Avoid variable length lookbehind

[am11]

• GH Linguist supports PCRE grammar, which supports variable (as well as fixed) length lookbehind.
• VSCode supports Oniguruma grammar, which only support fixed length lookbehind.

so the solution to keep both worlds happy is to use most common syntax; fixed length lookbehind.

[am11]

cc @Gerrit0, this should fix VSCode issue.

[Gerrit0]

This doesn't seem to do the right thing:

Screenshot

I'm not sure about Linguist, but TextMate regexes are not permitted to match across lines (microsoft/vscode-textmate#32), which makes properly handling the last two cases essentially impossible.

Am I missing some reason that we need lookbehind here at all? The following (with \s*$ branch to avoid detecting a conditional at EOL, for the last two cases) seems to do the trick

\\?(?!\\s*[?.\\[]|\\s*$)

Screenshot

[am11]

Updated. seems to work on linguist side as well. Thanks!

[am11]

lightshow with 5426265

[Gerrit0]

Shoot, I figured out why the lookbehind was there...

public class A {
    public void Nullish() {
        char s = ss ?? 'x'
        if (true) {} // if is wrong color
    }
}

This feels like something else is out of order though. Why is the grammar even getting to conditional expressions if null coalescing matches? This is my first foray into this bit of work, so I'm probably not understanding something else...

[am11]

That case is handled otherwise

csharp-tmLanguage/test/expressions.tests.ts

Line 3028 in 11731b4

describe("Null-coalescing Operator", () => {

would have failed in the CI.

[am11]

public class A {
    public void Nullish() {
-        char s = ss ?? 'x'
+        char s = ss ?? 'x';
        if (true) {} // if is wrong color
    }
}

[Gerrit0]

Oh! That makes sense, thanks!... too much time in TypeScript where I never have to type them and they will get automatically added on save.

[am11]

Regarding github/linguist repo, since now it supports (more superior) tree-sitter grammar (github-linguist/linguist#5483 (comment)), we maybe able to switch to https://github.com/tree-sitter/tree-sitter-c-sharp.

The code navigation feature in GitHub has already started to use it: https://docs.github.com/en/github/managing-files-in-a-repository/managing-files-on-github/navigating-code-on-github.

[JoeRobich]

@am11 Thanks!