newlines in `impl` definition break syntax highlighting

[fpdotmonkey]

Sublime Text Version

Build 4126

Rust Enhanced Version

v2.25.0

Operating system

OS Name Microsoft Windows 10 Home
Version 21H2 build 19044.1826

Expected behavior

For the following snippet, the trait name should be colored like normal text and the for keyword should colored like a keyword

impl ThisTraitHasAVeryLongNameWhichCausesTheEndOfTheStatementToGoToTheNextLineWithWrongHighlight
    for MyType
{
}

This may occur in cases where you implement e.g. TryFrom<U> where U is very templated or deep in some module structure.

Actual behavior

The trait name is highlighted like it's the type name and for is not highlighted like a keyword.

Steps to reproduce

1. Copy the snippet into Sublime
2. Observe errant highlighting

[ehuss]

Thanks for the report. The issue isn't necessarily the very long identifier, but the fact that newlines aren't supported, as in:

impl Foo
for Bar
{}

The cause is that the syntax highlighting rules in Sublime can't cross newlines. The lookahead rule here can't see to the next line.

I'm not sure what the best way is to fix it, but I think it will be rather involved (perhaps by creating additional states?). In general, the use of lookaheads is a bit fragile, particularly around newlines.

[fpdotmonkey]

A really dumb way would be to change how for lines are highlighted, e.g. if the word after for looks like a type and there's no in on that line, then it must be the second line of a impl ... for ... statement