fix(render): handle large messages when calculating line width

Some misbehaving plugin code was sending very large messages to
`vim.notify()`, which would trigger an exception when calculating the
max line width for rendering:

```
[...]/notify/render/default.lua:6: too many results to unpack
```

To fix this, I updated the implementation to calculate the max line
width in-place. This ultimately ends up being much more efficient because
it is not creating a new table with `vim.tbl_map()`.

Here's some benchmark data:
https://gist.github.com/flrgh/349aecd8ca35d20cf0526ec8b218657c

In the large input benchmarks, the new function is ~2x faster. For small
inputs (which are probably most common for `vim.notify()`), the speedup
is even larger at 3-4x.

Other changes:

  1. I noticed the same snippet appeared in multiple render modules, so
     I factored it out into `notify.util.max_line_width()` and added a
     unit test
  2. I updated the calculation to use `vim.api.nvim_strwidth()` when
     available (see #247).

lua/notify/render/default.lua

@@ -1,11 +1,11 @@
 local api = vim.api
 local base = require("notify.render.base")
+local util = require("notify.util")
 
 return function(bufnr, notif, highlights, config)
   local left_icon = notif.icon .. " "
-  local max_message_width = math.max(math.max(unpack(vim.tbl_map(function(line)
-    return vim.fn.strchars(line)
-  end, notif.message))))
+  local max_message_width = util.max_line_width(notif.message)
+
   local right_title = notif.title[2]
   local left_title = notif.title[1]
   local title_accum = vim.str_utfindex(left_icon)

lua/notify/render/simple.lua

@@ -1,10 +1,10 @@
 local api = vim.api
 local base = require("notify.render.base")
+local util = require("notify.util")
 
 return function(bufnr, notif, highlights, config)
-  local max_message_width = math.max(math.max(unpack(vim.tbl_map(function(line)
-    return vim.fn.strchars(line)
-  end, notif.message))))
+  local max_message_width = util.max_line_width(notif.message)
+
   local title = notif.title[1]
   local title_accum = vim.str_utfindex(title)
 

lua/notify/util/init.lua

@@ -2,6 +2,8 @@ local M = {}
 
 local min, max, floor = math.min, math.max, math.floor
 local rshift, lshift, band, bor = bit.rshift, bit.lshift, bit.band, bit.bor
+local strwidth = vim.api.nvim_strwidth or vim.fn.strchars
+
 function M.is_callable(obj)
   return type(obj) == "function" or (type(obj) == "table" and obj.__call)
 end
@@ -117,4 +119,19 @@ function M.highlight(name, fields)
   end
 end
 
+--- Calculate the max render width of a message
+---@param msg string[]|nil
+---@return integer
+function M.max_line_width(msg)
+  local width = 0
+
+  if msg then
+    for i = 1, #msg do
+      width = max(width, strwidth(msg[i]))
+    end
+  end
+
+  return width
+end
+
 return M

tests/unit/init_spec.lua

@@ -157,4 +157,18 @@ describe("checking public interface", function()
     a.util.scheduler()
     assert(vim.api.nvim_win_is_valid(win))
   end)
+
+  describe("util", function()
+    local util = require("notify.util")
+
+    describe("max_line_width()", function()
+      it("returns the maximal width of a table of lines", function()
+        assert.equals(5, util.max_line_width({ "12", "12345", "123" }))
+      end)
+
+      it("returns 0 for nil input", function()
+        assert.equals(0, util.max_line_width())
+      end)
+    end)
+  end)
 end)