feat: add vim.str_utf_{start,end} (#16129)

vim.str_utf_{start,end} return the offset from the current position to
the start and end of the current utf-character (nearest codepoint)
respectively.

1 files changed, 25 insertions, 0 deletions

diff --git a/test/functional/lua/vim_spec.lua b/test/functional/lua/vim_spec.lua
index 8c691b1121..5f903e7d5f 100644
--- a/test/functional/lua/vim_spec.lua
+++ b/test/functional/lua/vim_spec.lua
@@ -179,6 +179,31 @@ describe('lua stdlib', function()
     end
   end)
 
+  it("vim.str_utf_start", function()
+    exec_lua([[_G.test_text = "xy åäö ɧ 汉语 ↥ 🤦x🦄 å بِيَّ"]])
+    local expected_positions = {0,0,0,0,-1,0,-1,0,-1,0,0,-1,0,0,-1,-2,0,-1,-2,0,0,-1,-2,0,0,-1,-2,-3,0,0,-1,-2,-3,0,0,0,-1,0,0,-1,0,-1,0,-1,0,-1,0,-1}
+    eq(expected_positions, exec_lua([[
+      local start_codepoint_positions = {}
+      for idx = 1, #_G.test_text do
+        table.insert(start_codepoint_positions, vim.str_utf_start(_G.test_text, idx))
+      end
+      return start_codepoint_positions
+    ]]))
+  end)
+
+  it("vim.str_utf_end", function()
+    exec_lua([[_G.test_text = "xy åäö ɧ 汉语 ↥ 🤦x🦄 å بِيَّ"]])
+    local expected_positions = {0,0,0,1,0,1,0,1,0,0,1,0,0,2,1,0,2,1,0,0,2,1,0,0,3,2,1,0,0,3,2,1,0,0,0,1,0,0,1,0,1,0,1,0,1,0,1,0 }
+    eq(expected_positions, exec_lua([[
+      local end_codepoint_positions = {}
+      for idx = 1, #_G.test_text do
+        table.insert(end_codepoint_positions, vim.str_utf_end(_G.test_text, idx))
+      end
+      return end_codepoint_positions
+    ]]))
+  end)
+
+
   it("vim.str_utf_pos", function()
     exec_lua([[_G.test_text = "xy åäö ɧ 汉语 ↥ 🤦x🦄 å بِيَّ"]])
     local expected_positions = { 1,2,3,4,6,8,10,11,13,14,17,20,21,24,25,29,30,34,35,36,38,39,41,43,45,47 }