Parser logic clean up

src/build/app/settings.rs

@@ -1046,12 +1046,16 @@ pub enum AppSettings {
     TrailingValues,
 
     #[doc(hidden)]
+    /// If the app is already built, used for caching.
     Built,
 
     #[doc(hidden)]
+    /// If the app's bin name is already built, used for caching.
     BinNameBuilt,
 
     #[doc(hidden)]
+    /// This is paired with `ArgsNegateSubcommands`. Used to determine if we
+    /// already met any valid arg(then we shouldn't expect subcommands after it).
     ValidArgFound,
 
     #[doc(hidden)]

src/output/usage.rs

@@ -365,6 +365,8 @@ impl<'help, 'app, 'parser> Usage<'help, 'app, 'parser> {
     // `incl_last`: should we include args that are Arg::Last? (i.e. `prog [foo] -- [last]). We
     // can't do that for required usages being built for subcommands because it would look like:
     // `prog [foo] -- [last] <subcommand>` which is totally wrong.
+    // TODO: remove the allow clippy when we update the compiler version.
+    #[allow(clippy::needless_collect)]
     pub(crate) fn get_required_usage_from(
         &self,
         incls: &[Id],
@@ -419,7 +421,7 @@ impl<'help, 'app, 'parser> Usage<'help, 'app, 'parser> {
 
         for p in pmap.values() {
             debug!("Usage::get_required_usage_from:iter:{:?}", p.id);
-            if args_in_groups.is_empty() || !args_in_groups.contains(&p.id) {
+            if !args_in_groups.contains(&p.id) {
                 ret_val.push(p.to_string());
             }
         }

src/parse/arg_matcher.rs

@@ -130,7 +130,10 @@ impl ArgMatcher {
 
     pub(crate) fn add_val_to(&mut self, arg: &Id, val: OsString, ty: ValueType) {
         let ma = self.entry(arg).or_insert(MatchedArg {
-            occurs: 0, // @TODO @question Shouldn't this be 1 if we're already adding a value to this arg?
+            // We will manually inc occurrences later(for flexibility under
+            // specific circumstances, like only add one occurrence for flag
+            // when we met: `--flag=one,two`).
+            occurs: 0,
             ty,
             indices: Vec::with_capacity(1),
             vals: Vec::with_capacity(1),