private async Task FixAllValueAssignedIsUnusedDiagnosticsAsync(
IOrderedEnumerable <Diagnostic> diagnostics,
Document document,
SemanticModel semanticModel,
SyntaxNode root,
SyntaxNode containingMemberDeclaration,
UnusedValuePreference preference,
bool removeAssignments,
UniqueVariableNameGenerator nameGenerator,
SyntaxEditor editor,
ISyntaxFactsService syntaxFacts,
CancellationToken cancellationToken)
{
// This method applies the code fix for diagnostics reported for unused value assignments to local/parameter.
// The actual code fix depends on whether or not the right hand side of the assignment has side effects.
// For example, if the right hand side is a constant or a reference to a local/parameter, then it has no side effects.
// The lack of side effects is indicated by the "removeAssignments" parameter for this function.
// If the right hand side has no side effects, then we can replace the assignments with variable declarations that have no initializer
// or completely remove the statement.
// If the right hand side does have side effects, we replace the identifier token for unused value assignment with
// a new identifier token (either discard '_' or new unused local variable name).
// For both the above cases, if the original diagnostic was reported on a local declaration, i.e. redundant initialization
// at declaration, then we also add a new variable declaration statement without initializer for this local.
var nodeReplacementMap = PooledDictionary <SyntaxNode, SyntaxNode> .GetInstance();
var nodesToRemove = PooledHashSet <SyntaxNode> .GetInstance();
var candidateDeclarationStatementsForRemoval = PooledHashSet <TLocalDeclarationStatementSyntax> .GetInstance();
var hasAnyUnusedLocalAssignment = false;
try
{
foreach (var(node, isUnusedLocalAssignment) in GetNodesToFix())
{
hasAnyUnusedLocalAssignment |= isUnusedLocalAssignment;
var declaredLocal = semanticModel.GetDeclaredSymbol(node, cancellationToken) as ILocalSymbol;
if (declaredLocal == null && node.Parent is TCatchStatementSyntax)
{
declaredLocal = semanticModel.GetDeclaredSymbol(node.Parent, cancellationToken) as ILocalSymbol;
}
string newLocalNameOpt = null;
if (removeAssignments)
{
// Removable assignment or initialization, such that right hand side has no side effects.
if (declaredLocal != null)
{
// Redundant initialization.
// For example, "int a = 0;"
var variableDeclarator = node.FirstAncestorOrSelf <TVariableDeclarationSyntax>();
Debug.Assert(variableDeclarator != null);
nodesToRemove.Add(variableDeclarator);
// Local declaration statement containing the declarator might be a candidate for removal if all its variables get marked for removal.
candidateDeclarationStatementsForRemoval.Add(variableDeclarator.GetAncestor <TLocalDeclarationStatementSyntax>());
}
else
{
// Redundant assignment or increment/decrement.
if (syntaxFacts.IsOperandOfIncrementOrDecrementExpression(node))
{
// For example, C# increment operation "a++;"
Debug.Assert(node.Parent.Parent is TExpressionStatementSyntax);
nodesToRemove.Add(node.Parent.Parent);
}
else
{
Debug.Assert(syntaxFacts.IsLeftSideOfAnyAssignment(node));
if (node.Parent is TStatementSyntax)
{
// For example, VB simple assignment statement "a = 0"
nodesToRemove.Add(node.Parent);
}
else if (node.Parent is TExpressionSyntax && node.Parent.Parent is TExpressionStatementSyntax)
{
// For example, C# simple assignment statement "a = 0;"
nodesToRemove.Add(node.Parent.Parent);
}
else
{
// For example, C# nested assignment statement "a = b = 0;", where assignment to 'b' is redundant.
// We replace the node with "a = 0;"
nodeReplacementMap.Add(node.Parent, syntaxFacts.GetRightHandSideOfAssignment(node.Parent));
}
}
}
}
else
{
// Value initialization/assignment where the right hand side may have side effects,
// and hence needs to be preserved in fixed code.
// For example, "x = MethodCall();" is replaced with "_ = MethodCall();" or "var unused = MethodCall();"
// Replace the flagged variable's indentifier token with new named, based on user's preference.
var newNameToken = preference == UnusedValuePreference.DiscardVariable
? editor.Generator.Identifier(AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.DiscardVariableName)
: nameGenerator.GenerateUniqueNameAtSpanStart(node);
newLocalNameOpt = newNameToken.ValueText;
var newNameNode = TryUpdateNameForFlaggedNode(node, newNameToken);
if (newNameNode == null)
{
continue;
}
// Is this is compound assignment?
if (syntaxFacts.IsLeftSideOfAnyAssignment(node) && !syntaxFacts.IsLeftSideOfAssignment(node))
{
// Compound assignment is changed to simple assignment.
// For example, "x += MethodCall();", where assignment to 'x' is redundant
// is replaced with "_ = MethodCall();" or "var unused = MethodCall();"
nodeReplacementMap.Add(node.Parent, editor.Generator.AssignmentStatement(newNameNode, syntaxFacts.GetRightHandSideOfAssignment(node.Parent)));
}
else
{
nodeReplacementMap.Add(node, newNameNode);
}
}
if (declaredLocal != null)
{
// We have a dead initialization for a local declaration.
