[demo/survey-loop] Repro of issue with mutating container in 'for'

This is issue #2243.

demo/survey-loop.sh

@@ -0,0 +1,99 @@
+#!/usr/bin/env bash
+#
+# Survey loop behavior
+#
+# Usage:
+#   demo/survey-str-api.sh <function name>
+
+set -o nounset
+set -o pipefail
+set -o errexit
+
+source build/dev-shell.sh  # python3 in $PATH
+
+# Python and JS string and regex replacement APIs
+
+mutate-py() {
+  echo ---
+  echo PY
+
+  python3 -c '
+mylist = [1,2,3]
+for x in mylist:
+  if x == 2:
+    mylist.append(99)
+  print(x)
+'
+}
+
+mutate-js() {
+  echo ---
+  echo 'JS let'
+
+  nodejs -e '
+let mylist = [1,2,3]
+for (let x of mylist) {
+  if (x === 2) {
+    mylist.push(99)
+  }
+  console.log(x)
+}
+'
+
+  echo ---
+  echo 'JS var'
+
+  nodejs -e '
+var mylist = [1,2,3]
+for (var x of mylist) {
+  if (x === 2) {
+    mylist.push(99)
+  }
+  console.log(x)
+}
+'
+}
+
+mutate-sh() {
+  local sh=${1:-bash}
+
+  echo ---
+  echo sh=$sh
+
+  $sh -c '
+  declare -a mylist=(1 2 3)
+  for x in "${mylist[@]}"; do
+    if test $x == 2; then
+      mylist+=(99)
+    fi
+    echo $x
+  done
+  echo "${mylist[@]}"
+'
+}
+
+mutate-ysh() {
+  echo ---
+  echo 'YSH'
+
+  ysh -c '
+var mylist = [1,2,3]
+for x in (mylist) {
+  if (x === 2) {
+    call mylist->append(99)
+  }
+  echo $x
+}
+'
+}
+
+compare-mutate() {
+  mutate-py
+  mutate-js
+  mutate-sh bash
+  mutate-sh osh
+  mutate-ysh
+}
+
+
+"$@"