Haskell support is thwarted by vscode-haskell

[jamesohortle]

Haskell support is being implemented in branch haskell.

As with other languages, a language support extension that interacts with a language server is required for parsing of source files. In this case, vscode-haskell and haskell-language-server are needed.

Unfortunately, the language extension's hovers appear to blocking ours.

Consider the following test file (src/test/test.hs):

module Main where

import Lib ()

main :: IO ()
{-
 - U+0000 -> Null.
 - U+0020 ->  Space.
 - U+1234 -> ሴ Ethiopic Syllable See.
 - U+0B87 -> இ Tamil Letter I.
 - U+0FDA -> ࿚ Tibetan Mark Trailing Mchan Rtags.
 - U+50B7 -> 傷 Ideograph wound, injury; fall ill from CJK.
 - U+1F639 -> 😹 Cat Face with Tears of Joy.
 - \0000
-}

main =
  putStrLn "\0000"

In Output, under Haskell (UnicodeHover) we can see the below when we hover over putStrLn's argument.

2020-09-09 22:13:09.250435 [ThreadId 207] - Hover request at position 18:15 in file: /Users/jim/UnicodeHover/src/test/test.hs
2020-09-09 22:13:12.031032 [ThreadId 195] - finish: CodeAction (took 0.00s)
2020-09-09 22:13:12.03127 [ThreadId 195] - finish: CodeAction:PackageExports (took 0.00s)
2020-09-09 22:13:17.739479 [ThreadId 213] - DocumentHighlight request at position 14:9 in file: /Users/jim/UnicodeHover/src/test/test.hs
2020-09-09 22:13:17.977093 [ThreadId 195] - finish: CodeAction (took 0.00s)
2020-09-09 22:13:17.97733 [ThreadId 195] - finish: CodeAction:PackageExports (took 0.00s)
2020-09-09 22:18:04.452604 [ThreadId 219] - GhcIde.hover entered (ideLogger)
2020-09-09 22:18:04.452924 [ThreadId 219] - Hover request at position 18:14 in file: /Users/jim/UnicodeHover/src/test/test.hs

The first and last lines of the log above indicate that vscode-haskell is indeed parsing the files correctly, but appears to be blocking UnicodeHover from adding a hover panel.

The output looks like this:

If we hover over the comment, the UnicodeHover panels do appear, but they are displaced all the way above the start of the comment.

We should get in touch with the vscode-haskell team to figure out how to fix this.

[jamesohortle]

The first issue is resolved in commit ecb82cc (glass houses...).

But the second issue remains.

For now, let's implement single character escapes, ASCII control code abbreviations and control-with-character escapes. See here for tables, or the test.hs file.