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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.Collections.Immutable;
using System.Diagnostics.CodeAnalysis;
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.Operations;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Text;
namespace Microsoft.CodeAnalysis.CSharp.UseIndexOrRangeOperator;
using static Helpers;
/// <summary>
/// <para>Analyzer that looks for several variants of code like <c>s.Slice(start, end - start)</c> and offers to update
/// to <c>s[start..end]</c> or <c>s.Slice(start..end)</c>. In order to convert to the indexer, the type being called on
/// needs a slice-like method that takes two ints, and returns an instance of the same type. It also needs a
/// <c>Length</c>/<c>Count</c> property, as well as an indexer that takes a <see cref="T:System.Range"/> instance. In
/// order to convert between methods, there need to be two overloads that are equivalent except that one takes two ints,
/// and the other takes a <see cref="T:System.Range"/>.</para>
///
/// <para>It is assumed that if the type follows this shape that it is well behaved and that this transformation will
/// preserve semantics. If this assumption is not good in practice, we could always limit the feature to only work on
/// an allow list of known safe types.</para>
/// </summary>
[DiagnosticAnalyzer(LanguageNames.CSharp)]
[SuppressMessage("Documentation", "CA1200:Avoid using cref tags with a prefix", Justification = "Required to avoid ambiguous reference warnings.")]
internal sealed partial class CSharpUseRangeOperatorDiagnosticAnalyzer()
: AbstractBuiltInCodeStyleDiagnosticAnalyzer(
IDEDiagnosticIds.UseRangeOperatorDiagnosticId,
EnforceOnBuildValues.UseRangeOperator,
CSharpCodeStyleOptions.PreferRangeOperator,
new LocalizableResourceString(nameof(CSharpAnalyzersResources.Use_range_operator), CSharpAnalyzersResources.ResourceManager, typeof(CSharpAnalyzersResources)),
new LocalizableResourceString(nameof(CSharpAnalyzersResources._0_can_be_simplified), CSharpAnalyzersResources.ResourceManager, typeof(CSharpAnalyzersResources)))
{
// public const string UseIndexer = nameof(UseIndexer);
public const string ComputedRange = nameof(ComputedRange);
public const string ConstantRange = nameof(ConstantRange);
public override DiagnosticAnalyzerCategory GetAnalyzerCategory() => DiagnosticAnalyzerCategory.SemanticSpanAnalysis;
protected override void InitializeWorker(AnalysisContext context)
{
context.RegisterCompilationStartAction(context =>
{
var compilation = context.Compilation;
// Check if we're at least on C# 8
if (compilation.LanguageVersion() < LanguageVersion.CSharp8)
return;
// We're going to be checking every invocation in the compilation. Cache information
// we compute in this object so we don't have to continually recompute it.
if (!InfoCache.TryCreate(compilation, out var infoCache))
return;
context.RegisterOperationAction(
context => AnalyzeInvocation(context, infoCache),
OperationKind.Invocation);
});
}
private void AnalyzeInvocation(OperationAnalysisContext context, InfoCache infoCache)
{
// Check if the user wants these operators.
var option = context.GetCSharpAnalyzerOptions().PreferRangeOperator;
if (!option.Value || ShouldSkipAnalysis(context, option.Notification))
return;
var operation = context.Operation;
var semanticModel = operation.SemanticModel;
Contract.ThrowIfNull(semanticModel);
var result = AnalyzeInvocation((IInvocationOperation)operation, infoCache);
if (result == null)
return;
if (CSharpSemanticFacts.Instance.IsInExpressionTree(semanticModel, operation.Syntax, infoCache.ExpressionOfTType, context.CancellationToken))
return;
context.ReportDiagnostic(CreateDiagnostic(result.Value, option.Notification, context.Options));
}
public static Result? AnalyzeInvocation(IInvocationOperation invocation, InfoCache infoCache)
{
// Validate we're on a piece of syntax we expect. While not necessary for analysis, we
// want to make sure we're on something the fixer will know how to actually fix.
