Read trigger characters from LSP initialize responses (#5121)

* Add ale#lsp#GetCompletionTriggerCharacters getter
* Add s:GetTriggerCharacters helper with LSP support
* Pass connection ID to GetTriggerCharacter in s:OnReady
* Use LSP trigger characters in Filter function
* Add tests for LSP completion trigger characters
* Check LSP trigger characters in GetPrefix
* Add tests for GetAllCompletionTriggerCharactersForBuffer

GetTriggerCharacter now accepts optional conn_id parameter to
prefer LSP-provided trigger characters over the hardcoded map.

GetPrefix now checks if the line ends with any trigger character
from LSPs active for the current buffer, enabling automatic
completion for LSP-provided triggers like > for PHP.

autoload/ale/completion.vim

@@ -145,6 +145,7 @@ let s:omni_start_map = {
 
 " A map of exact characters for triggering LSP completions. Do not forget to
 " update self.input_patterns in ale.py in updating entries in this map.
+" These are used as a fallback when LSP servers don't provide trigger chars.
 let s:trigger_character_map = {
 \   '<default>': ['.'],
 \   'typescript': ['.', '''', '"'],
@@ -153,6 +154,19 @@ let s:trigger_character_map = {
 \   'c': ['.', '->'],
 \}
 
+" Get trigger characters, preferring LSP-provided ones over hardcoded.
+function! s:GetTriggerCharacters(filetype, conn_id) abort
+    if !empty(a:conn_id)
+        let l:lsp_triggers = ale#lsp#GetCompletionTriggerCharacters(a:conn_id)
+
+        if !empty(l:lsp_triggers)
+            return l:lsp_triggers
+        endif
+    endif
+
+    return s:GetFiletypeValue(s:trigger_character_map, a:filetype)
+endfunction
+
 function! s:GetFiletypeValue(map, filetype) abort
     for l:part in reverse(split(a:filetype, '\.'))
         let l:regex = get(a:map, l:part, [])
@@ -175,15 +189,32 @@ function! ale#completion#GetPrefix(filetype, line, column) abort
     "   abc
     "      ^
     " So we need check the text in the column before that position.
-    return matchstr(getline(a:line)[: a:column - 2], l:regex)
+    let l:line_text = getline(a:line)[: a:column - 2]
+    let l:prefix = matchstr(l:line_text, l:regex)
+
+    if !empty(l:prefix)
+        return l:prefix
+    endif
+
+    " Check LSP trigger characters for active connections on this buffer.
+    let l:triggers = ale#lsp#GetAllCompletionTriggerCharactersForBuffer(bufnr(''))
+
+    for l:char in l:triggers
+        if l:line_text[-len(l:char):] is# l:char
+            return l:char
+        endif
+    endfor
+
+    return ''
 endfunction
 
-function! ale#completion#GetTriggerCharacter(filetype, prefix) abort
+function! ale#completion#GetTriggerCharacter(filetype, prefix, ...) abort
     if empty(a:prefix)
         return ''
     endif
 
-    let l:char_list = s:GetFiletypeValue(s:trigger_character_map, a:filetype)
+    let l:conn_id = get(a:, 1, '')
+    let l:char_list = s:GetTriggerCharacters(a:filetype, l:conn_id)
 
     if index(l:char_list, a:prefix) >= 0
         return a:prefix
@@ -204,7 +235,8 @@ function! ale#completion#Filter(
     if empty(a:prefix)
         let l:filtered_suggestions = a:suggestions
     else
-        let l:triggers = s:GetFiletypeValue(s:trigger_character_map, a:filetype)
+        let l:conn_id = get(get(b:, 'ale_completion_info', {}), 'conn_id', '')
+        let l:triggers = s:GetTriggerCharacters(a:filetype, l:conn_id)
 
         " For completing...
         "   foo.
@@ -805,7 +837,7 @@ function! s:OnReady(linter, lsp_details) abort
         \   l:buffer,
         \   b:ale_completion_info.line,
         \   b:ale_completion_info.column,
-        \   ale#completion#GetTriggerCharacter(&filetype, b:ale_completion_info.prefix),
+        \   ale#completion#GetTriggerCharacter(&filetype, b:ale_completion_info.prefix, l:id),
         \)
     endif
 

autoload/ale/lsp.vim

@@ -1010,3 +1010,33 @@ function! ale#lsp#HasCapability(conn_id, capability) abort
 
     return l:conn.capabilities[a:capability]
 endfunction
+
+" Get the completion trigger characters for a connection.
+function! ale#lsp#GetCompletionTriggerCharacters(conn_id) abort
+    let l:conn = get(s:connections, a:conn_id, {})
+
+    if empty(l:conn)
+        return []
+    endif
+
+    return get(l:conn.capabilities, 'completion_trigger_characters', [])
+endfunction
+
+" Get all completion trigger characters from LSPs active for a buffer.
+function! ale#lsp#GetAllCompletionTriggerCharactersForBuffer(buffer) abort
+    let l:all_triggers = []
+
+    for l:conn in values(s:connections)
+        if has_key(l:conn.open_documents, a:buffer)
+            let l:triggers = get(l:conn.capabilities, 'completion_trigger_characters', [])
+
+            for l:char in l:triggers
+                if index(l:all_triggers, l:char) < 0
+                    call add(l:all_triggers, l:char)
+                endif
+            endfor
+        endif
+    endfor
+
+    return l:all_triggers
+endfunction