File: Completion\Providers\ImportCompletionProvider\ExtensionMethodImportCompletionHelper.SymbolComputer.cs
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Project: src\src\Features\Core\Portable\Microsoft.CodeAnalysis.Features.csproj (Microsoft.CodeAnalysis.Features)
// 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.Concurrent;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.FindSymbols;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Microsoft.CodeAnalysis.Shared.Utilities;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Completion.Providers;
 
internal static partial class ExtensionMethodImportCompletionHelper
{
    private sealed class SymbolComputer
    {
        private readonly int _position;
        private readonly Document _originatingDocument;
 
        /// <summary>
        /// The semantic model provided for <see cref="_originatingDocument"/>. This may be a speculative semantic
        /// model with limited validity based on the context surrounding <see cref="_position"/>.
        /// </summary>
        private readonly SemanticModel _originatingSemanticModel;
        private readonly ITypeSymbol _receiverTypeSymbol;
        private readonly ImmutableArray<string> _receiverTypeNames;
        private readonly ISet<string> _namespaceInScope;
        private readonly IImportCompletionCacheService<ExtensionMethodImportCompletionCacheEntry, object> _cacheService;
 
        // This dictionary is used as cache among all projects and PE references. 
        // The key is the receiver type as in the extension method declaration (symbol retrived from originating compilation).
        // The value indicates if we can reduce an extension method with this receiver type given receiver type.
        private readonly ConcurrentDictionary<ITypeSymbol, bool> _checkedReceiverTypes = [];
 
        public SymbolComputer(
            Document document,
            SemanticModel semanticModel,
            ITypeSymbol receiverTypeSymbol,
            int position,
            ISet<string> namespaceInScope)
        {
            _originatingDocument = document;
            _originatingSemanticModel = semanticModel;
            _receiverTypeSymbol = receiverTypeSymbol;
            _position = position;
            _namespaceInScope = namespaceInScope;
 
            var receiverTypeNames = GetReceiverTypeNames(receiverTypeSymbol);
            _receiverTypeNames = AddComplexTypes(receiverTypeNames);
            _cacheService = GetCacheService(document.Project);
        }
 
        private static IImportCompletionCacheService<ExtensionMethodImportCompletionCacheEntry, object> GetCacheService(Project project)
            => project.Solution.Services.GetRequiredService<IImportCompletionCacheService<ExtensionMethodImportCompletionCacheEntry, object>>();
 
        private static string? GetPEReferenceCacheKey(PortableExecutableReference peReference)
            => peReference.FilePath ?? peReference.Display;
 
        /// <summary>
        /// Force create/update all relevant indices
        /// </summary>
        public static void QueueCacheWarmUpTask(Project project)
        {
            GetCacheService(project).WorkQueue.AddWork(project);
        }
 
        public static async ValueTask UpdateCacheAsync(Project project, CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();
            var cacheService = GetCacheService(project);
 
            foreach (var relevantProject in GetAllRelevantProjects(project))
                await GetUpToDateCacheEntryAsync(relevantProject, cacheService, cancellationToken).ConfigureAwait(false);
 
            foreach (var peReference in GetAllRelevantPeReferences(project))
                await SymbolTreeInfo.GetInfoForMetadataReferenceAsync(project.Solution, peReference, checksum: null, cancellationToken).ConfigureAwait(false);
        }
 
        public async Task<(ImmutableArray<IMethodSymbol> symbols, bool isPartialResult)> GetExtensionMethodSymbolsAsync(bool forceCacheCreation, bool hideAdvancedMembers, CancellationToken cancellationToken)
        {
            try
            {
                // Find applicable symbols in parallel
                var peReferenceMethodSymbolsTask = ProducerConsumer<IMethodSymbol?>.RunParallelAsync(
                    source: GetAllRelevantPeReferences(_originatingDocument.Project),
                    produceItems: static (peReference, callback, args, cancellationToken) =>
                        args.@this.GetExtensionMethodSymbolsFromPeReferenceAsync(peReference, callback, args.forceCacheCreation, cancellationToken),
                    args: (@this: this, forceCacheCreation),
                    cancellationToken);
 
