What regular expression variant is used in Visual Studio code?

Question

I know that I can use Ruby's regular expressions in a tmLanguage file, however that seems not to be the case in other configuration files, e.g. for extensions. Take for example the firstLine value in the language contribution. I get errors when I use character classes (e.g. \s or \p{L}). Hence I wonder what is actually allowed there. How would you match whitespaces there?

Update: After the comments I tried this:

"firstLine": "^(lexer|parser)?\\s*grammar\\w+;"

which is supposed to match a first line like lexer grammar G1; or just grammar G1;. Is there a way to test if that RE works, because I have no validation otherwise?

Update 2:

It's essential to use the correct grammar and it will magically work:

"firstLine": "^(lexer|parser)?\\s*grammar\\s*\\w+\\s*;"

You didn't show a full `firstLine` value of your own, so I can't see if you remembered to escape the backslash, like `\\s`. — Andrew Morton, Aug 21 '16 at 15:07
No, I did not escape `\s`. It wasn't needed in my tmLanguage file. — Mike Lischke, Aug 21 '16 at 15:34
In your update, is the ending semicolon meant to be optional? You seem to have it as being required. As the file is json, you have to [escape the backslash](http://json.org/). — Andrew Morton, Aug 21 '16 at 15:46
As for testing, I suppose you could test it on files which you expect it to work with. — Andrew Morton, Aug 21 '16 at 15:47

score 1 · Accepted Answer · answered Aug 21 '16 at 15:24

1

.NET regular expressions use a syntax that is largely based on Perl 5, however it does add a few new features such as named capture groups and right to left matching, so the two should not be thought of as identical. Here is the full MSDN documentation for .NET regular expressions:

.NET Framework Regular Expressions

\s is a valid character class in .NET, but it is difficult to say exactly what the problem is without seeing the code you are trying. Andrew could be right, that you just did not escape the \.

answered Aug 21 '16 at 15:24

John Smith

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VS Code does not use .NET Regular Expressions. See also [this](https://stackoverflow.com/questions/42179046/what-flavor-of-regex-does-visual-studio-code-use) question. – Eric Feb 11 '17 at 18:39
@Eric, the question you refer to is about the search widget, not the syntax highlighting definition file used to create a new language... – Igor Popov May 22 '17 at 14:03
Yes, well the questions are practically identical. Not the content but the actual question header. – Eric May 25 '17 at 10:42

What regular expression variant is used in Visual Studio code?

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