if (invocation.Syntax is not InvocationExpressionSyntax invocationSyntax ||
invocationSyntax.ArgumentList is null)
{
return null;
}
// look for `s.Slice(e1, end - e2)` or `s.Slice(e1)`
if (invocation.Instance is null)
return null;
return invocation.Arguments.Length switch
{
1 => AnalyzeOneArgumentInvocation(invocation, infoCache, invocationSyntax),
2 => AnalyzeTwoArgumentInvocation(invocation, infoCache, invocationSyntax),
_ => null,
};
}
private static Result? AnalyzeOneArgumentInvocation(
IInvocationOperation invocation,
InfoCache infoCache,
InvocationExpressionSyntax invocationSyntax)
{
var targetMethod = invocation.TargetMethod;
// We are dealing with a call like `.Substring(expr)`. Ensure that there is an overload with signature like
// `Substring(int start, int length)` and there is a suitable indexer to replace this with `[expr..]`.
if (!infoCache.TryGetMemberInfoOneArgument(targetMethod, out var memberInfo))
return null;
var startOperation = invocation.Arguments[0].Value;
return new Result(
ResultKind.Computed,
invocation,
invocationSyntax,
targetMethod,
memberInfo,
op1: startOperation,
op2: null); // The range will run to the end.
}
private static Result? AnalyzeTwoArgumentInvocation(
IInvocationOperation invocation,
InfoCache infoCache,
InvocationExpressionSyntax invocationSyntax)
{
Contract.ThrowIfNull(invocation.Instance);
// See if the call is to something slice-like.
var targetMethod = invocation.TargetMethod;
if (targetMethod == null)
return null;
if (IsStringRemoveMethod(targetMethod) &&
infoCache.TryGetMemberInfo(targetMethod, out var memberInfo))
{
return AnalyzeTwoArgumentStringRemoveInvocation(invocation, infoCache, invocationSyntax, targetMethod, memberInfo);
}
return AnalyzeTwoArgumentSubtractionInvocation(invocation, infoCache, invocationSyntax, targetMethod) ??
AnalyzeTwoArgumentFromStartOrToEndInvocation(invocation, infoCache, invocationSyntax, targetMethod);
}
private static Result? AnalyzeTwoArgumentStringRemoveInvocation(
IInvocationOperation invocation,
InfoCache infoCache,
InvocationExpressionSyntax invocationSyntax,
IMethodSymbol targetMethod,
MemberInfo memberInfo)
{
Contract.ThrowIfNull(invocation.Instance);
var startOperation = invocation.Arguments[0].Value;
var lengthOperation = invocation.Arguments[1].Value;
if (!IsValidIndexing(invocation, infoCache, targetMethod))
return null;
if (IsConstantInt32(startOperation, value: 0))
{
// `string.Remove(0, string.Length - x)` or `string.Remove(0, x)`
// Becomes `string[^x..]` or `string[x..]`
return new Result(
ResultKind.Computed,
invocation, invocationSyntax,
targetMethod, memberInfo,
op1: lengthOperation,
op2: null);
}
if (IsSubtraction(startOperation, out var subtraction))
{
// `string.Remove(string.Length - x, x)` becomes `string[..^x]`
if (!IsInstanceLengthCheck(memberInfo.LengthLikeProperty, invocation.Instance, subtraction.LeftOperand))
return null;
if (!CSharpSyntaxFacts.Instance.AreEquivalent(lengthOperation.Syntax, subtraction.RightOperand.Syntax))
return null;
return new Result(
ResultKind.Constant,
invocation, invocationSyntax,
targetMethod, memberInfo,
op1: lengthOperation,
op2: null);
}
else if (IsSubtraction(lengthOperation, out subtraction))
{
// `string.Remove(x, string.Length - x)` becomes `string[..x]`
if (!IsInstanceLengthCheck(memberInfo.LengthLikeProperty, invocation.Instance, subtraction.LeftOperand))
return null;
if (!CSharpSyntaxFacts.Instance.AreEquivalent(startOperation.Syntax, subtraction.RightOperand.Syntax))
return null;
return new Result(
ResultKind.Constant,
invocation, invocationSyntax,
targetMethod, memberInfo,
op1: startOperation,
op2: null);
}
return null;
}
private static Result? AnalyzeTwoArgumentSubtractionInvocation(
IInvocationOperation invocation,
InfoCache infoCache,
InvocationExpressionSyntax invocationSyntax,
IMethodSymbol targetMethod)
{
Contract.ThrowIfNull(invocation.Instance);
// Second arg needs to be a subtraction for: `end - e2`. Once we've seen that we have
// that, try to see if we're calling into some sort of Slice method with a matching
// indexer or overload
if (!IsSubtraction(invocation.Arguments[1].Value, out var subtraction) ||
!infoCache.TryGetMemberInfo(targetMethod, out var memberInfo))
{
return null;
}
if (!IsValidIndexing(invocation, infoCache, targetMethod))
return null;
// See if we have: (start, end - start). Specifically where the start operation it the
// same as the right side of the subtraction.
