Add `pound-toggle` zle widget to work around the buggy built-in `pound-insert`

Refs #1533, #1534

modules/editor/init.zsh

@@ -241,6 +241,24 @@ function glob-alias {
 }
 zle -N glob-alias
 
+# Toggle the comment character at the start of the line. This is meant to work
+# around a buggy implementation of pound-insert in zsh.
+function pound-toggle {
+  if [[ "$BUFFER" = '#'* ]]; then
+    # Because of an oddity in how zsh handles the cursor when the buffer size
+    # changes, we need to make this check before we modify the buffer and let
+    # zsh handle moving the cursor back if it's past the end of the line.
+    if [[ $CURSOR != $#BUFFER ]]; then
+      (( CURSOR -= 1 ))
+    fi
+    BUFFER="${BUFFER:1}"
+  else
+    BUFFER="#$BUFFER"
+    (( CURSOR += 1 ))
+  fi
+}
+zle -N pound-toggle
+
 # Reset to default key bindings.
 bindkey -d
 
@@ -276,6 +294,10 @@ if (( $+widgets[history-incremental-pattern-search-backward] )); then
     history-incremental-pattern-search-forward
 fi
 
+# Toggle comment at the start of the line.
+bindkey -M emacs "$key_info[Escape];" pound-toggle
+
+
 #
 # Vi Key Bindings
 #