// 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.Collections.Immutable;
using System.Linq;
using System.Linq.Expressions;
using System.Threading;
using Microsoft.CodeAnalysis.CodeStyle;
using Microsoft.CodeAnalysis.CSharp.CodeStyle;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.LanguageService;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Diagnostics;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
namespace Microsoft.CodeAnalysis.CSharp.InlineDeclaration;
/// <summary>
/// Looks for code of the form:
///
/// int i;
/// if (int.TryParse(s, out i)) { }
///
/// And offers to convert it to:
///
/// if (int.TryParse(s, out var i)) { } or
/// if (int.TryParse(s, out int i)) { } or
///
/// </summary>
[DiagnosticAnalyzer(LanguageNames.CSharp)]
internal sealed class CSharpInlineDeclarationDiagnosticAnalyzer()
: AbstractBuiltInCodeStyleDiagnosticAnalyzer(IDEDiagnosticIds.InlineDeclarationDiagnosticId,
EnforceOnBuildValues.InlineDeclaration,
CSharpCodeStyleOptions.PreferInlinedVariableDeclaration,
new LocalizableResourceString(nameof(CSharpAnalyzersResources.Inline_variable_declaration), CSharpAnalyzersResources.ResourceManager, typeof(CSharpAnalyzersResources)),
new LocalizableResourceString(nameof(CSharpAnalyzersResources.Variable_declaration_can_be_inlined), CSharpAnalyzersResources.ResourceManager, typeof(CSharpAnalyzersResources)))
{
private const string CS0165 = nameof(CS0165); // Use of unassigned local variable 's'
public override DiagnosticAnalyzerCategory GetAnalyzerCategory()
=> DiagnosticAnalyzerCategory.SemanticSpanAnalysis;
protected override void InitializeWorker(AnalysisContext context)
{
context.RegisterCompilationStartAction(compilationContext =>
{
var compilation = compilationContext.Compilation;
var expressionType = compilation.GetTypeByMetadataName(typeof(Expression<>).FullName!);
// We wrap the SyntaxNodeAction within a CodeBlockStartAction, which allows us to
// get callbacks for Argument nodes, but analyze nodes across the entire code block
// and eventually report a diagnostic on the local declaration node.
// Without the containing CodeBlockStartAction, our reported diagnostic would be classified
// as a non-local diagnostic and would not participate in lightbulb for computing code fixes.
compilationContext.RegisterCodeBlockStartAction<SyntaxKind>(blockStartContext =>
blockStartContext.RegisterSyntaxNodeAction(
syntaxContext => AnalyzeSyntaxNode(syntaxContext, expressionType), SyntaxKind.Argument));
});
}
private void AnalyzeSyntaxNode(SyntaxNodeAnalysisContext context, INamedTypeSymbol? expressionType)
{
var syntaxTree = context.Node.SyntaxTree;
var csOptions = (CSharpParseOptions)syntaxTree.Options;
if (csOptions.LanguageVersion < LanguageVersion.CSharp7)
{
// out-vars are not supported prior to C# 7.0.
return;
}
var option = context.GetCSharpAnalyzerOptions().PreferInlinedVariableDeclaration;
if (!option.Value || ShouldSkipAnalysis(context, option.Notification))
{
// Don't bother doing any work if the user doesn't even have this preference set.
return;
}
var argumentNode = (ArgumentSyntax)context.Node;
if (argumentNode.RefOrOutKeyword.Kind() != SyntaxKind.OutKeyword)
{
// Immediately bail if this is not an out-argument. If it's not an out-argument
// we clearly can't convert it to be an out-variable-declaration.
return;
}
var argumentExpression = argumentNode.Expression;
if (argumentExpression is not IdentifierNameSyntax identifierName)
{
// has to be exactly the form "out i". i.e. "out this.i" or "out v[i]" are legal
// cases for out-arguments, but could not be converted to an out-variable-declaration.
return;
}
if (argumentNode.Parent is not ArgumentListSyntax argumentList)
{
return;
}
var invocationOrCreation = argumentList.Parent;
if (invocationOrCreation?.Kind() is not SyntaxKind.InvocationExpression and not SyntaxKind.ObjectCreationExpression)
{
// Out-variables are only legal with invocations and object creations.
