:set ft=help triggers error in :h syntax.txt (E969)

[habamax]

Steps to reproduce

1. vim -Nu NONE
2. :syntax on
3. :h cursorlinefold

UPD:

1. vim -Nu NONE
2. :syntax on
3. :h syntax.txt
4. :set ft=help

Expected behaviour

Help window should be opened without error.

Version of Vim

8.2.4939

Environment

Fedora 36, all terminals

Logs and stack traces

No response

[habamax]

[Shane-XB-Qian]

VIM - Vi IMproved 8.2 (2019 Dec 12, compiled May 12 2022 15:21:35)
Included patches: 1-4939

no err to me. :-)

[lacygoill]

I don't have any error, but this silent! should fix the issue:

diff --git a/runtime/import/dist/vimhelp.vim b/runtime/import/dist/vimhelp.vim
index 1f587251b..7d1e650c2 100644
--- a/runtime/import/dist/vimhelp.vim
+++ b/runtime/import/dist/vimhelp.vim
@@ -9,7 +9,7 @@ export def HighlightGroups()
   while getline(lnum) !~ '===' && lnum < line('$')
     var word: string = getline(lnum)->matchstr('^\w\+\ze\t')
     if word->hlexists()
-      prop_type_add('help-hl-' .. word, {
+      silent! prop_type_add('help-hl-' .. word, {
 	bufnr: buf,
 	highlight: word,
 	combine: false,

Alternatively, we could test the existence of the text property before trying to install it:

diff --git a/runtime/import/dist/vimhelp.vim b/runtime/import/dist/vimhelp.vim
index 1f587251b..9c6cbac5d 100644
--- a/runtime/import/dist/vimhelp.vim
+++ b/runtime/import/dist/vimhelp.vim
@@ -9,11 +9,13 @@ export def HighlightGroups()
   while getline(lnum) !~ '===' && lnum < line('$')
     var word: string = getline(lnum)->matchstr('^\w\+\ze\t')
     if word->hlexists()
-      prop_type_add('help-hl-' .. word, {
-	bufnr: buf,
-	highlight: word,
-	combine: false,
-	})
+      if prop_type_list({bufnr: buf})->index('help-hl-' .. word) == -1
+	prop_type_add('help-hl-' .. word, {
+	  bufnr: buf,
+	  highlight: word,
+	  combine: false,
+	  })
+      endif
       prop_add(lnum, 1, {length: word->strlen(), type: 'help-hl-' .. word})
     endif
     ++lnum

BTW, the code could be improved in several ways. I'll try to open a PR in a few days to suggest some of them.

[habamax]

I have tried it on gvim (windows) with 8.2.4937 and get the same error.

Looks like my configuration is still involved even though I run it with gvim -Nu NONE.

[habamax]

So indeed my configuration interferes, I have ~/.vim/ftdetect/rst.vim that does:

autocmd BufNewFile,BufRead *.txt,*.rest set ft=rst

And this triggers the error mentioned in the OP.

PS, it doesn't matter what filetype I set, the same happens if I set ft=text.

[lacygoill]

autocmd BufNewFile,BufRead .txt,.rest set ft=rst

The :set ft command must probably cause Syntax to be fired a second time, which causes the text property to be installed a second time, which Vim doesn't like:

vim9script
prop_type_add('help-hl-ColorColumn', {highlight: 'ErrorMsg'})
prop_type_add('help-hl-ColorColumn', {highlight: 'ErrorMsg'})

E969: Property type help-hl-ColorColumn already defined

[habamax]

Maybe I should be setting rst filetype only for txt files outside of doc/ dir, but I have my docs in txt files in a ~/doc dir :)

[habamax]

Okay, I think this could be workarounded with the following:

autocmd BufNewFile,BufRead *.txt if &buftype != "help" | set ft=rst | endif

[habamax]

Still, it would be nice if :set ft=help didn't trigger this error in :h syntax.txt

[habamax]

The actual repro steps are:

1. vim -Nu NONE
2. :syntax on
3. :h syntax.txt
4. :set ft=help

[lacygoill]

Yes, this is definitely a bug. Either we should suppress the error with silent!, or check its existence before trying to install it. That's what I always do whenever I install a new text property type, because I never care about this error.

[brammool]

Using silent! may hide other errors. I'll add a check if the type already exists.