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)); } }