                var projectMethodSymbolsTask = ProducerConsumer<IMethodSymbol?>.RunParallelAsync(
                    source: GetAllRelevantProjects(_originatingDocument.Project),
                    produceItems: static (project, callback, args, cancellationToken) =>
                        args.@this.GetExtensionMethodSymbolsFromProjectAsync(project, callback, args.forceCacheCreation, cancellationToken),
                    args: (@this: this, forceCacheCreation),
                    cancellationToken);
 
                var results = await Task.WhenAll(peReferenceMethodSymbolsTask, projectMethodSymbolsTask).ConfigureAwait(false);
 
                var isPartialResult = false;
 
                using var _ = ArrayBuilder<IMethodSymbol>.GetInstance(results[0].Length + results[1].Length, out var symbols);
                foreach (var methodArray in results)
                {
                    foreach (var method in methodArray)
                    {
                        // `null` indicates we don't have the index ready for the corresponding project/PE.
                        // returns what we have even it means we only show partial results.
                        if (method is null)
                        {
                            isPartialResult = true;
                        }
                        else
                        {
                            symbols.Add(method);
                        }
                    }
                }
 
                var browsableSymbols = symbols
                    .ToImmutable()
                    .FilterToVisibleAndBrowsableSymbols(hideAdvancedMembers, _originatingSemanticModel.Compilation);
 
                return (browsableSymbols, isPartialResult);
            }
            finally
            {
                // If we are not force creating/updating the cache, an update task needs to be queued in background.
                if (!forceCacheCreation)
                    GetCacheService(_originatingDocument.Project).WorkQueue.AddWork(_originatingDocument.Project);
            }
        }
 
        // Returns all referenced projects and originating project itself.
        private static ImmutableArray<Project> GetAllRelevantProjects(Project project)
        {
            var graph = project.Solution.GetProjectDependencyGraph();
            var relevantProjectIds = graph.GetProjectsThatThisProjectTransitivelyDependsOn(project.Id).Concat(project.Id);
            return relevantProjectIds.Select(project.Solution.GetRequiredProject).Where(p => p.SupportsCompilation).ToImmutableArray();
        }
 
        // Returns all PEs referenced by originating project.
        private static ImmutableArray<PortableExecutableReference> GetAllRelevantPeReferences(Project project)
            => project.MetadataReferences.OfType<PortableExecutableReference>().ToImmutableArray();
 
        private async Task GetExtensionMethodSymbolsFromProjectAsync(
            Project project,
            Action<IMethodSymbol?> callback,
            bool forceCacheCreation,
            CancellationToken cancellationToken)
        {
            ExtensionMethodImportCompletionCacheEntry cacheEntry;
            if (forceCacheCreation)
            {
                cacheEntry = await GetUpToDateCacheEntryAsync(project, _cacheService, cancellationToken).ConfigureAwait(false);
            }
            else if (!_cacheService.ProjectItemsCache.TryGetValue(project.Id, out cacheEntry))
            {
                // Use cached data if available, even checksum doesn't match. otherwise, returns null indicating cache not ready.
                callback(null);
                return;
            }
 
            if (!cacheEntry.ContainsExtensionMethod)
                return;
 
            var originatingAssembly = _originatingSemanticModel.Compilation.Assembly;
            var filter = CreateAggregatedFilter(cacheEntry);
 
