fix(completion): use insert_snippet if candidate has tab or newline

Details:
- If LSP candidate is marked as snippet but doesn't look like it (as is
  often the case in `gopls`), then 'mini.completion' inserts candidate's
  text as is. Otherwise snippet insert might "eat" next non-keyword
  character.

  The "looks like snippet" was equivalent to "contains either tabstop or
  variable". However, it is also beneficial to check for newlines and
  tabs, as `snippet_insert` might want to deal with text reindent and
  tab expand.

Resolve #2070

Author: echasnovski

doc/mini-completion.txt

@@ -118,8 +118,8 @@ Notes:
 - To stop LSP server from suggesting snippets, disable (set to `false`) the
   following capability during LSP server start:
   `textDocument.completion.completionItem.snippetSupport`.
-- If snippet body doesn't contain tabstops, `lsp_completion.snippet_insert`
-  is not called and text is inserted as is.
+- If snippet body doesn't contain tabstop, variable, tab, or newline,
+  `lsp_completion.snippet_insert` is not called and text is inserted as-is.
 
 # Notes ~
 

lua/mini/completion.lua

@@ -116,8 +116,8 @@
 --- - To stop LSP server from suggesting snippets, disable (set to `false`) the
 ---   following capability during LSP server start:
 ---   `textDocument.completion.completionItem.snippetSupport`.
---- - If snippet body doesn't contain tabstops, `lsp_completion.snippet_insert`
----   is not called and text is inserted as is.
+--- - If snippet body doesn't contain tabstop, variable, tab, or newline,
+---   `lsp_completion.snippet_insert` is not called and text is inserted as-is.
 ---
 --- # Notes ~
 ---
@@ -1243,11 +1243,14 @@ H.lsp_completion_response_items_to_complete_items = function(items)
 
     local is_snippet_kind = item.kind == snippet_kind
     local is_snippet_format = item.insertTextFormat == snippet_inserttextformat
-    -- Treat item as snippet only if it has tabstops or variables. This is
-    -- important to make "implicit" expand work with LSP servers that report
-    -- even regular words as `InsertTextFormat.Snippet` (like `gopls`).
-    local needs_snippet_insert = (is_snippet_kind or is_snippet_format)
-      and (word:find('[^\\]%${?%w') ~= nil or word:find('^%${?%w') ~= nil)
+    -- Treat item as snippet only if it has tabstop, variable, tab, or newline.
+    -- It is important to make "implicit" expand work with LSP servers that
+    -- report even regular words as `InsertTextFormat.Snippet` (like `gopls`).
+    -- Otherwise it will "eat" the next typed non-keyword charater.
+    -- Account for tabs and newline to allow `snippet_insert` to deal with
+    -- reindenting and tab expansion.
+    local has_snippet_features = (word:find('[^\\]%${?%w') or word:find('^%${?%w') or word:find('[\n\t]')) ~= nil
+    local needs_snippet_insert = (is_snippet_kind or is_snippet_format) and has_snippet_features
 
     local details = item.labelDetails or {}
     -- NOTE: Using `table.concat({}, ' ')` would be cleaner but less performant

tests/screenshots/tests-test_completion.lua---Snippets---are-not-inserted-if-have-no-tabstops-or-variables

@@ -1,6 +1,6 @@
 --|---------|---------|---------|---------|---------|--
 01|                                                    
-02|Just^@text                               Snippet    
+02|Just text                                Snippet    
 03|Text with \$1 escaped dollar             Snippet    
 04|Text with \$TM_FILENAME escaped dollar   Snippet    
 05|Text with \${1} escaped dollar           Snippet    
@@ -15,9 +15,11 @@
 14|Has $0 tabstop                           Snippet S  
 15|Has ${0} tabstop                         Snippet S  
 16|Has tabstop$0                            Snippet S  
-17|~                                                   
-18|[No Name] 0,1                                       
-19|-- INSERT --                                        
+17|Has  tab                                 Snippet S  
+18|Has^@newline                             Snippet S  
+19|~                                                   
+20|[No Name] 0,1                                       
+21|-- INSERT --                                        
 
 --|---------|---------|---------|---------|---------|--
 01|0000000000000000000000000000000000000000000000000000
@@ -36,6 +38,8 @@
 14|1111111111111111111111111111111111111111111111111112
 15|1111111111111111111111111111111111111111111111111112
 16|1111111111111111111111111111111111111111111111111112
-17|2222222222222222222222222222222222222222222222222222
-18|3333333333333333333333333333333333333333333333333333
-19|4444444444445555555555555555555555555555555555555555
+17|1111111111111111111111111111111111111111111111111112
+18|1111111111111111111111111111111111111111111111111112
+19|2222222222222222222222222222222222222222222222222222
+20|3333333333333333333333333333333333333333333333333333
+21|4444444444445555555555555555555555555555555555555555

tests/test_completion.lua

@@ -2557,10 +2557,10 @@ T['Snippets']['are not inserted if have no tabstops or variables'] = function()
   -- Treating text as snippet if there is a variable is important for a snippet
   -- insert method to expand them.
 
-  child.set_size(19, 52)
+  child.set_size(21, 52)
   local snippets = {
     -- - No insert:
-    'Just\ntext',
+    'Just text',
     [[Text with \$1 escaped dollar]],
     [[Text with \$TM_FILENAME escaped dollar]],
     [[Text with \${1} escaped dollar]],
@@ -2576,6 +2576,8 @@ T['Snippets']['are not inserted if have no tabstops or variables'] = function()
     'Has $0 tabstop',
     'Has ${0} tabstop',
     'Has tabstop$0',
+    'Has\ttab',
+    'Has\nnewline',
   }
   mock_lsp_snippets(snippets)