[demo] Repro of bug #858.

I guess this is about when the main loop runs signal handlers.

Unrelated: doc edits.

Author: Andy Chu

demo/bug-858-trap.sh

@@ -0,0 +1,12 @@
+action() {
+  echo "from signal"
+}
+
+trap "action" USR1
+
+echo "Run: kill -USR1 $$; date"
+while true; do
+  date
+	sleep 10 &
+	wait $!
+done

doc/variable-scope.md

@@ -18,6 +18,10 @@ Also see [Oil Keywords](oil-keywords.html).
 
 This doc is filled with details, so it will help to keep these goals in mind:
 
+- Code written in Oil style (with `proc`) is easier to read/audit than code
+  written in shell style.
+  - in shell, functions can pollute the caller's stack, because of the dynamic
+    scope rule.
 - Remove dynamic scope.  This mechanism is unfamiliar to most programmers, and
   may result in mutating variables where you don't expect it.
   - Instead of using dynamic scope by default, Oil lets you choose it
@@ -59,7 +63,12 @@ Don't use the old style of `local`, `readonly`, `x=y`.
 
 This covers 95%+ of shell programming.
 
-### `shopt --unset dynamic_scope`  in `bin/oil`
+### When Dynamic Scope Is Off
+
+`shopt --unset dynamic_scope` 
+
+- it's off when calling a `proc`.
+- it's off in  `bin/oil`
 
 This option affects how nearly **every** shell assignment construct behaves.  There are a lot of them!
 
@@ -136,8 +145,11 @@ The other ones deal with values.  These deal with cells.  These also change to
   - `declare -p` to print variables
   - `${x@a}` to print flags
   - `pp .cell`
+
   - weird `TZ` test in `printf`.  I think this could just look in the
     environment itself?  Do `getenv()`?
+    - yeah I think this is a separate case
+    - I think it should just look for a GLOBAL honestly
 
 
 ### `Dynamic` → `LocalOnly` (keyword `setlocal`)

mycpp/cppgen_pass.py

@@ -1909,7 +1909,7 @@ def visit_func_def(self, o: 'mypy.nodes.FuncDef') -> T:
             # osh/word_eval.py
             class_name is None and func_name == 'CheckCompatArray' or
             # core/state.py
-            class_name is None and func_name in ('_PackFlags', 'SetVar') or
+            class_name is None and func_name in ('_PackFlags', 'SetLocalShopt') or
             class_name == 'Mem' and func_name in ('GetValue', 'SetValue', 'GetCell') or
             class_name == 'SearchPath' and func_name == 'Lookup' or
             # core/ui.py