fix: Multi byte truncate for displayer (#464)

This is needed for calling strdisplaywidth() from Lua loop.

See https://github.com/nvim-telescope/telescope.nvim/issues/414
See https://github.com/neovim/neovim/blob/a1ed941a7881122fda2fd48e71e890ed55e4d08e/src/nvim/eval/funcs.c#L9845-L9858

Co-authored-by: Simon Hauser <Simon-Hauser@outlook.de>

1 files changed, 32 insertions, 0 deletions

diff --git a/lua/tests/automated/entry_display_spec.lua b/lua/tests/automated/entry_display_spec.lua
new file mode 100644
index 0000000..fff78cd
--- /dev/null
+++ b/lua/tests/automated/entry_display_spec.lua
@@ -0,0 +1,32 @@
+local entry_display = require('telescope.pickers.entry_display')
+
+describe('truncate', function()
+  for _, ambiwidth in ipairs{'single', 'double'} do
+    for _, case in ipairs{
+      {args = {'abcde', 6}, expected = {single = 'abcde', double = 'abcde'}},
+      {args = {'abcde', 5}, expected = {single = 'abcde', double = 'abcde'}},
+      {args = {'abcde', 4}, expected = {single = 'abc…', double = 'ab…'}},
+      {args = {'アイウエオ', 11}, expected = {single = 'アイウエオ', double = 'アイウエオ'}},
+      {args = {'アイウエオ', 10}, expected = {single = 'アイウエオ', double = 'アイウエオ'}},
+      {args = {'アイウエオ', 9}, expected = {single = 'アイウエ…', double = 'アイウ…'}},
+      {args = {'アイウエオ', 8}, expected = {single = 'アイウ…', double = 'アイウ…'}},
+      {args = {'├─┤', 7}, expected = {single = '├─┤', double = '├─┤'}},
+      {args = {'├─┤', 6}, expected = {single = '├─┤', double = '├─┤'}},
+      {args = {'├─┤', 5}, expected = {single = '├─┤', double = '├…'}},
+      {args = {'├─┤', 4}, expected = {single = '├─┤', double = '├…'}},
+      {args = {'├─┤', 3}, expected = {single = '├─┤', double = '…'}},
+      {args = {'├─┤', 2}, expected = {single = '├…', double = '…'}},
+    } do
+      local msg = ('can truncate: ambiwidth = %s, [%s, %d] -> %s'):format(ambiwidth, case.args[1], case.args[2], case.expected[ambiwidth])
+      it(msg, function()
+        local original = vim.o.ambiwidth
+        vim.o.ambiwidth = ambiwidth
+        assert.are.same(
+          case.expected[ambiwidth],
+          entry_display.truncate(case.args[1], case.args[2])
+        )
+        vim.o.ambiwidth = original
+      end)
+    end
+  end
+end)