enhance: undeprecate nvim_lsp and completely remove `nvim` diagnostics source 😉

- Now `nvim_lsp` source shows diagnostics generated by vim.lsp only
  avoids uses vim.diagnostic to avoid deprecation warning on nvim 0.6+
  Why? `vim.lsp.diagnostic` deprecation warnings are way too aggressive.
  And I'm annoyed by people complaining here even though the warning is
  generated by some other plugin (After introduction of nvim_diagnostic
  source lualine just can't produce that warning it used to switch users
  to nvim_diagnostic source with a warning on nvim0.6+).
  Forget it just let anyone that wants lsp specific diagnostics have
  `nvim_lsp` . I'd still recommend using `nvim_diagnostic` over
  `nvim_lsp` as diagnostics generayed by plugins like `null-ls` won't
  showup in `nvim_lsp`
- Remove remanents of `nvim` diagnostics source.

BREAKING_CHANGES.md

@@ -95,3 +95,5 @@ These were hard to understand before. Now the name should convey more info.
 - luae -> lua_expr
 - vimf -> vim_fun
 
+### 'nvim' diagnostic soirce has been renamed to 'nvim_diagnostic'
+What the title says ☝️

lua/lualine/components/diagnostics/init.lua

@@ -53,51 +53,16 @@ function M:init(options)
     }
   end
 
-  -- Error out no source
-  if #self.options.sources < 1 then
-    print('no sources for diagnostics configured')
-    return ''
-  end
-  if vim.fn.has('nvim-0.6') == 1 then
-    for i, name in ipairs(self.options.sources) do
-      if name == 'nvim_lsp' then
-        self.options.sources[i] = 'nvim_diagnostic'
-        modules.utils_notices.add_notice([[
-### diagnostics.source
-Diagnostics source `nvim_lsp` has been deprecated in favour of `nvim_diagnostic`.
-nvim_diagnostic shows diagnostics from neovim's diagnostics api
-while nvim_lsp used to only show lsp diagnostics.
-
-You've something like this your config.
-```lua
-  {'diagnostics', sources = {'nvim_lsp'}}
-```
-It needs to be updated to:
-```lua
-  {'diagnostics', sources = {'nvim_diagnostic'}}
-```
-]])
-      elseif name == 'nvim' then
-        self.options.sources[i] = 'nvim_diagnostic'
-        modules.utils_notices.add_notice([[
-### diagnostics.source
-Diagnostics source `nvim` has been renamed to `nvim_diagnostic`
-
-You've something like this your config.
-```lua
-  {'diagnostics', sources = {'nvim'}}
-```
-It needs to be updated to:
-```lua
-  {'diagnostics', sources = {'nvim_diagnostic'}}
-```
-]])
-      end
-    end
-  end
   -- Initialize variable to store last update so we can use it in insert
   -- mode for no update_in_insert
   self.last_diagnostics_count = {}
+
+  -- Error out no source
+  if #self.options.sources < 1 then
+    modules.utils_notices.add_notice(
+      '### diagnostics.sources\n\nno sources for diagnostics configured.\nPlease specify which diagnostics source you want lualine to use with `sources` option.\n'
+    )
+  end
 end
 
 function M:update_status()

lua/lualine/components/diagnostics/sources.lua

@@ -5,10 +5,29 @@ local M = {}
 ---        info_count:number, hint_count:number
 M.sources = {
   nvim_lsp = function()
-    local error_count = vim.lsp.diagnostic.get_count(0, 'Error')
-    local warning_count = vim.lsp.diagnostic.get_count(0, 'Warning')
-    local info_count = vim.lsp.diagnostic.get_count(0, 'Information')
-    local hint_count = vim.lsp.diagnostic.get_count(0, 'Hint')
+    local error_count, warning_count, info_count, hint_count
+    if vim.fn.has('nvim-0.6') == 1 then
+      -- On nvim 0.6+ use vim.diagnostic to get lsp generated diagnostic count.
+      local diagnostics = vim.diagnostic.get(0)
+      local count = { 0, 0, 0, 0 }
+      for _, diagnostic in ipairs(diagnostics) do
+        if vim.startswith(vim.diagnostic.get_namespace(diagnostic.namespace).name, 'vim.lsp') then
+          count[diagnostic.severity] = count[diagnostic.severity] + 1
+        end
+      end
+      error_count = count[vim.diagnostic.severity.ERROR]
+      warning_count = count[vim.diagnostic.severity.WARN]
+      info_count = count[vim.diagnostic.severity.INFO]
+      hint_count = count[vim.diagnostic.severity.HINT]
+    else
+      -- On 0.5 use older vim.lsp.diagnostic module.
+      -- Maybe we should phase out support for 0.5 though I haven't yet found a solid reason to.
+      -- Eventually this will be removed when 0.5 is no longer supported.
+      error_count = vim.lsp.diagnostic.get_count(0, 'Error')
+      warning_count = vim.lsp.diagnostic.get_count(0, 'Warning')
+      info_count = vim.lsp.diagnostic.get_count(0, 'Information')
+      hint_count = vim.lsp.diagnostic.get_count(0, 'Hint')
+    end
     return error_count, warning_count, info_count, hint_count
   end,
   nvim_diagnostic = function()