feat(statusline): allow custom signs in section_diagnostics()

Another approach would be to use sign text from
`vim.diagnostic.config().signs.text`. However, it has downsides:
- Users might want to show different severity levels in signcolumn
  and statusline. Not wanting info and hint levels in signcolumn but
  want in statusline seems like a pretty reasonable setup.
- It is only present in Neovim>=0.10. For reverse compatibility, it
  should also use `vim.fn.sign_getdefined()`, which is cumbersome.
- For best performance, some kind of caching should be done (otherwise
  execution time increases from median ~2.6 microseconds to ~4.7).
  Yet it is cumbersome to have it properly updated (and even created)
  without forcing `require('vim.diagnostic')` during startup.

The price to pay for using `args.signs` is that it requires explicit
(possibly duplicating) lines in config via the whole and verbose
`active` content function.

Resolve #769

CHANGELOG.md

@@ -62,6 +62,7 @@
     - Something is shown **only** if there is any diagnostic actually present in the buffer. No diagnostic entries - nothing is shown.
     Previously it did not show if there was no LSP servers attached (as initially diagnostics came only from LSP) or buffer was not normal.
     - Fallback icon is "Diag" instead of "LSP".
+- FEATURE: `section_diagnostics()` now supports `signs` table option to customize signs for severity levels.
 - BREAKING FEATURE: `section_git()` now prefers using data from 'mini.git' with fallback on pure HEAD data from 'lewis6991/gistigns.nvim'.
 - FEATURE: add `section_diff()` to show data from 'mini.diff' with fallback on diff data from 'lewis6991/gistigns.nvim'.
 - FEATURE: add `section_lsp()` to show indicator of LSP servers attached to the buffer.

doc/mini-statusline.txt

@@ -268,6 +268,8 @@ Short output is returned if window width is lower than `args.trunc_width`.
 
 Parameters ~
 {args} `(table)` Section arguments. Use `args.icon` to supply your own icon.
+  Use `args.signs` to use custom signs per severity level name. For example:
+  `{ ERROR = '!', WARN = '?', INFO = '@', HINT = '*' }`
 
 Return ~
 `(string)` Section string.

lua/mini/statusline.lua

@@ -325,18 +325,20 @@ end
 --- Short output is returned if window width is lower than `args.trunc_width`.
 ---
 ---@param args __statusline_args Use `args.icon` to supply your own icon.
+---   Use `args.signs` to use custom signs per severity level name. For example:
+---   `{ ERROR = '!', WARN = '?', INFO = '@', HINT = '*' }`
 ---
 ---@return __statusline_section
 MiniStatusline.section_diagnostics = function(args)
   if MiniStatusline.is_truncated(args.trunc_width) or H.diagnostic_is_disabled() then return '' end
 
   -- Construct string parts
   local count = H.diagnostic_get_count()
-  local severity, t = vim.diagnostic.severity, {}
+  local severity, signs, t = vim.diagnostic.severity, args.signs or {}, {}
   for _, level in ipairs(H.diagnostic_levels) do
     local n = count[severity[level.name]] or 0
     -- Add level info only if diagnostic is present
-    if n > 0 then table.insert(t, ' ' .. level.sign .. n) end
+    if n > 0 then table.insert(t, ' ' .. (signs[level.name] or level.sign) .. n) end
   end
   if #t == 0 then return '' end
 

tests/test_statusline.lua

@@ -336,6 +336,13 @@ T['section_diagnostics()']['respects `args.icon`'] = function()
   eq(child.lua_get([[MiniStatusline.section_diagnostics({icon = 'AAA'})]]), 'AAA E4 W3 I2 H1')
 end
 
+T['section_diagnostics()']['respects `args.signs`'] = function()
+  local out = child.lua_get(
+    [[MiniStatusline.section_diagnostics({ signs = { ERROR = '!', WARN = '?', INFO = '@', HINT = '*' } })]]
+  )
+  eq(out, ' !4 ?3 @2 *1')
+end
+
 T['section_diagnostics()']['respects `config.use_icons`'] = function()
   child.lua('MiniStatusline.config.use_icons = false')
   eq(child.lua_get([[MiniStatusline.section_diagnostics({})]]), 'Diag E4 W3 I2 H1')