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Description of Problem: The spec allows Unicode escape sequences within identifiers, but only if the escaped character is a valid character within the identifier. mcs allows *any* character
Steps to reproduce the problem:
1. Compile this line of code within a method:
string x\u0020y = "";
Actual Results: It compiles, declaring a variable with identifier xy
Expected Results: Compile-time error.
How often does this happen? Always.
Validated against version 22.214.171.124 (not listed in the version list above!) and against head.
Piece of code in error:
(If the escaped character isn't a valid identifier, it should put it back and break out of the loop.)
Right. According to documentation: https://msdn.microsoft.com/en-us/library/aa664670.aspx in the identifier can be used any unicode character from following character classes: Lu, Ll, Lt, Lm, Lo, Nl, Mn, Mc, Nd, Pc, and Cf (except first letter, which should be one of the character from classes: Lu, Ll, Lt, Lm, Lo or underscore).
I'm working on pull request now.
I also noted, that there is also problem with first character in the identifier. It will be fixed in my patch too.
Now I see that Nl is also letter-character, but IsLetter doesn't treat this characters as letter-character, so it should be explicitly checked in is_identifier_start_character method.
My pull request which solves problem: https://github.com/mono/mono/pull/1601
Fixed in master