feat(lsp): Split out a diagnostics_to_items function from set_loclist

Makes it easier to re-use the logic to populate the quickfix list
instead of the location list.

runtime/lua/vim/lsp/util.lua

@@ -30,6 +30,16 @@ local default_border = {
   {" ", "NormalFloat"},
 }
 
+
+local DiagnosticSeverity = protocol.DiagnosticSeverity
+local loclist_type_map = {
+  [DiagnosticSeverity.Error] = 'E',
+  [DiagnosticSeverity.Warning] = 'W',
+  [DiagnosticSeverity.Information] = 'I',
+  [DiagnosticSeverity.Hint] = 'I',
+}
+
+
 --@private
 -- Check the border given by opts or the default border for the additional
 -- size it adds to a float.
@@ -1878,6 +1888,40 @@ function M.lookup_section(settings, section)
   return settings
 end
 
+
+--- Convert diagnostics grouped by bufnr to a list of items for use in the
+--- quickfix or location list.
+---
+--@param diagnostics_by_bufnr table bufnr -> Diagnostic[]
+--@param predicate an optional function to filter the diagnostics.
+--                  If present, only diagnostic items matching will be included.
+--@return table (A list of items)
+function M.diagnostics_to_items(diagnostics_by_bufnr, predicate)
+  local items = {}
+  for bufnr, diagnostics in pairs(diagnostics_by_bufnr or {}) do
+    for _, d in pairs(diagnostics) do
+      if not predicate or predicate(d) then
+        table.insert(items, {
+          bufnr = bufnr,
+          lnum = d.range.start.line + 1,
+          col = d.range.start.character + 1,
+          text = d.message,
+          type = loclist_type_map[d.severity or DiagnosticSeverity.Error] or 'E'
+        })
+      end
+    end
+  end
+  table.sort(items, function(a, b)
+    if a.bufnr == b.bufnr then
+      return a.lnum < b.lnum
+    else
+      return a.bufnr < b.bufnr
+    end
+  end)
+  return items
+end
+
+
 M._get_line_byte_from_position = get_line_byte_from_position
 M._warn_once = warn_once