feat(diagnostics): emulate VSCode Error Lens with virtual text and lines

	Added functionality to mimic VSCode's Error Lens behavior:
	- Displays diagnostics as virtual text with severity icons during insert mode.
	- Switches to virtual lines with formatted messages in normal mode for better readability.

	Improves real-time feedback while coding and enhances the visual presentation of diagnostics.

Author: glaulher

init.lua

@@ -628,32 +628,54 @@ require('lazy').setup({
 
       -- Diagnostic Config
       -- See :help vim.diagnostic.Opts
-      vim.diagnostic.config {
-        severity_sort = true,
-        float = { border = 'rounded', source = 'if_many' },
-        underline = { severity = vim.diagnostic.severity.ERROR },
-        signs = vim.g.have_nerd_font and {
-          text = {
-            [vim.diagnostic.severity.ERROR] = '󰅚 ',
-            [vim.diagnostic.severity.WARN] = '󰀪 ',
-            [vim.diagnostic.severity.INFO] = '󰋽 ',
-            [vim.diagnostic.severity.HINT] = '󰌶 ',
-          },
-        } or {},
-        virtual_text = {
-          source = 'if_many',
-          spacing = 2,
-          format = function(diagnostic)
-            local diagnostic_message = {
-              [vim.diagnostic.severity.ERROR] = diagnostic.message,
-              [vim.diagnostic.severity.WARN] = diagnostic.message,
-              [vim.diagnostic.severity.INFO] = diagnostic.message,
-              [vim.diagnostic.severity.HINT] = diagnostic.message,
-            }
-            return diagnostic_message[diagnostic.severity]
-          end,
-        },
-      }
+      -- Diagnostic configuration similar to VS Code's Error Lens.
+      -- In insert mode, diagnostics are displayed as inline virtual text.
+      -- In normal mode, diagnostics are shown as virtual lines below the affected lines.
+
+      local function set_virtual_text(enable)
+        local diagnostic_icons = {
+          [vim.diagnostic.severity.ERROR] = '󰅚 ',
+          [vim.diagnostic.severity.WARN] = '󰀪 ',
+          [vim.diagnostic.severity.INFO] = '󰋽 ',
+          [vim.diagnostic.severity.HINT] = '󰌶 ',
+        }
+
+        vim.diagnostic.config {
+          update_in_insert = true, -- error messages in insert mode
+          severity_sort = true,
+          float = { border = 'rounded', source = 'if_many' },
+          underline = { severity = vim.diagnostic.severity.ERROR },
+          signs = vim.g.have_nerd_font and {
+            text = diagnostic_icons,
+          } or {},
+
+          virtual_lines = not enable and {
+            format = function(diagnostic)
+              return (diagnostic_icons[diagnostic.severity] or '') .. diagnostic.message
+            end,
+          } or false,
+
+          virtual_text = enable and {
+            source = 'if_many',
+            spacing = 2,
+            format = function(diagnostic)
+              return (diagnostic_icons[diagnostic.severity] or '') .. diagnostic.message
+            end,
+          } or false,
+        }
+      end
+
+      vim.api.nvim_create_autocmd('InsertEnter', {
+        callback = function()
+          set_virtual_text(true)
+        end,
+      })
+
+      vim.api.nvim_create_autocmd('InsertLeave', {
+        callback = function()
+          set_virtual_text(false)
+        end,
+      })
 
       -- LSP servers and clients are able to communicate to each other what features they support.
       --  By default, Neovim doesn't support everything that is in the LSP specification.