            // Avoid recalculating a compilation for the originating document, particularly for the case where the
            // provided semantic model is a speculative semantic model.
            var compilation = project == _originatingDocument.Project
                ? _originatingSemanticModel.Compilation
                : await project.GetRequiredCompilationAsync(cancellationToken).ConfigureAwait(false);
            var assembly = compilation.Assembly;
            var internalsVisible = originatingAssembly.IsSameAssemblyOrHasFriendAccessTo(assembly);
 
            var matchingMethodSymbols = GetPotentialMatchingSymbolsFromAssembly(
                compilation.Assembly, filter, internalsVisible, cancellationToken);
 
            if (project == _originatingDocument.Project)
            {
                GetExtensionMethodsForSymbolsFromSameCompilation(matchingMethodSymbols, callback, cancellationToken);
            }
            else
            {
                GetExtensionMethodsForSymbolsFromDifferentCompilation(matchingMethodSymbols, callback, cancellationToken);
            }
        }
 
        private async Task GetExtensionMethodSymbolsFromPeReferenceAsync(
            PortableExecutableReference peReference,
            Action<IMethodSymbol?> callback,
            bool forceCacheCreation,
            CancellationToken cancellationToken)
        {
            SymbolTreeInfo? symbolInfo;
            if (forceCacheCreation)
            {
                symbolInfo = await SymbolTreeInfo.GetInfoForMetadataReferenceAsync(
                    _originatingDocument.Project.Solution, peReference, checksum: null, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                var cachedInfoTask = SymbolTreeInfo.TryGetCachedInfoForMetadataReferenceIgnoreChecksumAsync(peReference, cancellationToken);
                if (cachedInfoTask.IsCompleted)
                {
                    // Use cached data if available, even checksum doesn't match. We will update the cache in the background.
                    symbolInfo = await cachedInfoTask.ConfigureAwait(false);
                }
                else
                {
                    // No cached data immediately available, returns null to indicate index not ready
                    callback(null);
                    return;
                }
            }
 
            if (symbolInfo is null ||
                !symbolInfo.ContainsExtensionMethod ||
                _originatingSemanticModel.Compilation.GetAssemblyOrModuleSymbol(peReference) is not IAssemblySymbol assembly)
            {
                return;
            }
 
            var filter = CreateAggregatedFilter(symbolInfo);
            var internalsVisible = _originatingSemanticModel.Compilation.Assembly.IsSameAssemblyOrHasFriendAccessTo(assembly);
 
            var matchingMethodSymbols = GetPotentialMatchingSymbolsFromAssembly(assembly, filter, internalsVisible, cancellationToken);
 
            GetExtensionMethodsForSymbolsFromSameCompilation(matchingMethodSymbols, callback, cancellationToken);
        }
 
        private void GetExtensionMethodsForSymbolsFromDifferentCompilation(
            MultiDictionary<ITypeSymbol, IMethodSymbol> matchingMethodSymbols,
            Action<IMethodSymbol?> callback,
            CancellationToken cancellationToken)
        {
            // Matching extension method symbols are grouped based on their receiver type.
            foreach (var (declaredReceiverType, methodSymbols) in matchingMethodSymbols)
            {
                cancellationToken.ThrowIfCancellationRequested();
 
                var declaredReceiverTypeInOriginatingCompilation = SymbolFinder.FindSimilarSymbols(declaredReceiverType, _originatingSemanticModel.Compilation, cancellationToken).FirstOrDefault();
                if (declaredReceiverTypeInOriginatingCompilation == null)
                {
                    // Bug: https://github.com/dotnet/roslyn/issues/45404
                    // SymbolFinder.FindSimilarSymbols would fail if originating and referenced compilation targeting different frameworks say net472 and netstandard respectively.
                    // Here's SymbolKey for System.String from those two framework as an example:
                    //
                    //  {1 (D "String" (N "System" 0 (N "" 0 (U (S "netstandard" 4) 3) 2) 1) 0 0 (% 0) 0)}
                    //  {1 (D "String" (N "System" 0 (N "" 0 (U (S "mscorlib" 4) 3) 2) 1) 0 0 (% 0) 0)}
                    //
                    // Also we don't use the "ignoreAssemblyKey" option for SymbolKey resolution because its perfermance doesn't meet our requirement.
                    continue;
                }
 
                if (_checkedReceiverTypes.TryGetValue(declaredReceiverTypeInOriginatingCompilation, out var cachedResult) && !cachedResult)
                {
                    // If we already checked an extension method with same receiver type before, and we know it can't be applied
                    // to the receiverTypeSymbol, then no need to proceed methods from this group..
                    continue;
                }
 
