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.

test/completion/test_completion_filtering.vader

@@ -140,3 +140,61 @@ Execute(Filtering should respect filetype triggers):
   AssertEqual b:suggestions, ale#completion#Filter(bufnr(''), '', b:suggestions, '.', 0)
   AssertEqual b:suggestions, ale#completion#Filter(bufnr(''), 'rust', b:suggestions, '.', 0)
   AssertEqual b:suggestions, ale#completion#Filter(bufnr(''), 'rust', b:suggestions, '::', 0)
+
+Execute(GetTriggerCharacter should return trigger characters from hardcoded map):
+  AssertEqual '.', ale#completion#GetTriggerCharacter('python', '.')
+  AssertEqual '::', ale#completion#GetTriggerCharacter('rust', '::')
+  AssertEqual '->', ale#completion#GetTriggerCharacter('c', '->')
+  AssertEqual '', ale#completion#GetTriggerCharacter('python', '@')
+
+Execute(GetTriggerCharacter should return empty for empty prefix):
+  AssertEqual '', ale#completion#GetTriggerCharacter('python', '')
+
+Execute(GetTriggerCharacter should use LSP triggers when conn_id provided):
+  call ale#lsp#Register('test-lsp', '/project', '', {})
+  let g:conn_id = 'test-lsp:/project'
+  call ale#lsp#UpdateCapabilities(g:conn_id, {
+  \   'completionProvider': {'triggerCharacters': ['@', '#']},
+  \})
+
+  " '@' is in LSP triggers
+  AssertEqual '@', ale#completion#GetTriggerCharacter('python', '@', g:conn_id)
+  " '.' is NOT in LSP triggers (should not match even though it's in hardcoded)
+  AssertEqual '', ale#completion#GetTriggerCharacter('python', '.', g:conn_id)
+  " '#' is in LSP triggers
+  AssertEqual '#', ale#completion#GetTriggerCharacter('python', '#', g:conn_id)
+
+  call ale#lsp#RemoveConnectionWithID(g:conn_id)
+  unlet g:conn_id
+
+Execute(GetTriggerCharacter should fall back to hardcoded when no LSP triggers):
+  call ale#lsp#Register('test-lsp-empty', '/project', '', {})
+  let g:conn_id = 'test-lsp-empty:/project'
+  call ale#lsp#UpdateCapabilities(g:conn_id, {})
+
+  " Falls back to hardcoded map
+  AssertEqual '.', ale#completion#GetTriggerCharacter('python', '.', g:conn_id)
+  AssertEqual '', ale#completion#GetTriggerCharacter('python', '@', g:conn_id)
+
+  call ale#lsp#RemoveConnectionWithID(g:conn_id)
+  unlet g:conn_id
+
+Execute(Filtering should use LSP trigger characters):
+  call ale#lsp#Register('test-lsp-filter', '/project', '', {})
+  let g:conn_id = 'test-lsp-filter:/project'
+  call ale#lsp#UpdateCapabilities(g:conn_id, {
+  \   'completionProvider': {'triggerCharacters': ['@']},
+  \})
+
+  " Set up completion info with conn_id
+  let b:ale_completion_info = {'conn_id': g:conn_id}
+  let b:suggestions = [{'word': 'foo'}, {'word': 'bar'}]
+
+  " '@' is LSP trigger - should return all suggestions
+  AssertEqual b:suggestions, ale#completion#Filter(bufnr(''), 'python', b:suggestions, '@', 0)
+  " '.' is NOT LSP trigger - should filter
+  AssertEqual [], ale#completion#Filter(bufnr(''), 'python', b:suggestions, '.', 0)
+
+  unlet b:ale_completion_info
+  call ale#lsp#RemoveConnectionWithID(g:conn_id)
+  unlet g:conn_id

test/lsp/test_other_initialize_message_handling.vader

@@ -343,3 +343,51 @@ Execute(Results that are not dictionaries should be handled correctly):
   \ 'result': v:null,
   \})
   AssertEqual [], g:message_list
+
+Execute(GetCompletionTriggerCharacters should return stored characters):
+  call ale#lsp#HandleInitResponse(b:conn, {
+  \ 'jsonrpc': '2.0',
+  \ 'id': 1,
+  \ 'result': {
+  \   'capabilities': {
+  \     'completionProvider': {
+  \       'triggerCharacters': ['@', '#', '.'],
+  \     },
+  \   },
+  \ },
+  \})
+
+  AssertEqual ['@', '#', '.'], ale#lsp#GetCompletionTriggerCharacters(b:conn.id)
+
+Execute(GetCompletionTriggerCharacters should return empty for missing connection):
+  AssertEqual [], ale#lsp#GetCompletionTriggerCharacters('nonexistent-connection')
+
+Execute(GetCompletionTriggerCharacters should return empty when no triggers):
+  call ale#lsp#HandleInitResponse(b:conn, {
+  \ 'jsonrpc': '2.0',
+  \ 'id': 1,
+  \ 'result': {
+  \   'capabilities': {},
+  \ },
+  \})
+
+  AssertEqual [], ale#lsp#GetCompletionTriggerCharacters(b:conn.id)
+
+Execute(GetAllCompletionTriggerCharactersForBuffer should return triggers for open buffers):
+  call ale#lsp#HandleInitResponse(b:conn, {
+  \ 'jsonrpc': '2.0',
+  \ 'id': 1,
+  \ 'result': {
+  \   'capabilities': {
+  \     'completionProvider': {
+  \       'triggerCharacters': ['>', '$'],
+  \     },
+  \   },
+  \ },
+  \})
+
+  call ale#lsp#MarkDocumentAsOpen(b:conn.id, 1)
+  AssertEqual sort(['>', '$']), sort(ale#lsp#GetAllCompletionTriggerCharactersForBuffer(1))
+
+Execute(GetAllCompletionTriggerCharactersForBuffer should return empty for unknown buffer):
+  AssertEqual [], ale#lsp#GetAllCompletionTriggerCharactersForBuffer(99999)