add runtime warnings for stale files

internal/bootstrap.cm

@@ -48,6 +48,41 @@ if (use_mcode) {
   mcode_mod = boot_load("mcode", boot_env)
 }
 
+// Warn if any .cm source is newer than its .mach bytecode
+function check_mach_stale() {
+  var pairs = [
+    ["tokenize.cm", "tokenize.mach"],
+    ["parse.cm", "parse.mach"],
+    ["fold.cm", "fold.mach"],
+    ["mcode.cm", "mcode.mach"],
+    ["internal/bootstrap.cm", "internal/bootstrap.mach"],
+    ["internal/engine.cm", "internal/engine.mach"]
+  ]
+  var stale = []
+  var _i = 0
+  var cm_path = null
+  var mach_path = null
+  var cm_stat = null
+  var mach_stat = null
+  while (_i < length(pairs)) {
+    cm_path = core_path + '/' + pairs[_i][0]
+    mach_path = core_path + '/' + pairs[_i][1]
+    if (fd.is_file(cm_path) && fd.is_file(mach_path)) {
+      cm_stat = fd.stat(cm_path)
+      mach_stat = fd.stat(mach_path)
+      if (cm_stat.mtime > mach_stat.mtime) {
+        push(stale, pairs[_i][0])
+      }
+    }
+    _i = _i + 1
+  }
+  if (length(stale) > 0) {
+    print("warning: bytecode is stale for: " + text(stale, ", ") + "\n")
+    print("run 'make regen' or './cell --core . regen.cm' to update\n")
+  }
+}
+check_mach_stale()
+
 // analyze: tokenize + parse, check for errors
 function analyze(src, filename) {
   var tok_result = tokenize_mod(src, filename)