Problems reported:

parser/patterns/patternVariableDeclaration_topLevel:1:5: A pattern variable declaration may not appear outside a function or method.
var (a, b) = (0, 1);
    ^^^^^^

beginCompilationUnit(var)
  beginMetadataStar(var)
  endMetadataStar(0)
  beginTopLevelMember(var)
    handleRecoverableError(PatternVariableDeclarationOutsideFunctionOrMethod, (, ))
    beginFields(DeclarationKind.TopLevel, null, null, null, null, null, null, var, )
      handleNoType(var)
      handleIdentifier(, topLevelVariableDeclaration)
      beginFieldInitializer(=)
        beginParenthesizedExpressionOrRecordLiteral(()
          handleLiteralInt(0)
          handleLiteralInt(1)
        endRecordLiteral((, 2, null)
      endFieldInitializer(=, ))
    endTopLevelFields(null, null, null, null, null, var, 1, var, ;)
  endTopLevelDeclaration(;)
endCompilationUnit(1, )