Pattern Using (#27729)

src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs

@@ -3101,5 +3101,201 @@ internal virtual ImmutableArray<LabelSymbol> Labels
                 return ImmutableArray<LabelSymbol>.Empty;
             }
         }
+
+        /// <summary>
+        /// Perform a lookup for the specified method on the specified type.  Perform overload resolution
+        /// on the lookup results.
+        /// </summary>
+        /// <param name="patternType">Type to search.</param>
+        /// <param name="methodName">Method to search for.</param>
+        /// <param name="lookupResult">Passed in for reusability.</param>
+        /// <param name="warningsOnly">True if failures should result in warnings; false if they should result in errors.</param>
+        /// <param name="diagnostics">Populated with binding diagnostics.</param>
+        /// <returns>The desired method or null.</returns>
+        internal MethodSymbol FindPatternMethod(TypeSymbol patternType, string methodName, LookupResult lookupResult,
+                                                SyntaxNode syntaxExpr, bool warningsOnly, DiagnosticBag diagnostics,
+                                                SyntaxTree syntaxTree, MessageID messageID)
+        {
+            Debug.Assert(lookupResult.IsClear);
+
+            // Not using LookupOptions.MustBeInvocableMember because we don't want the corresponding lookup error.
+            // We filter out non-methods below.
+            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            this.LookupMembersInType(
+                lookupResult,
+                patternType,
+                methodName,
+                arity: 0,
+                basesBeingResolved: null,
+                options: LookupOptions.Default,
+                originalBinder: this,
+                diagnose: false,
+                useSiteDiagnostics: ref useSiteDiagnostics);
+
+            diagnostics.Add(syntaxExpr, useSiteDiagnostics);
+
+            if (!lookupResult.IsMultiViable)
+            {
+                ReportPatternMemberLookupDiagnostics(lookupResult, patternType, methodName, syntaxExpr, warningsOnly, diagnostics, messageID);
+                return null;
+            }
+
+            ArrayBuilder<MethodSymbol> candidateMethods = ArrayBuilder<MethodSymbol>.GetInstance();
+
+            foreach (Symbol member in lookupResult.Symbols)
+            {
+                if (member.Kind != SymbolKind.Method)
+                {
+                    candidateMethods.Free();
+
+                    if (warningsOnly)
+                    {
+                        ReportPatternWarning(diagnostics, patternType, member, syntaxExpr, messageID);
+                    }
+
+                    return null;
+                }
+
+                MethodSymbol method = (MethodSymbol)member;
+
+                // SPEC VIOLATION: The spec says we should apply overload resolution, but Dev10 uses
+                // some custom logic in ExpressionBinder.BindGrpToParams.  The biggest difference
+                // we've found (so far) is that it only considers methods with zero parameters
+                // (i.e. doesn't work with "params" or optional parameters).
+                if (!method.Parameters.Any())
+                {
+                    candidateMethods.Add((MethodSymbol)member);
+                }
+            }
+
+            MethodSymbol patternMethod = PerformPatternOverloadResolution(patternType, candidateMethods, syntaxExpr, warningsOnly, diagnostics, syntaxTree, messageID);
+
+            candidateMethods.Free();
+
+            return patternMethod;
+        }
+
+        /// <summary>
+        /// The overload resolution portion of FindPatternMethod.
