fix(parser): Fill in defaults on ignored error

This came up in #5812 and is especially problematic for derives.

Not really a fan of this solution but its the least invasive.
I also considered going wild with error recovery or moving towards a
solution for #1546.

Author: epage

clap_builder/src/parser/parser.rs

@@ -54,7 +54,14 @@ impl<'cmd> Parser<'cmd> {
     ) -> ClapResult<()> {
         debug!("Parser::get_matches_with");
 
-        ok!(self.parse(matcher, raw_args, args_cursor));
+        ok!(self.parse(matcher, raw_args, args_cursor).map_err(|err| {
+            if self.cmd.is_ignore_errors_set() {
+                #[cfg(feature = "env")]
+                let _ = self.add_env(matcher);
+                let _ = self.add_defaults(matcher);
+            }
+            err
+        }));
         ok!(self.resolve_pending(matcher));
 
         #[cfg(feature = "env")]

tests/builder/ignore_errors.rs

@@ -113,7 +113,7 @@ fn unexpected_argument() {
         m.get_one::<String>("config").cloned(),
         Some("config file".to_owned())
     );
-    assert_eq!(m.get_one::<bool>("unset-flag").copied(), None);
+    assert_eq!(m.get_one::<bool>("unset-flag").copied(), Some(false));
 }
 
 #[test]