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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System;
using System.Collections.Immutable;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.ErrorReporting;
using Microsoft.CodeAnalysis.Host;
using Microsoft.CodeAnalysis.LanguageService;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;
namespace Microsoft.CodeAnalysis.ReassignedVariable
{
internal abstract class AbstractReassignedVariableService<
TParameterSyntax,
TVariableSyntax,
TSingleVariableDesignationSyntax,
TIdentifierNameSyntax>
: IReassignedVariableService
where TParameterSyntax : SyntaxNode
where TVariableSyntax : SyntaxNode
where TSingleVariableDesignationSyntax : SyntaxNode
where TIdentifierNameSyntax : SyntaxNode
{
protected abstract SyntaxNode GetParentScope(SyntaxNode localDeclaration);
protected abstract SyntaxNode GetMemberBlock(SyntaxNode methodOrPropertyDeclaration);
protected abstract bool HasInitializer(SyntaxNode variable);
protected abstract SyntaxToken GetIdentifierOfVariable(TVariableSyntax variable);
protected abstract SyntaxToken GetIdentifierOfSingleVariableDesignation(TSingleVariableDesignationSyntax variable);
public async Task<ImmutableArray<TextSpan>> GetLocationsAsync(
Document document, TextSpan span, CancellationToken cancellationToken)
{
var semanticFacts = document.GetRequiredLanguageService<ISemanticFactsService>();
var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
var root = await document.GetRequiredSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
using var _1 = PooledDictionary<ISymbol, bool>.GetInstance(out var symbolToIsReassigned);
using var _2 = ArrayBuilder<TextSpan>.GetInstance(out var result);
using var _3 = ArrayBuilder<SyntaxNode>.GetInstance(out var stack);
// Walk through all the nodes in the provided span. Directly analyze local or parameter declaration. And
// also analyze any identifiers which might be reference to locals or parameters. Note that we might hit
// locals/parameters without any references in the span, or references that don't have the declarations in
// the span
stack.Add(root.FindNode(span));
// Use a stack so we don't blow out the stack with recursion.
while (stack.Count > 0)
{
var current = stack.Last();
stack.RemoveLast();
if (current.Span.IntersectsWith(span))
{
ProcessNode(current);
foreach (var child in current.ChildNodesAndTokens())
{
if (child.IsNode)
stack.Add(child.AsNode()!);
}
}
}
result.RemoveDuplicates();
return result.ToImmutable();
void ProcessNode(SyntaxNode node)
{
switch (node)
{
case TIdentifierNameSyntax identifier:
ProcessIdentifier(identifier);
break;
case TParameterSyntax parameter:
ProcessParameter(parameter);
break;
case TVariableSyntax variable:
ProcessVariable(variable);
break;
case TSingleVariableDesignationSyntax designation:
ProcessSingleVariableDesignation(designation);
break;
}
}
void ProcessIdentifier(TIdentifierNameSyntax identifier)
{
// Don't bother even looking at identifiers that aren't standalone (i.e. they're not on the left of some
// expression). These could not refer to locals or fields.
if (syntaxFacts.GetStandaloneExpression(identifier) != identifier)
return;
var symbol = semanticModel.GetSymbolInfo(identifier, cancellationToken).Symbol;
if (IsSymbolReassigned(symbol))
result.Add(identifier.Span);
}
void ProcessParameter(TParameterSyntax parameterSyntax)
{
var parameter = semanticModel.GetDeclaredSymbol(parameterSyntax, cancellationToken) as IParameterSymbol;
if (IsSymbolReassigned(parameter))
result.Add(syntaxFacts.GetIdentifierOfParameter(parameterSyntax).Span);
}
void ProcessVariable(TVariableSyntax variable)
{
var local = semanticModel.GetDeclaredSymbol(variable, cancellationToken) as ILocalSymbol;
if (IsSymbolReassigned(local))
result.Add(GetIdentifierOfVariable(variable).Span);
}
void ProcessSingleVariableDesignation(TSingleVariableDesignationSyntax designation)
{
var local = semanticModel.GetDeclaredSymbol(designation, cancellationToken) as ILocalSymbol;
if (IsSymbolReassigned(local))
result.Add(GetIdentifierOfSingleVariableDesignation(designation).Span);
}
bool IsSymbolReassigned([NotNullWhen(true)] ISymbol? symbol)
{
// Note: we don't need to test range variables, as they are never reassignable.
if (symbol is not IParameterSymbol and not ILocalSymbol)
return false;
if (!symbolToIsReassigned.TryGetValue(symbol, out var reassignedResult))
{
reassignedResult = symbol is IParameterSymbol parameter
? ComputeParameterIsAssigned(parameter)
: ComputeLocalIsAssigned((ILocalSymbol)symbol);
symbolToIsReassigned[symbol] = reassignedResult;
}
return reassignedResult;
}
bool ComputeParameterIsAssigned(IParameterSymbol parameter)
{
if (!TryGetParameterLocation(parameter, out var parameterLocation))
return false;
var methodOrProperty = parameter.ContainingSymbol;
// If we're on an accessor parameter. Map up to the matching parameter for the property/indexer.
if (methodOrProperty is IMethodSymbol { MethodKind: MethodKind.PropertyGet or MethodKind.PropertySet } method)
methodOrProperty = method.AssociatedSymbol as IPropertySymbol;
if (methodOrProperty is not IMethodSymbol and not IPropertySymbol)
return false;
if (methodOrProperty.DeclaringSyntaxReferences.Length == 0)
return false;
// Be resilient to cases where the parameter might have multiple locations. This
// should not normally happen, but we want to be resilient in case it occurs in
// error scenarios.
