Broken character literal highlighting

[nhatanh002]

When a character literal contains a "region" start pattern ('(','[','{','"'), everything after the start pattern is interpreted as a contained region, and consequently breaks syntax highlighting. After further investigation, the regex used to match character literal is actually incorrect according to the Haskell 2010 language specification (https://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-200002.6), which means most valid character literals aren't highlighted at all, and the \u\<code> pattern while not being a legal character in Haskell, is correctly highlighted.

For example, '[' here breaks everything after it: ) is not highlighted as a delimiter - like its matching (, and showVol is not highlighted as it should've been, like getVol above:

With the addition of a ' and a ], they "close" the bogus "open" token [ and ', and everything is highlighted correctly again:

The character literal highlighting is not even correct!

This is how the plugin defines the way haskellCharacter should've been highlighted, notice that the "characters" inside of the single quotes are highlighted as if they weren't character literals instead, e.g. A is highlighted as a type, 9 as a number, + as an operator, z as normal text:

[maurges]

Oh god it's not just me. The character literals used to work fine, then I took some time off haskell, and now they're broken for both vim and neovim.

[maurges]

Yep, just tested it and it's a regression somewhere between neovim 0.4.1 and neovim 0.6.0. It's got something to do with matching \<', and it's the reason I couldn't fix your MR of this issue. Going to open an issue in neovim.

Update: wow, it's more weird. Apparently \<' was always broken, but something in neovim 0.4.1 fixes matching of chars for haskell specifically. Maybe it's the remnants of default highlighting, I don't know. Here is a small test:

" 'a'
syn match haskellChar "\<'[^'\\]'"
highlight def link haskellChar String

If you open it in nvim and :source %, you will see that 'a' is not highlighted.

Update2: my bad, to make this test file work for both nvim 0.4.1 and 0.6.0 you need to add setlocal iskeyword+='. The search for reproducing continues..

Update3: using \< in a :syn remembers the value of iskeyword at the time of creating the :syn. Since iskeyword is set in "after/ftplugin", it seems it applies too late for syntax definitions.

Update4: I conclude that it broke in neovim 0.6.0 exactly, since in 0.5.1 it works