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[VS] FOREACH VAR: resolve the loop variable of generic collections and arrays #2129

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Merged
RobertvanderHulst merged 1 commit into from
Oct 27, 2026
+100 −4
Merged

[VS] FOREACH VAR: resolve the loop variable of generic collections and arrays #2129

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104 changes: 100 additions & 4 deletions src/VisualStudio/LanguageService/Lookup/XSharpLookup.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -99,7 +99,8 @@ static public IList<IXSymbol> FindIdentifier(XSharpSearchLocation location, stri
variable.ResolvedType = types.FirstOrDefault();
if (variable.ResolvedType != null && variable.ResolvedType.FullName != KnownTypes.SystemArray)
{
variable.TypeName = variable.ResolvedType.FullName;
// keep the type arguments of the declaration: List<Customer> must not become List<T>
variable.TypeName = WithTypeArguments(variable.ResolvedType.FullName, variable.TypeName);
}
}
}
Expand Down Expand Up @@ -137,7 +138,11 @@ static public IList<IXSymbol> FindIdentifier(XSharpSearchLocation location, stri
var type = ResolveImpliedType(location, xVar, currentType, visibility);
if (type != null)
{
xVar.TypeName = type.FullName.GetXSharpTypeName();
var typeName = type.FullName.GetXSharpTypeName();
// ResolveImpliedCollection stores the element type with its type arguments, e.g. KeyValuePair<STRING,Customer>
if (xVar.ImpliedKind == ImpliedKind.InCollection && type.IsGeneric)
typeName = WithTypeArguments(typeName, xVar.TypeName);
xVar.TypeName = typeName;
}
}
}
Expand Down Expand Up @@ -380,14 +385,99 @@ private static IXTypeSymbol ResolveImpliedCollection(XSharpSearchLocation locati
var elementType = GetTypeNameFromSymbol(location, element);
if (elementType.EndsWith("[]"))
{
return GetArrayType(location, elementType.Substring(0, elementType.Length - 2));
// the loop variable has the type of the array element, not the array type
return SearchType(location, elementType.Substring(0, elementType.Length - 2)).FirstOrDefault();
}
var type = GetTypeFromSymbol(location, element);
var enumType = GetEnumerableElementTypeName(type, elementType);
if (enumType != null)
{
var ftype = SearchType(location, enumType).FirstOrDefault();
if (ftype != null)
{
xVar.TypeName = enumType;
return ftype;
}
}
var etype = getElementType(type, location, element);

return etype;
}

private static string GetEnumerableElementTypeName(IXTypeSymbol type, string collectionTypeName)
{
// For a generic collection the loop variable has the type argument of IEnumerable<T>, with the
// type arguments of the collection filled in: Dictionary<STRING,Customer> -> KeyValuePair<STRING,Customer>
// The indexer is no good here: Dictionary<TKey,TValue>[TKey] returns TValue
if (type is XPETypeSymbol peType && peType.IsGeneric && peType.TypeDef != null)
{
var typeParams = peType.TypeParameters;
var typeArgs = GetTypeArguments(collectionTypeName);
if (typeArgs.Count != typeParams.Count)
return null;
const string enumerable = "System.Collections.Generic.IEnumerable`1";
if (peType.TypeDef.FullName == enumerable)
return typeArgs[0];
foreach (var impl in peType.TypeDef.Interfaces)
{
if (impl.InterfaceType is Mono.Cecil.GenericInstanceType git && git.ElementType.FullName == enumerable)
{
var name = git.GenericArguments[0].FullName.GetXSharpTypeName();
return System.Text.RegularExpressions.Regex.Replace(name, @"\w+", m =>
{
var index = typeParams.IndexOf(m.Value);
return index >= 0 ? typeArgs[index] : m.Value;
});
}
}
}
return null;
}

private static IList<string> GetTypeArguments(string typeName)
{
// List<Customer> -> Customer, Dictionary<STRING, List<INT>> -> STRING, List<INT>
var result = new List<string>();
var pos = typeName?.IndexOf('<') ?? -1;
if (pos <= 0 || !typeName.EndsWith(">"))
return result;
int level = 0;
int start = pos + 1;
for (int i = start; i < typeName.Length - 1; i++)
{
switch (typeName[i])
{
case '<':
level += 1;
break;
case '>':
level -= 1;
break;
case ',':
if (level == 0)
{
result.Add(typeName.Substring(start, i - start).Trim());
start = i + 1;
}
break;
}
}
result.Add(typeName.Substring(start, typeName.Length - 1 - start).Trim());
return result;
}

private static string WithTypeArguments(string resolvedName, string declaredName)
{
// System.Collections.Generic.List<T> + List<Customer> -> System.Collections.Generic.List<Customer>
var typeArgs = GetTypeArguments(declaredName);
if (typeArgs.Count == 0)
return resolvedName;
var pos = resolvedName.IndexOf('<');
if (pos > 0)
resolvedName = resolvedName.Substring(0, pos);
return resolvedName + "<" + string.Join(",", typeArgs) + ">";
}

private static IXTypeSymbol getElementType(IXTypeSymbol type, XSharpSearchLocation location, IXSymbol element)
{
string elementType;
Expand Down Expand Up @@ -1166,7 +1256,13 @@ enum PPUDCType : byte
if (xmember.ParentType != null && xmember.ParentType.IsGeneric && symbols.Count > 0)
{
result.Clear();
result.Add(AdjustGenericMember(xmember, symbols.Peek()));
var adjusted = AdjustGenericMember(xmember, symbols.Peek());
if (adjusted.TypeName != xmember.TypeName)
{
// the clone still has the type of the type parameter (TValue), completion needs the real type
adjusted.ResolvedType = SearchType(location, adjusted.TypeName).FirstOrDefault();
}
result.Add(adjusted);
}
else
{
Expand Down