var methodOrPropertyDeclaration = methodOrProperty.DeclaringSyntaxReferences.First().GetSyntax(cancellationToken);
if (methodOrPropertyDeclaration.SyntaxTree != semanticModel.SyntaxTree)
return false;
// All parameters (except for 'out' parameters), come in definitely assigned.
return AnalyzePotentialMatches(
parameter,
parameterLocation,
symbolIsDefinitelyAssigned: parameter.RefKind != RefKind.Out,
GetMemberBlock(methodOrPropertyDeclaration));
}
bool TryGetParameterLocation(IParameterSymbol parameter, out TextSpan location)
{
// Be resilient to cases where the parameter might have multiple locations. This
// should not normally happen, but we want to be resilient in case it occurs in
// error scenarios.
if (parameter.Locations.Length > 0)
{
var parameterLocation = parameter.Locations[0];
if (parameterLocation.SourceTree == semanticModel.SyntaxTree)
{
location = parameterLocation.SourceSpan;
return true;
}
}
else if (parameter.ContainingSymbol.Name == WellKnownMemberNames.TopLevelStatementsEntryPointMethodName)
{
// If this is a parameter of the top-level-main function, then the entire span of the compilation
// unit is what we need to examine.
location = default;
return true;
}
location = default;
return false;
}
bool ComputeLocalIsAssigned(ILocalSymbol local)
{
if (local.DeclaringSyntaxReferences.Length == 0)
return false;
var localDeclaration = local.DeclaringSyntaxReferences
.Select(r => r.GetSyntax(cancellationToken))
.Where(s => s.SyntaxTree == semanticModel.SyntaxTree)
.FirstOrDefault();
if (localDeclaration == null)
{
FatalError.ReportAndCatch(new InvalidOperationException("Local did not come from same file that we were analyzing?"));
return false;
}
// A local is definitely assigned during analysis if it had an initializer.
return AnalyzePotentialMatches(
local,
localDeclaration.Span,
symbolIsDefinitelyAssigned: HasInitializer(localDeclaration),
GetParentScope(localDeclaration));
}
bool AnalyzePotentialMatches(
ISymbol localOrParameter,
TextSpan localOrParameterDeclarationSpan,
bool symbolIsDefinitelyAssigned,
SyntaxNode parentScope)
{
// Now, walk the scope, looking for all usages of the local. See if any are a reassignment.
using var _ = ArrayBuilder<SyntaxNode>.GetInstance(out var stack);
stack.Push(parentScope);
while (stack.Count != 0)
{
var current = stack.Last();
stack.RemoveLast();
foreach (var child in current.ChildNodesAndTokens())
{
if (child.IsNode)
stack.Add(child.AsNode()!);
}
// Ignore any nodes before the decl.
if (current.SpanStart <= localOrParameterDeclarationSpan.Start)
continue;
// Only examine identifiers.
if (current is not TIdentifierNameSyntax id)
continue;
// Ignore identifiers that don't match the local name.
var idToken = syntaxFacts.GetIdentifierOfSimpleName(id);
if (!syntaxFacts.StringComparer.Equals(idToken.ValueText, localOrParameter.Name))
continue;
// Ignore identifiers that bind to another symbol.
var symbol = semanticModel.GetSymbolInfo(id, cancellationToken).Symbol;
if (!AreEquivalent(localOrParameter, symbol))
continue;
// Ok, we have a reference to the local. See if it was assigned on entry. If not, we don't care
// about this reference. As an assignment here doesn't mean it was reassigned.
//
// If we can statically tell it was definitely assigned, skip the more expensive dataflow check.
if (!symbolIsDefinitelyAssigned)
{
var dataFlow = semanticModel.AnalyzeDataFlow(id);
if (!DefinitelyAssignedOnEntry(dataFlow, localOrParameter))
continue;
}
// This was a variable that was already assigned prior to this location. See if this location is
// considered a write.
if (semanticFacts.IsWrittenTo(semanticModel, id, cancellationToken))
return true;
}
return false;
}
bool AreEquivalent(ISymbol localOrParameter, ISymbol? symbol)
{
if (symbol == null)
return false;
if (localOrParameter.Equals(symbol))
return true;
if (localOrParameter.Kind != symbol.Kind)
return false;
// Special case for property parameters. When we bind to references, we'll bind to the parameters on
// the accessor methods. We need to map these back to the property parameter to see if we have a hit.
if (localOrParameter is IParameterSymbol { ContainingSymbol: IPropertySymbol property } parameter)
{
var getParameter = property.GetMethod?.Parameters[parameter.Ordinal];
var setParameter = property.SetMethod?.Parameters[parameter.Ordinal];
return Equals(getParameter, symbol) || Equals(setParameter, symbol);
}
return false;
}
bool DefinitelyAssignedOnEntry(DataFlowAnalysis? analysis, ISymbol? localOrParameter)
{
if (analysis == null)
return false;
if (localOrParameter == null)
return false;
if (analysis.DefinitelyAssignedOnEntry.Contains(localOrParameter))
return true;
// Special case for property parameters. When we bind to references, we'll bind to the parameters on
// the accessor methods. We need to map these back to the property parameter to see if we have a hit.
if (localOrParameter is IParameterSymbol { ContainingSymbol: IPropertySymbol property } parameter)
{
var getParameter = property.GetMethod?.Parameters[parameter.Ordinal];
var setParameter = property.SetMethod?.Parameters[parameter.Ordinal];
return DefinitelyAssignedOnEntry(analysis, getParameter) ||
DefinitelyAssignedOnEntry(analysis, setParameter);
}
return false;
}
}
}
}
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