+        /// </summary>
+        private MethodSymbol PerformPatternOverloadResolution(
+            TypeSymbol patternType, ArrayBuilder<MethodSymbol> candidateMethods,
+            SyntaxNode syntaxExpression, bool warningsOnly, DiagnosticBag diagnostics,
+            SyntaxTree syntaxTree, MessageID messageID)
+        {
+            ArrayBuilder<TypeSymbol> typeArguments = ArrayBuilder<TypeSymbol>.GetInstance();
+            AnalyzedArguments arguments = AnalyzedArguments.GetInstance();
+            OverloadResolutionResult<MethodSymbol> overloadResolutionResult = OverloadResolutionResult<MethodSymbol>.GetInstance();
+
+            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            // We create a dummy receiver of the invocation so MethodInvocationOverloadResolution knows it was invoked from an instance, not a type
+            var dummyReceiver = new BoundImplicitReceiver(syntaxExpression, patternType);
+            this.OverloadResolution.MethodInvocationOverloadResolution(
+                methods: candidateMethods,
+                typeArguments: typeArguments,
+                receiver: dummyReceiver,
+                arguments: arguments,
+                result: overloadResolutionResult,
+                useSiteDiagnostics: ref useSiteDiagnostics);
+            diagnostics.Add(syntaxExpression, useSiteDiagnostics);
+
+            MethodSymbol result = null;
+
+            if (overloadResolutionResult.Succeeded)
+            {
+                result = overloadResolutionResult.ValidResult.Member;
+
+                if (result.IsStatic || result.DeclaredAccessibility != Accessibility.Public)
+                {
+                    if (warningsOnly)
+                    {
+                        diagnostics.Add(ErrorCode.WRN_PatternStaticOrInaccessible, syntaxExpression.Location, patternType, messageID.Localize(), result);
+                    }
+
+                    result = null;
+                }
+                else if (result.CallsAreOmitted(syntaxTree))
+                {
+                    // Calls to this method are omitted in the current syntax tree, i.e it is either a partial method with no implementation part OR a conditional method whose condition is not true in this source file.
+                    // We don't want to allow this case, see StatementBinder::bindPatternToMethod.
+                    result = null;
+                }
+            }
+            else if (overloadResolutionResult.Results.Length > 1)
+            {
+                if (warningsOnly)
+                {
+                    diagnostics.Add(ErrorCode.WRN_PatternIsAmbiguous, syntaxExpression.Location, patternType, messageID.Localize(),
+                        overloadResolutionResult.Results[0].Member, overloadResolutionResult.Results[1].Member);
+                }
+            }
+
+            overloadResolutionResult.Free();
+            arguments.Free();
+            typeArguments.Free();
+
+            return result;
+        }
+
+        private void ReportPatternWarning(DiagnosticBag diagnostics, TypeSymbol patternType, Symbol patternMemberCandidate, SyntaxNode expression, MessageID messageID)
+        {
+            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            if (this.IsAccessible(patternMemberCandidate, ref useSiteDiagnostics))
+            {
+                diagnostics.Add(ErrorCode.WRN_PatternBadSignature, expression.Location, patternType, messageID.Localize(), patternMemberCandidate);
+            }
+
+            diagnostics.Add(expression, useSiteDiagnostics);
+        }
+
+        /// <summary>
+        /// Report appropriate diagnostics when lookup of a pattern member (i.e. GetEnumerator, Current, or MoveNext) fails.
+        /// </summary>
+        /// <param name="lookupResult">Failed lookup result.</param>
+        /// <param name="patternType">Type in which member was looked up.</param>
+        /// <param name="memberName">Name of looked up member.</param>
+        /// <param name="warningsOnly">True if failures should result in warnings; false if they should result in errors.</param>
+        /// <param name="diagnostics">Populated appropriately.</param>
+        internal void ReportPatternMemberLookupDiagnostics(
+            LookupResult lookupResult, TypeSymbol patternType,
+            string memberName, SyntaxNode expression,
+            bool warningsOnly, DiagnosticBag diagnostics,
+            MessageID messageID)
+        { 
+            if (lookupResult.Symbols.Any())
+            {
+                if (warningsOnly)
+                {
+                    ReportPatternWarning(diagnostics, patternType, lookupResult.Symbols.First(), expression, messageID);
+                }
+                else
+                {
+                    lookupResult.Clear();
+
+                    HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+                    this.LookupMembersInType(
+                        lookupResult,
+                        patternType,
+                        memberName,
+                        arity: 0,
+                        basesBeingResolved: null,
+                        options: LookupOptions.Default,
+                        originalBinder: this,
+                        diagnose: true,
+                        useSiteDiagnostics: ref useSiteDiagnostics);
+
+                    diagnostics.Add(expression, useSiteDiagnostics);
+
+                    if (lookupResult.Error != null)
+                    {
+                        diagnostics.Add(lookupResult.Error, expression.Location);
+                    }
+                }
+            }
+            else if (!warningsOnly)
+            {
+                diagnostics.Add(ErrorCode.ERR_NoSuchMember, expression.Location, patternType, memberName);
+            }
+        }
     }
 }