Brute force attempt at clap-rs#1596

 * This escapes everything that comes up in the reproducer from the
   above issue. NB: this means possible_value only.

missing:

 * possible_value(...).about
 * Arg(...).value_name[s]
 * Arg(...).about
 * Arg(...).long

clap_generate/src/generators/shells/zsh.rs

@@ -358,7 +358,7 @@ fn value_completion(arg: &Arg) -> Option<String> {
                         } else {
                             Some(format!(
                                 r#"{name}\:"{about}""#,
-                                name = escape_value(value.get_name()),
+                                name = escape_value(value.get_name(), true),
                                 about = value.get_about().map(escape_help).unwrap_or_default()
                             ))
                         }
@@ -371,7 +371,15 @@ fn value_completion(arg: &Arg) -> Option<String> {
                 "({})",
                 values
                     .iter()
-                    .filter_map(ArgValue::get_visible_name)
+                    // .filter_map(ArgValue::get_visible_name)
+                    .filter_map(|value| {
+                        if value.is_hidden() {
+                            None
+                        } else {
+                            Some(format!("{}", escape_value(value.get_name(), false)
+                            ))
+                        }
+                    })
                     .collect::<Vec<_>>()
                     .join(" ")
             ))
@@ -411,13 +419,34 @@ fn escape_help(string: &str) -> String {
 }
 
 /// Escape value string inside single quotes and parentheses
-fn escape_value(string: &str) -> String {
+fn escape_value(string: &str, for_about: bool) -> String {
     string
-        .replace("\\", "\\\\")
-        .replace("'", "'\\''")
+        // .replace("\\", "\\\\")
+        // .replace("\\", "\\\\\\\\")   // ':: :((\\\\\:"some descr"))' \
+        .replace("\\", if for_about {"\\\\\\\\"} else {"\\\\"})
+        .replace("'", "'\\\\\\''")
         .replace("(", "\\(")
         .replace(")", "\\)")
+        .replace("[", "\\[")
+        .replace("]", "\\]")
         .replace(" ", "\\ ")
+        .replace("$", "\\$")
+        .replace("`", "\\`")
+        .replace("\"", "\\\"")
+        .replace("&", "\\&")
+        .replace("#", "\\#")
+        .replace("{", "\\{")
+        .replace("|", "\\|")
+        .replace("}", "\\}")
+        .replace("~", "\\~")
+        .replace("?", "\\?")
+        .replace("^", "\\^")
+        .replace("*", "\\*")
+        .replace(";", "\\;")
+        .replace("<", "\\<")
+        .replace(">", "\\>")
+        .replace("=", "\\=")   // ':: :((\=\:"some descr"))' \
+        .replace(":", if for_about {"\\\\\\:"} else {":"})   // ':: :((\\\:\:"some descr"))' \
 }
 
 fn write_opts_of(p: &App, p_global: Option<&App>) -> String {