Update documentation/naming for retrieving collidable symbols.

src/Workspaces/CSharp/Portable/LanguageServices/CSharpSemanticFactsService.cs

@@ -26,7 +26,7 @@ private CSharpSemanticFactsService()
         {
         }
 
-        protected override IEnumerable<ISymbol> GetUsedSymbols(SemanticModel semanticModel, SyntaxNode location, SyntaxNode container, CancellationToken cancellationToken)
+        protected override IEnumerable<ISymbol> GetCollidableSymbols(SemanticModel semanticModel, SyntaxNode location, SyntaxNode container, CancellationToken cancellationToken)
         {
             // Get all the symbols visible to the current location.
             var visibleSymbols = semanticModel.LookupSymbols(location.SpanStart);
@@ -36,7 +36,7 @@ protected override IEnumerable<ISymbol> GetUsedSymbols(SemanticModel semanticMod
             // Walk through the enclosing block to find them, but avoid exploring local functions because
             //     a) Visible local function symbols would be returned from LookupSymbols
             //        (e.g. location is inside a local function or the local function method name).
-            //     b) Local function symbols are not affected by outer variables and do not contribute to the outer scope.
+            //     b) Symbols declared inside a local function do not cause collisions with symbols declared outside the local function, so avoid considering them.
             var symbolsInBlock = semanticModel.GetExistingSymbols(container, cancellationToken,
                 descendInto: n => !n.IsKind(SyntaxKind.LocalFunctionStatement));
 

src/Workspaces/Core/Portable/LanguageServices/SemanticsFactsService/AbstractSemanticFactsService.cs

@@ -60,13 +60,18 @@ internal abstract class AbstractSemanticFactsService
             var container = containerOpt ?? location.AncestorsAndSelf().FirstOrDefault(
                 a => syntaxFacts.IsExecutableBlock(a) || syntaxFacts.IsMethodBody(a));
 
-            var candidates = GetUsedSymbols(semanticModel, location, container, cancellationToken);
+            var candidates = GetCollidableSymbols(semanticModel, location, container, cancellationToken);
             var filteredCandidates = filter != null ? candidates.Where(filter) : candidates;
 
             return GenerateUniqueName(baseName, filteredCandidates.Select(s => s.Name).Concat(usedNames));
         }
 
-        protected virtual IEnumerable<ISymbol> GetUsedSymbols(SemanticModel semanticModel, SyntaxNode location, SyntaxNode container, CancellationToken cancellationToken)
+        /// <summary>
+        /// Retrieves all symbols that could collide with a symbol at the specified location.
+        /// A symbol can possibly collide with the location if it is available to that location and/or
+        /// could cause a compiler error if its name is re-used at that location.
+        /// </summary>
+        protected virtual IEnumerable<ISymbol> GetCollidableSymbols(SemanticModel semanticModel, SyntaxNode location, SyntaxNode container, CancellationToken cancellationToken)
             => semanticModel.LookupSymbols(location.SpanStart).Concat(semanticModel.GetExistingSymbols(container, cancellationToken));
 
         private SyntaxToken GenerateUniqueName(string baseName, IEnumerable<string> usedNames)