refactor: Harden against occur/val ordering

This makes some naming more explicit and allows us to increment
occurrences before adding values (which is the logical mental order and
allows other improvements).

src/parse/arg_matcher.rs

@@ -176,8 +176,11 @@ impl ArgMatcher {
         ma.push_index(idx);
     }
 
-    pub(crate) fn arg_have_val(&mut self, arg: &Id) -> bool {
-        matches!(self.entry(arg), Entry::Occupied(_))
+    pub(crate) fn has_val_groups(&mut self, arg: &Id) -> bool {
+        match self.entry(arg) {
+            Entry::Occupied(e) => e.get().has_val_groups(),
+            Entry::Vacant(_) => false,
+        }
     }
 
     pub(crate) fn needs_more_vals(&self, o: &Arg) -> bool {

src/parse/matches/matched_arg.rs

@@ -81,6 +81,10 @@ impl MatchedArg {
         self.vals.iter().flatten().count() == 0
     }
 
+    pub(crate) fn has_val_groups(&self) -> bool {
+        !self.vals.is_empty()
+    }
+
     // Will be used later
     #[allow(dead_code)]
     pub(crate) fn remove_vals(&mut self, len: usize) {

src/parse/parser.rs

@@ -594,7 +594,7 @@ impl<'help, 'app> Parser<'help, 'app> {
                 // Creating new value group rather than appending when the arg
                 // doesn't have any value. This behaviour is right because
                 // positional arguments are always present continuously.
-                let append = self.arg_have_val(matcher, p);
+                let append = self.has_val_groups(matcher, p);
                 self.add_val_to_arg(
                     p,
                     &arg_os,
@@ -1463,8 +1463,8 @@ impl<'help, 'app> Parser<'help, 'app> {
         matcher.add_index_to(&arg.id, self.cur_idx.get(), ty);
     }
 
-    fn arg_have_val(&self, matcher: &mut ArgMatcher, arg: &Arg<'help>) -> bool {
-        matcher.arg_have_val(&arg.id)
+    fn has_val_groups(&self, matcher: &mut ArgMatcher, arg: &Arg<'help>) -> bool {
+        matcher.has_val_groups(&arg.id)
     }
 
     fn parse_flag(&self, flag: &Arg<'help>, matcher: &mut ArgMatcher) -> ParseResult {