feat(#1917): add diagnostic highlighting and icon placement (#2396)

* feat(#1917): add renderer.highlight_diagnostics

* feat(#1917): add renderer.highlight_diagnostics

* feat(#1917): add enderer.icons.diagnostics_placement

* feat(#1917): add renderer.icons.show.diagnostics

* feat(#1917): document highlight overrides

lua/nvim-tree/renderer/components/diagnostics.lua

@@ -0,0 +1,58 @@
+local M = {}
+
+local H = {}
+local I = {}
+
+---diagnostics text highlight group if there is a status
+---@param node table
+---@return string|nil highlight
+function M.get_highlight(node)
+  if M.config.diagnostics.enable and M.config.renderer.highlight_diagnostics then
+    return H[node.diag_status]
+  end
+end
+
+---diagnostics icon if there is a status
+---@param node table
+---@return HighlightedString|nil modified icon
+function M.get_icon(node)
+  if M.config.diagnostics.enable and M.config.renderer.icons.show.diagnostics then
+    return I[node.diag_status]
+  end
+end
+
+function M.setup(opts)
+  M.config = {
+    diagnostics = opts.diagnostics,
+    renderer = opts.renderer,
+  }
+
+  H[vim.diagnostic.severity.ERROR] = "NvimTreeLspDiagnosticsErrorText"
+  H[vim.diagnostic.severity.WARN] = "NvimTreeLspDiagnosticsWarningText"
+  H[vim.diagnostic.severity.INFO] = "NvimTreeLspDiagnosticsInfoText"
+  H[vim.diagnostic.severity.HINT] = "NvimTreeLspDiagnosticsHintText"
+
+  I[vim.diagnostic.severity.ERROR] = {
+    str = M.config.diagnostics.icons.error,
+    hl = "NvimTreeLspDiagnosticsError",
+  }
+
+  I[vim.diagnostic.severity.WARN] = {
+    str = M.config.diagnostics.icons.warning,
+    hl = "NvimTreeLspDiagnosticsWarning",
+  }
+  I[vim.diagnostic.severity.INFO] = {
+    str = M.config.diagnostics.icons.info,
+    hl = "NvimTreeLspDiagnosticsInfo",
+  }
+  I[vim.diagnostic.severity.HINT] = {
+    str = M.config.diagnostics.icons.hint,
+    hl = "NvimTreeLspDiagnosticsHint",
+  }
+
+  for _, i in ipairs(I) do
+    vim.fn.sign_define(i.hl, { text = i.str, texthl = i.hl })
+  end
+end
+
+return M