For *.rs.erb, set eruby_subtype to "rust"

plugin/holtrop.lua

@@ -102,3 +102,14 @@ vim.api.nvim_create_autocmd({ "FocusGained", "BufEnter" }, {
 })
 
 vim.filetype.add({filename = {["Rsconscript"] = "ruby"}})
+
+-- Treat *.rs.erb files as eruby with an embedded Rust subtype
+vim.filetype.add({
+  pattern = {
+    [".*%.rs%.erb"] = function(_, bufnr)
+      return "eruby", function()
+        vim.b[bufnr].eruby_subtype = "rust"
+      end
+    end,
+  },
+})