Add strip! directive for queries

The strip! directive is implemented in the tree-sitter tags crate in
the main tree-sitter repo
(de53b82e2c/tags/src/lib.rs (L167)).
It is used specifically for tag extraction to shrink the range of a node
(or better the text of a node).

For our textobjects queries the strip! directive might be use full since
it allows us to strip aways whitespaces and leading/trailing characters.

lua/nvim-treesitter/query.lua

@@ -1,5 +1,6 @@
 local api = vim.api
 local ts = vim.treesitter
+local utils = require 'nvim-treesitter.utils'
 
 local M = {}
 
@@ -71,6 +72,56 @@ function M.get_query(lang, query_name)
   end
 end
 
+ --This function is copied from Neovims treesitter.lua to enforece same behavior
+local magic_prefixes = {['\\v']=true, ['\\m']=true, ['\\M']=true, ['\\V']=true}
+local function check_magic(str)
+  if string.len(str) < 2 or magic_prefixes[string.sub(str,1,2)] then
+    return str
+  end
+  return '\\v'..str
+end
+
+local function strip_beginning(lines, regex)
+  local current_col = 0
+  local current_line = 0
+  local re = vim.regex(check_magic('^('..regex..')'))
+  for linenr, line in ipairs(lines) do
+    current_line = linenr
+    local match_start, match_end = re:match_str(line)
+    if match_start ~= 0 then
+      break
+    else
+      current_col = match_end
+    end
+    if match_end ~= vim.str_byteindex(line, #line) then
+      break
+    end
+    current_line = current_line + 1
+  end
+  return current_line - 1, current_col
+end
+
+local function strip_end(lines, regex)
+  local current_col = 0
+  local line_diff = 0
+  local re = vim.regex(check_magic('('..regex..')$'))
+  for linenr=#lines, 1, -1 do
+    local line = lines[linenr]
+    line_diff = #lines - linenr
+    local match_start, match_end = re:match_str(line)
+    if match_end ~= vim.str_byteindex(line, #line) then
+      break
+    else
+      current_col = match_start
+    end
+    if match_start ~= 0 then
+      break
+    end
+    line_diff = line_diff + 1
+  end
+  return line_diff, current_col
+end
+
 function M.iter_prepared_matches(query, qnode, bufnr, start_row, end_row)
   -- A function that splits  a string on '.'
   local function split(string)
@@ -120,6 +171,39 @@ function M.iter_prepared_matches(query, qnode, bufnr, start_row, end_row)
           if pred[1] == "set!" and type(pred[2]) == "string" then
             insert_to_path(prepared_match, split(pred[2]), pred[3])
           end
+          if pred[1] == "strip!" and #pred == 3 then
+            local query_name = query.captures[pred[2]]
+            local regex = pred[3]
+
+            local node = utils.get_at_path(prepared_match, query_name..'.node')
+            local ts_utils = require 'nvim-treesitter.ts_utils'
+            local node_lines = ts_utils.get_node_text(node, bufnr)
+            local start_line, start_col, end_line, end_col = node:range()
+
+            local strip_line, strip_col = strip_beginning(node_lines, regex)
+            start_line = start_line + strip_line
+            if strip_line == 0 then
+              start_col = start_col + strip_col
+            else
+              start_col =strip_col
+            end
+            local strip_line, strip_col = strip_end(node_lines, regex)
+            end_line = end_line - strip_line
+            if strip_line == 0 then
+              end_col = end_col - strip_col
+            else
+              end_col = strip_col
+            end
+
+            end_line = math.max(end_line, start_line)
+            if end_line == start_line then
+              end_col = math.max(end_col, start_col)
+            end
+
+            insert_to_path(prepared_match,
+                           split(query_name..'.processed_range'),
+                           {start_line, start_col, end_line, end_col})
+          end
         end
       end