// If we don't have one of those bail. Note: we need hte parent to be
// one of these forms so we can accurately verify that inlining the
// variable doesn't change semantics.
return;
}
// Don't offer to inline variables named "_". It can cause is to create a discard symbol
// which would cause a break.
if (identifierName.Identifier.ValueText == "_")
{
return;
}
var containingStatement = argumentExpression.FirstAncestorOrSelf<StatementSyntax>();
if (containingStatement == null)
{
return;
}
var cancellationToken = context.CancellationToken;
var semanticModel = context.SemanticModel;
if (semanticModel.GetSymbolInfo(argumentExpression, cancellationToken).Symbol is not ILocalSymbol outLocalSymbol)
{
// The out-argument wasn't referencing a local. So we don't have an local
// declaration that we can attempt to inline here.
return;
}
// Ensure that the local-symbol actually belongs to LocalDeclarationStatement.
// Trying to do things like inline a var-decl in a for-statement is just too
// esoteric and would make us have to write a lot more complex code to support
// that scenario.
var localReference = outLocalSymbol.DeclaringSyntaxReferences.FirstOrDefault();
if (localReference?.GetSyntax(cancellationToken) is not VariableDeclaratorSyntax localDeclarator)
{
return;
}
var localDeclaration = localDeclarator.Parent as VariableDeclarationSyntax;
if (localDeclaration?.Parent is not LocalDeclarationStatementSyntax localStatement)
{
return;
}
// Bail out early if the localDeclaration is outside the context's analysis span.
if (!context.ShouldAnalyzeSpan(localDeclaration.Span))
return;
if (localDeclarator.SpanStart >= argumentNode.SpanStart)
{
// We have an error situation where the local was declared after the out-var.
// Don't even bother offering anything here.
return;
}
// If the local has an initializer, only allow the refactoring if it is initialized
// with a simple literal or 'default' expression. i.e. it's ok to inline "var v = 0"
// since there are no side-effects of the initialization. However something like
// "var v = M()" should not be inlined as that could break program semantics.
if (localDeclarator.Initializer != null)
{
if (localDeclarator.Initializer.Value is not LiteralExpressionSyntax and
not DefaultExpressionSyntax)
{
return;
}
}
// Get the block that the local is scoped inside of. We'll search that block
// for references to the local to make sure that no reads/writes happen before
// the out-argument. If there are any reads/writes we can't inline as those
// accesses will become invalid.
var enclosingBlockOfLocalStatement = CSharpBlockFacts.Instance.GetImmediateParentExecutableBlockForStatement(localStatement);
if (enclosingBlockOfLocalStatement is null)
return;
if (argumentExpression.IsInExpressionTree(semanticModel, expressionType, cancellationToken))
{
// out-vars are not allowed inside expression-trees. So don't offer to
// fix if we're inside one.
return;
}
// Find the scope that the out-declaration variable will live in after we
// rewrite things.
var outArgumentScope = GetOutArgumentScope(argumentExpression);
if (outArgumentScope == null)
return;
if (!outLocalSymbol.CanSafelyMoveLocalToBlock(enclosingBlockOfLocalStatement, outArgumentScope))
{
return;
}
// Make sure that variable is not accessed outside of that scope.
var dataFlow = semanticModel.AnalyzeDataFlow(outArgumentScope);
if (dataFlow.ReadOutside.Contains(outLocalSymbol) || dataFlow.WrittenOutside.Contains(outLocalSymbol))
{
// The variable is read or written from outside the block that the new variable
// would be scoped in. This would cause a break.
//
// Note(cyrusn): We could still offer the refactoring, but just show an error in the
// preview in this case.
return;
}
// Make sure the variable isn't ever accessed before the usage in this out-var.
if (IsAccessed(semanticModel, outLocalSymbol, enclosingBlockOfLocalStatement,
localStatement, argumentNode, cancellationToken))
{
return;
}
// See if inlining this variable would make it so that some variables were no
// longer definitely assigned.
if (WouldCauseDefiniteAssignmentErrors(
semanticModel, localStatement, enclosingBlockOfLocalStatement, outLocalSymbol))
{
return;
}
// Collect some useful nodes for the fix provider to use so it doesn't have to
// find them again.
var allLocations = ImmutableArray.Create(
localDeclarator.GetLocation(),
identifierName.GetLocation(),
invocationOrCreation.GetLocation());
// If the local variable only has one declarator, then report the suggestion on the whole
// declaration. Otherwise, return the suggestion only on the single declarator.