// Introduce a new local declaration statement without an initializer for this local.
var declarationStatement = CreateLocalDeclarationStatement(declaredLocal.Type, declaredLocal.Name);
if (isUnusedLocalAssignment)
{
declarationStatement = declarationStatement.WithAdditionalAnnotations(s_unusedLocalDeclarationAnnotation);
}
InsertLocalDeclarationStatement(declarationStatement, node);
}
else
{
// We have a dead assignment to a local/parameter, which is not at the declaration site.
// Create a new local declaration for the unused local if both following conditions are met:
// 1. User prefers unused local variables for unused value assignment AND
// 2. Assignment value has side effects and hence cannot be removed.
if (preference == UnusedValuePreference.UnusedLocalVariable && !removeAssignments)
{
var type = semanticModel.GetTypeInfo(node, cancellationToken).Type;
Debug.Assert(type != null);
Debug.Assert(newLocalNameOpt != null);
var declarationStatement = CreateLocalDeclarationStatement(type, newLocalNameOpt);
InsertLocalDeclarationStatement(declarationStatement, node);
}
}
}
// Process candidate declaration statements for removal.
foreach (var localDeclarationStatement in candidateDeclarationStatementsForRemoval)
{
// If all the variable declarators for the local declaration statement are being removed,
// we can remove the entire local declaration statement.
if (ShouldRemoveStatement(localDeclarationStatement, out var variables))
{
nodesToRemove.Add(localDeclarationStatement);
}
}
if (hasAnyUnusedLocalAssignment)
{
// Local declaration statements with no initializer, but non-zero references are candidates for removal
// if the code fix removes all these references.
// We annotate such declaration statements with no initializer abd non-zero references here
// and remove them in post process document pass later, if the code fix did remove all these references.
foreach (var localDeclarationStatement in containingMemberDeclaration.DescendantNodes().OfType <TLocalDeclarationStatementSyntax>())
{
var variables = syntaxFacts.GetVariablesOfLocalDeclarationStatement(localDeclarationStatement);
if (syntaxFacts.GetInitializerOfVariableDeclaration(variables) == null &&
!(await IsLocalDeclarationWithNoReferencesAsync(localDeclarationStatement, document, cancellationToken).ConfigureAwait(false)))
{
nodeReplacementMap.Add(localDeclarationStatement, localDeclarationStatement.WithAdditionalAnnotations(s_existingLocalDeclarationWithoutInitializerAnnotation));
}
}
}
foreach (var node in nodesToRemove)
{
editor.RemoveNode(node, SyntaxGenerator.DefaultRemoveOptions | SyntaxRemoveOptions.KeepLeadingTrivia);
}
foreach (var kvp in nodeReplacementMap)
{
editor.ReplaceNode(kvp.Key, kvp.Value.WithAdditionalAnnotations(Formatter.Annotation));
}
}
finally
{
nodeReplacementMap.Free();
nodesToRemove.Free();
}
return;
// Local functions.
IEnumerable <(SyntaxNode node, bool isUnusedLocalAssignment)> GetNodesToFix()
{
foreach (var diagnostic in diagnostics)
{
var node = root.FindNode(diagnostic.Location.SourceSpan, getInnermostNodeForTie: true);
var isUnusedLocalAssignment = AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.GetIsUnusedLocalDiagnostic(diagnostic);
yield return(node, isUnusedLocalAssignment);
}
}
// Mark generated local declaration statement with:
// 1. "s_newLocalDeclarationAnnotation" for post processing in "MoveNewLocalDeclarationsNearReference" below.
// 2. Simplifier annotation so that 'var'/explicit type is correctly added based on user options.
TLocalDeclarationStatementSyntax CreateLocalDeclarationStatement(ITypeSymbol type, string name)
=> (TLocalDeclarationStatementSyntax)editor.Generator.LocalDeclarationStatement(type, name)
.WithLeadingTrivia(editor.Generator.ElasticCarriageReturnLineFeed)
.WithAdditionalAnnotations(s_newLocalDeclarationStatementAnnotation, Simplifier.Annotation);
void InsertLocalDeclarationStatement(TLocalDeclarationStatementSyntax declarationStatement, SyntaxNode node)
{
// Find the correct place to insert the given declaration statement based on the node's ancestors.
var insertionNode = node.FirstAncestorOrSelf <SyntaxNode>(n => n.Parent is TSwitchCaseBlockSyntax ||
syntaxFacts.IsExecutableBlock(n.Parent) &&
!(n is TCatchStatementSyntax) &&
!(n is TCatchBlockSyntax));
if (insertionNode is TSwitchCaseLabelOrClauseSyntax)
{
InsertAtStartOfSwitchCaseBlockForDeclarationInCaseLabelOrClause(insertionNode.GetAncestor <TSwitchCaseBlockSyntax>(), editor, declarationStatement);
}
else if (insertionNode is TStatementSyntax)
{
editor.InsertBefore(insertionNode, declarationStatement);
}
}
bool ShouldRemoveStatement(TLocalDeclarationStatementSyntax localDeclarationStatement, out SyntaxNode variables)
{
Debug.Assert(removeAssignments);
// We should remove the entire local declaration statement if all its variables are marked for removal.
variables = syntaxFacts.GetVariablesOfLocalDeclarationStatement(localDeclarationStatement);
return(nodesToRemove.Contains(variables));
}
}