                // This is also affected by the symbol resolving issue mentioned above, which means in case referenced projects
                // are targeting different framework, we will miss extension methods with any framework type in their signature from those projects.
                var isFirstMethod = true;
                foreach (var methodInOriginatingCompilation in methodSymbols.Select(s => SymbolFinder.FindSimilarSymbols(s, _originatingSemanticModel.Compilation).FirstOrDefault()).WhereNotNull())
                {
                    if (isFirstMethod)
                    {
                        isFirstMethod = false;
 
                        // We haven't seen this receiver type yet. Try to check by reducing one extension method
                        // to the given receiver type and save the result.
                        if (!cachedResult)
                        {
                            // If this is the first symbol we retrived from originating compilation,
                            // try to check if we can apply it to given receiver type, and save result to our cache.
                            // Since method symbols are grouped by their declared receiver type, they are either all matches to the receiver type
                            // or all mismatches. So we only need to call ReduceExtensionMethod on one of them.
                            var reducedMethodSymbol = methodInOriginatingCompilation.ReduceExtensionMethod(_receiverTypeSymbol);
                            cachedResult = reducedMethodSymbol != null;
                            _checkedReceiverTypes[declaredReceiverTypeInOriginatingCompilation] = cachedResult;
 
                            // Now, cachedResult being false means method doesn't match the receiver type,
                            // stop processing methods from this group.
                            if (!cachedResult)
                            {
                                break;
                            }
                        }
                    }
 
                    if (_originatingSemanticModel.IsAccessible(_position, methodInOriginatingCompilation))
                        callback(methodInOriginatingCompilation);
                }
            }
        }
 
        private void GetExtensionMethodsForSymbolsFromSameCompilation(
            MultiDictionary<ITypeSymbol, IMethodSymbol> matchingMethodSymbols,
            Action<IMethodSymbol?> callback,
            CancellationToken cancellationToken)
        {
            // Matching extension method symbols are grouped based on their receiver type.
            foreach (var (receiverType, methodSymbols) in matchingMethodSymbols)
            {
                cancellationToken.ThrowIfCancellationRequested();
 
                // If we already checked an extension method with same receiver type before, and we know it can't be applied
                // to the receiverTypeSymbol, then no need to proceed further.
                if (_checkedReceiverTypes.TryGetValue(receiverType, out var cachedResult) && !cachedResult)
                    continue;
 
                // We haven't seen this type yet. Try to check by reducing one extension method
                // to the given receiver type and save the result.
                if (!cachedResult)
                {
                    var reducedMethodSymbol = methodSymbols.First().ReduceExtensionMethod(_receiverTypeSymbol);
                    cachedResult = reducedMethodSymbol != null;
                    _checkedReceiverTypes[receiverType] = cachedResult;
                }
 
                // Receiver type matches the receiver type of the extension method declaration.
                // We can add accessible ones to the item builder.
                if (cachedResult)
                {
                    foreach (var methodSymbol in methodSymbols)
                    {
                        if (_originatingSemanticModel.IsAccessible(_position, methodSymbol))
                            callback(methodSymbol);
                    }
                }
            }
        }
 
        private MultiDictionary<ITypeSymbol, IMethodSymbol> GetPotentialMatchingSymbolsFromAssembly(
            IAssemblySymbol assembly,
            MultiDictionary<string, (string methodName, string receiverTypeName)> extensionMethodFilter,
            bool internalsVisible,
            CancellationToken cancellationToken)
        {
            var builder = new MultiDictionary<ITypeSymbol, IMethodSymbol>();
 