var reportNode = localDeclaration.Variables.Count == 1
? (SyntaxNode)localDeclaration
: localDeclarator;
context.ReportDiagnostic(DiagnosticHelper.Create(
Descriptor,
reportNode.GetLocation(),
option.Notification,
context.Options,
additionalLocations: allLocations,
properties: null));
}
private static bool WouldCauseDefiniteAssignmentErrors(
SemanticModel semanticModel,
LocalDeclarationStatementSyntax localStatement,
SyntaxNode enclosingBlock,
ILocalSymbol outLocalSymbol)
{
// See if we have something like:
//
// int i = 0;
// if (Goo() || Bar(out i))
// {
// Console.WriteLine(i);
// }
//
// In this case, inlining the 'i' would cause it to longer be definitely
// assigned in the WriteLine invocation.
var nextStatement = localStatement.GetNextStatement();
Contract.ThrowIfNull(nextStatement);
var dataFlow = semanticModel.AnalyzeDataFlow(
nextStatement,
CSharpBlockFacts.Instance.GetExecutableBlockStatements(enclosingBlock).Last());
Contract.ThrowIfNull(dataFlow);
return dataFlow.DataFlowsIn.Contains(outLocalSymbol);
}
private static SyntaxNode? GetOutArgumentScope(SyntaxNode argumentExpression)
{
for (var current = argumentExpression; current != null; current = current.Parent)
{
// We were in a lambda. The lambda body will be the new scope of the out var.
if (current.Parent is LambdaExpressionSyntax lambda && current == lambda.Body)
return current;
// The arm of a switch expression is its own isolated scope.
if (current.Parent is SwitchExpressionArmSyntax switchArm && current == switchArm.Expression)
return current;
// Any loop construct defines a scope for out-variables, as well as each of the following:
// * Using statements
// * Fixed statements
// * Try statements (specifically for exception filters)
switch (current.Kind())
{
case SyntaxKind.WhileStatement:
case SyntaxKind.DoStatement:
case SyntaxKind.ForStatement:
case SyntaxKind.ForEachStatement:
case SyntaxKind.UsingStatement:
case SyntaxKind.FixedStatement:
case SyntaxKind.TryStatement:
return current;
}
if (current is StatementSyntax)
{
// We hit a statement containing the out-argument. Statements can have one of
// two forms. They're either parented by a block, or by another statement
// (i.e. they're an embedded statement). If we're parented by a block, then
// that block will be the scope of the new out-var.
//
// However, if our containing statement is not parented by a block, then that
// means we have something like:
//
// if (x)
// if (Try(out y))
//
// In this case, there is a 'virtual' block scope surrounding the embedded 'if'
// statement, and that will be the scope the out-var goes into.
return current.IsParentKind(SyntaxKind.Block)
? current.Parent
: current;
}
}
return null;
}
private static bool IsAccessed(
SemanticModel semanticModel,
ISymbol outSymbol,
SyntaxNode enclosingBlockOfLocalStatement,
LocalDeclarationStatementSyntax localStatement,
ArgumentSyntax argumentNode,
CancellationToken cancellationToken)
{
var localStatementStart = localStatement.Span.Start;
var argumentNodeStart = argumentNode.Span.Start;
var variableName = outSymbol.Name;
// Walk the block that the local is declared in looking for accesses.
// We can ignore anything prior to the actual local declaration point,
// and we only need to check up until we reach the out-argument.
foreach (var descendentNode in enclosingBlockOfLocalStatement.DescendantNodes())
{
var descendentStart = descendentNode.Span.Start;
if (descendentStart <= localStatementStart)
{
// This node is before the local declaration. Can ignore it entirely as it could
// not be an access to the local.
continue;
}
if (descendentStart >= argumentNodeStart)
{
// We reached the out-var. We can stop searching entirely.
break;
}
if (descendentNode is IdentifierNameSyntax identifierName)
{
// See if this looks like an accessor to the local variable syntactically.
if (identifierName.Identifier.ValueText == variableName)
{
// Confirm that it is a access of the local.
var symbol = semanticModel.GetSymbolInfo(identifierName, cancellationToken).Symbol;
if (outSymbol.Equals(symbol))
{
// We definitely accessed the local before the out-argument. We
// can't inline this local.
return true;
}
}
}
}
// No accesses detected
return false;
}
}