(mini.starter) Optimize computation of whether something is shown.

Details:
- Resolves #680.
- Resolves #681.

Author: echasnovski

lua/mini/starter.lua

@@ -1439,13 +1439,8 @@ end
 H.is_something_shown = function()
   -- Don't open Starter buffer if Neovim is opened to show something. That is
   -- when at least one of the following is true:
-  -- - Current buffer has any lines (something opened explicitly).
-  -- NOTE: Usage of `line2byte(line('$') + 1) < 0` seemed to be fine, but it
-  -- doesn't work if some automated changed was made to buffer while leaving it
-  -- empty (returns 2 instead of -1). This was also the reason of not being
-  -- able to test with child Neovim process from 'tests/helpers'.
-  local lines = vim.api.nvim_buf_get_lines(0, 0, -1, true)
-  if #lines > 1 or (#lines == 1 and lines[1]:len() > 0) then return true end
+  -- - There are files in arguments (like `nvim foo.txt` with new file).
+  if vim.fn.argc() > 0 then return true end
 
   -- - Several buffers are listed (like session with placeholder buffers). That
   --   means unlisted buffers (like from `nvim-tree`) don't affect decision.
@@ -1455,8 +1450,15 @@ H.is_something_shown = function()
   )
   if #listed_buffers > 1 then return true end
 
-  -- - There are files in arguments (like `nvim foo.txt` with new file).
-  if vim.fn.argc() > 0 then return true end
+  -- - Current buffer has any lines (something opened explicitly).
+  -- NOTE: Usage of `line2byte(line('$') + 1) < 0` seemed to be fine, but it
+  -- doesn't work if some automated changed was made to buffer while leaving it
+  -- empty (returns 2 instead of -1). This was also the reason of not being
+  -- able to test with child Neovim process from 'tests/helpers'.
+  local n_lines = vim.api.nvim_buf_line_count(0)
+  if n_lines > 1 then return true end
+  local first_line = vim.api.nvim_buf_get_lines(0, 0, 1, true)[1]
+  if string.len(first_line) > 0 then return true end
 
   return false
 end

tests/test_starter.lua

@@ -1100,8 +1100,8 @@ end
 T['Autoopening']['does not autoopen if Neovim started to show something'] = function()
   local init_autoopen = 'tests/dir-starter/init-files/test-init.lua'
 
-  -- Current buffer has any lines (something opened explicitly)
-  child.restart({ '-u', init_autoopen, '-c', [[call setline(1, 'a')]] })
+  -- There are files in arguments (like `nvim foo.txt` with new file).
+  child.restart({ '-u', init_autoopen, 'new-file.txt' })
   validate_starter_not_shown()
 
   -- Several buffers are listed (like session with placeholder buffers)
@@ -1112,8 +1112,8 @@ T['Autoopening']['does not autoopen if Neovim started to show something'] = func
   child.restart({ '-u', init_autoopen, '-c', 'e foo | set nobuflisted | e bar | set buflisted' })
   validate_starter_shown()
 
-  -- There are files in arguments (like `nvim foo.txt` with new file).
-  child.restart({ '-u', init_autoopen, 'new-file.txt' })
+  -- Current buffer has any lines (something opened explicitly)
+  child.restart({ '-u', init_autoopen, '-c', [[call setline(1, 'a')]] })
   validate_starter_not_shown()
 end