
{
this._syntax = label.Syntax;
// For purposes of subsumption, we do not take into consideration the value
// of the input expression. Therefore we consider null possible if the type permits.
var subsumedErrorCode = CheckSubsumed(label.Pattern, subsumptionTree, inputCouldBeNull: true);
if (subsumedErrorCode != 0 && subsumedErrorCode != ErrorCode.ERR_NoImplicitConvCast)
{
if (!label.HasErrors)
{
_diagnostics.Add(subsumedErrorCode, label.Pattern.Syntax.Location);
}
}
else
{
AddToDecisionTree(result, label);
if (label.Guard == null || label.Guard.ConstantValue == ConstantValue.True)
{
// Only unconditional switch labels contribute to subsumption
AddToDecisionTree(subsumptionTree, label);
}
}
}
}
}
if (defaultLabel != null)
{
Add(result, (e, t) => new DecisionTree.Guarded(_switchStatement.Expression, _switchStatement.Expression.Type, default(ImmutableArray <KeyValuePair <BoundExpression, BoundExpression> >), defaultSection, null, defaultLabel));
}
return(result);
}
/// <summary>
/// Add the case label to the subsumption tree. Return true if the label is reachable
/// given the expression and previously added labels. `valueMatched` is set to true
/// if and only if the label is a reachable unconditional (no when clause) constant pattern
/// whose value is the same as the input expression's constant value, and false otherwise.
/// </summary>
internal bool AddLabel(BoundPatternSwitchLabel label, DiagnosticBag diagnostics, out bool valueMatched)
{
// Use site diagnostics are reported (and cleared) by this method.
// So they should be empty when we start.
Debug.Assert(_useSiteDiagnostics.Count == 0);
valueMatched = false;
if (label.Syntax.Kind() == SyntaxKind.DefaultSwitchLabel)
{
// the default case label is always considered reachable.
return(true);
}
try
{
// For purposes of subsumption, we do not take into consideration the value
// of the input expression. Therefore we consider null possible if the type permits.
Syntax = label.Syntax;
var subsumedErrorCode = CheckSubsumed(label.Pattern, _subsumptionTree, inputCouldBeNull: true);
if (subsumedErrorCode != 0 && subsumedErrorCode != ErrorCode.ERR_NoImplicitConvCast)
{
if (!label.HasErrors)
{
diagnostics.Add(subsumedErrorCode, label.Pattern.Syntax.Location);
}
return(false);
}
var guardAlwaysSatisfied = label.Guard == null || label.Guard.ConstantValue == ConstantValue.True;
if (guardAlwaysSatisfied)
{
// Only unconditional switch labels contribute to subsumption
if (AddToDecisionTree(_subsumptionTree, null, label) == null)
{
return(false);
}
}
// For a constant switch, a constant label is only reachable if the value is equal.
var patternConstant = (label.Pattern as BoundConstantPattern)?.ConstantValue;
if (this._subsumptionTree.Expression.ConstantValue == null ||
patternConstant == null)
{
// either the input or the pattern wasn't a constant, so they might match.
return(true);
}
// If not subsumed, the label is considered reachable unless its constant value is
// distinct from the constant value of the input expression.
if (this._subsumptionTree.Expression.ConstantValue.Equals(patternConstant))
{
valueMatched = guardAlwaysSatisfied;
return(true);
}
return(false);
}
finally
{
// report the use-site diagnostics
diagnostics.Add(label.Syntax.Location, _useSiteDiagnostics);
_useSiteDiagnostics.Clear();
}
}