var startOperation = invocation.Arguments[0].Value;
if (CSharpSyntaxFacts.Instance.AreEquivalent(startOperation.Syntax, subtraction.RightOperand.Syntax))
{
return new Result(
ResultKind.Computed,
invocation, invocationSyntax,
targetMethod, memberInfo,
startOperation, subtraction.LeftOperand);
}
// See if we have: (constant1, s.Length - constant2). The constants don't have to be
// the same value. This will convert over to s[constant1..(constant - constant1)]
if (IsConstantInt32(startOperation) &&
IsConstantInt32(subtraction.RightOperand) &&
IsInstanceLengthCheck(memberInfo.LengthLikeProperty, invocation.Instance, subtraction.LeftOperand))
{
return new Result(
ResultKind.Constant,
invocation, invocationSyntax,
targetMethod, memberInfo,
startOperation, subtraction.RightOperand);
}
return null;
}
private static Result? AnalyzeTwoArgumentFromStartOrToEndInvocation(
IInvocationOperation invocation,
InfoCache infoCache,
InvocationExpressionSyntax invocationSyntax,
IMethodSymbol targetMethod)
{
Contract.ThrowIfNull(invocation.Instance);
// if we have `x.Substring(0, end)` then that can just become `x[..end]`
// if we have `x.Substring(0, x.Length)` then that can just become `x[..]`
// if we have `x.Substring(0, x.Length - n)` then that is handled in AnalyzeTwoArgumentSubtractionInvocation
var startOperation = invocation.Arguments[0].Value;
if (!IsConstantInt32(startOperation, value: 0) ||
!infoCache.TryGetMemberInfo(targetMethod, out var memberInfo))
{
return null;
}
if (!IsValidIndexing(invocation, infoCache, targetMethod))
return null;
return new Result(
ResultKind.Computed,
invocation,
invocationSyntax,
targetMethod,
memberInfo,
startOperation,
invocation.Arguments[1].Value);
}
private static bool IsValidIndexing(IInvocationOperation invocation, InfoCache infoCache, IMethodSymbol targetMethod)
{
var indexer = GetIndexer(targetMethod.ContainingType, infoCache.RangeType, targetMethod.ContainingType);
// Need to make sure that if the target method is being written to, that the indexer returns a ref, is a read/write property,
// or the syntax allows for the slice method to be run
return !invocation.Syntax.IsLeftSideOfAnyAssignExpression() || indexer == null || !IsWriteableIndexer(invocation, indexer);
}
private Diagnostic CreateDiagnostic(Result result, NotificationOption2 notificationOption, AnalyzerOptions analyzerOptions)
{
// Keep track of the invocation node
var invocation = result.Invocation;
// Mark the span under the two arguments to .Slice(..., ...) as what we will be
// updating.
var arguments = invocation.ArgumentList.Arguments;
var location = Location.Create(invocation.SyntaxTree,
TextSpan.FromBounds(arguments.First().SpanStart, arguments.Last().Span.End));
return DiagnosticHelper.Create(
Descriptor,
location,
notificationOption,
analyzerOptions,
[invocation.GetLocation()],
ImmutableDictionary<string, string?>.Empty,
result.SliceLikeMethod.Name);
}
private static bool IsConstantInt32(IOperation operation, int? value = null)
=> operation.ConstantValue is { HasValue: true, Value: int i } &&
(value == null || i == value);
private static bool IsWriteableIndexer(IInvocationOperation invocation, IPropertySymbol indexer)
{
var refReturnMismatch = indexer.ReturnsByRef != invocation.TargetMethod.ReturnsByRef;
var indexerIsReadWrite = indexer.IsWriteableFieldOrProperty();
return refReturnMismatch && !indexerIsReadWrite;
}
}
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