Use input_patterns & add comments for updating it

autoload/ale/completion.vim

@@ -59,7 +59,8 @@ let s:omni_start_map = {
 \   '<default>': '\v[a-zA-Z$_][a-zA-Z$_0-9]*$',
 \}
 
-" A map of exact characters for triggering LSP completions.
+" 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.
 let s:trigger_character_map = {
 \   '<default>': ['.'],
 \   'typescript': ['.', '''', '"'],

rplugin/python3/deoplete/sources/ale.py

@@ -24,7 +24,13 @@ class Source(Base):
         self.rank = 1000
         self.is_bytepos = True
         self.min_pattern_length = 1
-        self.input_pattern = r'(\.|::|->)\w*$'
+        # Do not forget to update s:trigger_character_map in completion.vim in
+        # updating entries in this map.
+        self.input_patterns = {
+            '_': r'\.\w*$',
+            'rust': r'(\.|::)\w*$',
+            'typescript': r'(\.|\'|")\w*$',
+        }
 
     # Returns an integer for the start position, as with omnifunc.
     def get_complete_position(self, context):

test/python/test_deoplete_source.py

@@ -41,7 +41,11 @@ class DeopleteSourceTest(unittest.TestCase):
         )
 
         self.assertEqual(attributes, {
-            'input_pattern': r'(\.|::|->)\w*$',
+            'input_patterns': {
+                '_': r'\.\w*$',
+                'rust': r'(\.|::)\w*$',
+                'typescript': r'(\.|\'|")\w*$',
+            },
             'is_bytepos': True,
             'mark': '[L]',
             'min_pattern_length': 1,