Add a test file to check the hack that errortrace uses.

(Makes it easy to know when it breaks, and hopefully to fix it when that
happens)

collects/meta/props

@@ -1409,6 +1409,7 @@ path/s is either such a string or a list of them.
 "collects/tests/drracket/teaching-lang-save-file.rkt" drdr:command-line (gracket *)
 "collects/tests/drracket/teachpack.rkt" drdr:command-line (gracket *)
 "collects/tests/drracket/time-keystrokes.rkt" drdr:command-line (gracket-text "-t" *)
+"collects/tests/errortrace/alert.rkt" responsible (eli)
 "collects/tests/framework" responsible (robby)
 "collects/tests/framework/canvas.rkt" drdr:command-line (mzc "-k" *)
 "collects/tests/framework/debug.rkt" drdr:command-line (mzc "-k" *)

collects/tests/errortrace/alert.rkt

@@ -0,0 +1,22 @@
+#lang racket/base
+
+(require tests/eli-tester (for-syntax racket/base))
+
+;; All current uses of the errortrace collection (there are currently 4:
+;; in the sandbox, drracket, and in htdp and deinprogramm) rely on
+;; making "self-modifying" code by using a single mpair in source code.
+;; This is a fragile hole, and it might be plugged at some point in the
+;; future.  (Another alternative is to inject a closure as a value into
+;; the syntax, which is similarly hackish.)  The purpose of this test is
+;; to fail when that happens, so we remember to deal with it in these
+;; uses.  A convenient commit to refer to is 2189957 -- it touches all
+;; four places.  (BTW, note that this file cannot be compiled because of
+;; this.)
+
+(define-syntax m
+  (let ([b (mcons 0 0)])
+    (lambda (stx)
+      (with-syntax ([b b])
+        #'(lambda () (set-mcar! b (add1 (mcar b))) (mcar b))))))
+(let ([f m])
+  (test (list (f) (f) (f)) => '(1 2 3)))

collects/tests/info.rkt

@@ -8,6 +8,7 @@
   '("2htdp"
     "aligned-pasteboard"
     "deinprogramm"
+    "errortrace"
     "future"
     "gracket"
     "honu"
@@ -19,7 +20,6 @@
     "plai"
     "planet"
     "plot"
-    "profj"
     "r6rs"
     "rackunit"
     "srfi"

collects/tests/run-automated-tests.rkt

@@ -41,6 +41,7 @@
   (test "net/main.rkt")
   (test "file/main.rkt")
   (test "profile/main.rkt")
+  (test "errortrace/alert.rkt")
   )
 
 (require racket/runtime-path)