Fix type parsing error returned for type names with invalid start of assembly name

src/libraries/Common/src/System/Reflection/TypeNameParser.cs

@@ -48,6 +48,8 @@ private TypeNameParser(ReadOnlySpan<char> name)
  return null;
 
  assemblyName = GetNextAssemblyName();
+ if (assemblyName is null)
+ return null;
  Debug.Assert(Peek == TokenType.End);
  }
 
@@ -126,7 +128,7 @@ private TypeNameParser(ReadOnlySpan<char> name)
  return null;
 
  // Because "[" is used both for generic arguments and array indexes, we must peek two characters deep.
- if (!(Peek == TokenType.OpenSqBracket && (PeekSecond == TokenType.Other || PeekSecond == TokenType.OpenSqBracket)))
+ if (!(Peek is TokenType.OpenSqBracket && (PeekSecond is TokenType.Other or TokenType.OpenSqBracket)))
  return namedType;
 
  Skip();
@@ -328,9 +330,10 @@ private TokenType GetNextToken()
  // Lex the next segment as the assembly name at the end of an assembly-qualified type name. (Do not use for
  // assembly names embedded inside generic type arguments.)
  //
- private string GetNextAssemblyName()
+ private string? GetNextAssemblyName()
  {
- SkipWhiteSpace();
+ if (!StartAssemblyName())
+ return null;
 
  string assemblyName = new string(_input.Slice(_index));
  _index = _input.Length;
@@ -344,7 +347,8 @@ private string GetNextAssemblyName()
  //
  private string? GetNextEmbeddedAssemblyName()
  {
- SkipWhiteSpace();
+ if (!StartAssemblyName())
+ return null;
 
  ValueStringBuilder sb = new ValueStringBuilder(stackalloc char[64]);
 
@@ -382,6 +386,18 @@ private string GetNextAssemblyName()
  return sb.ToString();
  }
 
+ private bool StartAssemblyName()
+ {
+ // Compat: Treat invalid starting token of assembly name as type name parsing error instead of assembly name parsing error. This only affects
+ // exception returned by the parser.
+ if (Peek is TokenType.End or TokenType.Comma)
+ {
+ ParseError();
+ return false;
+ }
+ return true;
+ }
+
  //
  // Classify a character as a TokenType. (Fortunately, all tokens in type name strings other than identifiers are single-character tokens.)
  //

src/libraries/System.Reflection/tests/GetTypeTests.cs

@@ -269,6 +269,16 @@ public void GetType_GenericTypeArgumentList()
  Assert.Equal(typeof(System.Reflection.Tests.GenericClass<System.String>), Type.GetType("System.Reflection.Tests.GenericClass`1[[System.String, System.Private.CoreLib]]", throwOnError: true));
  Assert.Throws<FileNotFoundException>(() => Type.GetType("System.Reflection.Tests.GenericClass`1[[Bogus, BogusAssembly]]", throwOnError: true));
  }
+
+ [Fact]
+ [ActiveIssue("https://github.com/dotnet/runtime/issues/37871", TestRuntimes.Mono)]
+ public void GetType_InvalidAssemblyName()
+ {
+ Assert.Null(Type.GetType("MissingAssemblyName, "));
+ Assert.Null(Type.GetType("ExtraComma, ,"));
+ Assert.Null(Type.GetType("ExtraComma, , System.Runtime"));
+ Assert.Throws<FileLoadException>(() => Type.GetType("System.Object, System.Runtime, Version=x.y"));
+ }
  }
 
  namespace MyNamespace1