            // The filter contains all the extension methods that potentially match the receiver type.
            // We use it as a guide to selectively retrive container and member symbols from the assembly.
            foreach (var (fullyQualifiedContainerName, methodInfo) in extensionMethodFilter)
            {
                // First try to filter out types from already imported namespaces
                var indexOfLastDot = fullyQualifiedContainerName.LastIndexOf('.');
                var qualifiedNamespaceName = indexOfLastDot > 0 ? fullyQualifiedContainerName[..indexOfLastDot] : string.Empty;
 
                if (_namespaceInScope.Contains(qualifiedNamespaceName))
                {
                    continue;
                }
 
                // Container of extension method (static class in C# and Module in VB) can't be generic or nested.
                var containerSymbol = assembly.GetTypeByMetadataName(fullyQualifiedContainerName);
 
                if (containerSymbol == null
                    || !containerSymbol.MightContainExtensionMethods
                    || !IsAccessible(containerSymbol, internalsVisible))
                {
                    continue;
                }
 
                // Now we have the container symbol, first try to get member extension method symbols that matches our syntactic filter,
                // then further check if those symbols matches semantically.
                foreach (var (methodName, receiverTypeName) in methodInfo)
                {
                    cancellationToken.ThrowIfCancellationRequested();
 
                    var methodSymbols = containerSymbol.GetMembers(methodName).OfType<IMethodSymbol>();
 
                    foreach (var methodSymbol in methodSymbols)
                    {
                        if (MatchExtensionMethod(methodSymbol, receiverTypeName, internalsVisible, out var receiverType))
                        {
                            // Find a potential match.
                            builder.Add(receiverType!, methodSymbol);
                        }
                    }
                }
            }
 
            return builder;
 
            static bool MatchExtensionMethod(IMethodSymbol method, string filterReceiverTypeName, bool internalsVisible, out ITypeSymbol? receiverType)
            {
                receiverType = null;
                if (!method.IsExtensionMethod || method.Parameters.IsEmpty || !IsAccessible(method, internalsVisible))
                {
                    return false;
                }
 
                // We get a match if the receiver type name match. 
                // For complex type, we would check if it matches with filter on whether it's an array.
                if (filterReceiverTypeName.Length > 0 && !string.Equals(filterReceiverTypeName, GetReceiverTypeName(method.Parameters[0].Type), StringComparison.Ordinal))
                {
                    return false;
                }
 
                receiverType = method.Parameters[0].Type;
                return true;
            }
 
            // An quick accessibility check based on declared accessibility only, a semantic based check is still required later.
            // Since we are dealing with extension methods and their container (top level static class and modules), only public,
            // internal and private modifiers are in play here. 
            // Also, this check is called for a method symbol only when the container was checked and is accessible.
            static bool IsAccessible(ISymbol symbol, bool internalsVisible)
                => symbol.DeclaredAccessibility == Accessibility.Public ||
                (symbol.DeclaredAccessibility == Accessibility.Internal && internalsVisible);
        }
 
        /// <summary>
        /// Create a filter for extension methods from source.
        /// The filter is a map from fully qualified type name to info of extension methods it contains.
        /// </summary>
        private MultiDictionary<string, (string methodName, string receiverTypeName)> CreateAggregatedFilter(ExtensionMethodImportCompletionCacheEntry syntaxIndex)
        {
            var results = new MultiDictionary<string, (string, string)>();
 
            foreach (var receiverTypeName in _receiverTypeNames)
            {
                var methodInfos = syntaxIndex.ReceiverTypeNameToExtensionMethodMap[receiverTypeName];
                if (methodInfos.Count == 0)
                {
                    continue;
                }
 
                foreach (var methodInfo in methodInfos)
                {
                    results.Add(methodInfo.FullyQualifiedContainerName, (methodInfo.Name, receiverTypeName));
                }
            }
 
