[ShryukGrandhi]

Summary

In the zsh syntax, an escaped single quote outside of a string (\') was treated as the start of a single-quoted string. Something like

printf 'it'\''s a problem'

left everything after it highlighted as a string until the next ', which could be many lines later. This is the case from the original report (the screenshots are of a zsh file).

Changes

• runtime/syntax/zsh.yaml: add a small constant.specialChar region that starts at a backslash and ends after the next character (or at end of line). This way an escaped quote can't open a string. It is placed before the string regions and only applies outside strings, so a backslash inside '...' still has no special meaning, and a trailing \ used for line continuation doesn't carry over to the next line.
• pkg/highlight/zsh_test.go: regression test that loads zsh.yaml and checks three things: 'it'\''s' is closed on its line, a line-continuation backslash doesn't leak into the next line, and 'a\' ends at its second quote.

The shell (sh.yaml) problems mentioned later in the thread are a separate issue, and this PR doesn't touch them.

Testing

• go test ./pkg/highlight/ -run Zsh -v: fails before the change, passes after
• go test ./...: passes
• gofmt -l pkg/highlight, go vet ./pkg/highlight/: clean

Fixes #1309