fix(lsp): prefix value sub index and remove symbols in word

Problem:
1. comletion prefix value sub index not correct

2. wrong word generate this will include symbol like -> , it will make compl_match_array build failed

Solution:
1. use max value of server_bounary, word_boundary
2. use vimregex keyword remove unncessary symbols.

runtime/lua/vim/lsp/completion.lua

@@ -154,8 +154,13 @@ local function get_completion_word(item)
       return item.label
     end
   elseif item.textEdit then
-    local word = item.textEdit.newText
+    local word = item.textEdit.newText:gsub('%s+$', '')
-    return word:match('^(%S*)') or word
+    if word:match('^%W') then
+      -- remove unnecessary symbols in label like "->w_locked" => "w_locked"
+      local matched_word = vim.fn.matchstr(word, '\\k\\+')
+      return matched_word ~= '' and matched_word or word
+    end
+    return word
   elseif item.insertText and item.insertText ~= '' then
     return item.insertText
   end
@@ -365,7 +370,8 @@ function M._convert_results(
   elseif curstartbyte ~= nil and curstartbyte ~= server_start_boundary then
     server_start_boundary = client_start_boundary
   end
-  local prefix = line:sub((server_start_boundary or client_start_boundary) + 1, cursor_col)
+  local prefix =
+    line:sub(math.max(server_start_boundary or 0, client_start_boundary) + 1, cursor_col)
   local matches = M._lsp_to_complete_items(result, prefix, client_id)
   return matches, server_start_boundary
 end
@@ -461,7 +467,7 @@ local function trigger(bufnr, clients)
         vim.list_extend(matches, client_matches)
       end
     end
-    local start_col = (server_start_boundary or word_boundary) + 1
+    local start_col = math.max(server_start_boundary or 0, word_boundary) + 1
     vim.fn.complete(start_col, matches)
   end)
 

test/functional/plugin/lsp/completion_spec.lua

@@ -218,6 +218,49 @@ describe('vim.lsp.completion: item conversion', function()
     eq(expected, result)
   end)
 
+  it('removes unnecessary symbols in label', function()
+    local items = {
+      {
+        detail = 'colnr_T',
+        filterText = 'w_virtcol',
+        insertText = '->w_virtcol',
+        insertTextFormat = 1,
+        kind = 5,
+        label = ' w_virtcol',
+        score = 0.59581798315048,
+        sortText = '40e77879w_virtcol',
+        textEdit = {
+          newText = '->w_virtcol',
+          range = {
+            ['end'] = {
+              character = 0,
+              line = 0,
+            },
+            start = {
+              character = 0,
+              line = 0,
+            },
+          },
+        },
+      },
+    }
+    local result = complete('|', items)
+    result = vim.tbl_map(function(x)
+      return {
+        abbr = x.abbr,
+        word = x.word,
+      }
+    end, result.items)
+
+    local expected = {
+      {
+        abbr = ' w_virtcol',
+        word = 'w_virtcol',
+      },
+    }
+    eq(expected, result)
+  end)
+
   it('prefers wordlike components for snippets', function()
     -- There are two goals here:
     --