            return results;
        }
 
        /// <summary>
        /// Create filter for extension methods from metadata
        /// The filter is a map from fully qualified type name to info of extension methods it contains.
        /// </summary>
        private MultiDictionary<string, (string methodName, string receiverTypeName)> CreateAggregatedFilter(SymbolTreeInfo symbolInfo)
        {
            var results = new MultiDictionary<string, (string, string)>();
 
            foreach (var receiverTypeName in _receiverTypeNames)
            {
                var methodInfos = symbolInfo.GetExtensionMethodInfoForReceiverType(receiverTypeName);
                if (methodInfos.Count == 0)
                {
                    continue;
                }
 
                foreach (var methodInfo in methodInfos)
                {
                    results.Add(methodInfo.FullyQualifiedContainerName, (methodInfo.Name, receiverTypeName));
                }
            }
 
            return results;
        }
 
        /// <summary>
        /// Get the metadata name of all the base types and interfaces this type derived from.
        /// </summary>
        private static ImmutableArray<string> GetReceiverTypeNames(ITypeSymbol receiverTypeSymbol)
        {
            using var _ = PooledHashSet<string>.GetInstance(out var allTypeNamesBuilder);
            AddNamesForTypeWorker(receiverTypeSymbol, allTypeNamesBuilder);
            return [.. allTypeNamesBuilder];
 
            static void AddNamesForTypeWorker(ITypeSymbol receiverTypeSymbol, PooledHashSet<string> builder)
            {
                if (receiverTypeSymbol is ITypeParameterSymbol typeParameter)
                {
                    foreach (var constraintType in typeParameter.ConstraintTypes)
                    {
                        AddNamesForTypeWorker(constraintType, builder);
                    }
                }
                else
                {
                    builder.Add(GetReceiverTypeName(receiverTypeSymbol));
                    builder.AddRange(receiverTypeSymbol.GetBaseTypes().Select(t => t.MetadataName));
                    builder.AddRange(receiverTypeSymbol.GetAllInterfacesIncludingThis().Select(t => t.MetadataName));
 
                    // interface doesn't inherit from object, but is implicitly convertible to object type.
                    if (receiverTypeSymbol.IsInterfaceType())
                    {
                        builder.Add(nameof(Object));
                    }
                }
            }
        }
 
        /// <summary>
        /// Add strings represent complex types (i.e. "" for non-array types and "[]" for array types) to the receiver type, 
        /// so we would include in the filter info about extension methods with complex receiver type.
        /// </summary>
        private static ImmutableArray<string> AddComplexTypes(ImmutableArray<string> receiverTypeNames)
        {
            return
            [
                .. receiverTypeNames,
                FindSymbols.Extensions.ComplexReceiverTypeName,
                FindSymbols.Extensions.ComplexArrayReceiverTypeName,
            ];
        }
 
        private static string GetReceiverTypeName(ITypeSymbol typeSymbol)
        {
            switch (typeSymbol)
            {
                case INamedTypeSymbol namedType:
                    return namedType.MetadataName;
 
                case IArrayTypeSymbol arrayType:
                    var elementType = arrayType.ElementType;
                    while (elementType is IArrayTypeSymbol symbol)
                    {
                        elementType = symbol.ElementType;
                    }
 
                    var elementTypeName = GetReceiverTypeName(elementType);
 
                    // We do not differentiate array of different kinds sicne they are all represented in the indices as "NonArrayElementTypeName[]"
                    // e.g. int[], int[][], int[,], etc. are all represented as "int[]", whereas array of complex type such as T[] is "[]".
                    return elementTypeName + FindSymbols.Extensions.ArrayReceiverTypeNameSuffix;
 
                default:
                    // Complex types are represented by "";
                    return FindSymbols.Extensions.ComplexReceiverTypeName;
            }
        }
    }
}