mode selection process outlined in 'arg::parsing::into_mode'

src/arg/parsing.rs

@@ -32,10 +32,43 @@ pub enum Argument
     Input(String),
 }
 
+/// Kinds of modes of operation for the program.
+///
+/// These map to `super::Mode`.
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd, Copy)]
+#[non_exhaustive]
+enum ModeKind
+{
+    Normal,
+    
+    Help
+}
+
+impl Default for ModeKind
+{
+    #[inline]
+    fn default() -> Self
+    {
+	Self::Normal
+    }
+}
+
+
 impl Argument
 {
+    /// What mode does this argument change to, if any?
+    fn mode_change_kind(&self) -> Option<ModeKind>
+    {
+	Some(match self
+	     {
+		 Self::ModeChangeHelp => ModeKind::Help,
+		 _ => return None,
+	     })
+    }
     /// Convert into a mode change if this is a mode change
     // We consume the whole output here in case the mode change needs to traverse it for information. As of now, we have only one non-`Normal` mode: `Help`, which doesn't require any extra information.
+
+    #[deprecated(note = "mode selection happens in `into_mode` and early return through `Continue::Abort` will be removed or reworked to not require this function.")]
     pub fn try_into_mode(self, _rest: Output) -> Result<Mode, (Self, Output)>
     {
 	match self {
@@ -233,6 +266,8 @@ pub enum Continue
     ///
     /// Returning this when the contained value is `Some` immediately terminates parsing and precedes to mode-switch. However, if it is `None`, parsing of chained short args is allowed to continue, although `Abort(None)` will be returned at the end regardless of subsequent `Continue` results from that change (unless one is an `Abort(Some(_))`, which immediately returns itself.)
     // Box `Argument` to reduce the size of `Continue`, as it is returned from functions often and when its value is set to `Some` it will always be the last `Argument` processed anyway and the only one to be boxed here at all.
+
+    //TODO: Deprecate the early return of an `Argument` here. Either change it to `Mode`, or have no early return. Mode change happens at the bottom in `into_mode` now.
     Abort(Option<Box<Argument>>),
 }
 
@@ -416,9 +451,21 @@ mod modes {
 /// Consume this parsed list of arguments into a `Mode` and return it
 pub fn into_mode(args: Output) -> eyre::Result<Mode>
 {
-    //TODO: Find out what mode `args` is in.
-    
-    //TODO: pass `args` to the respective mode generation function in mode `modes`, and wrap that mode around its return value.
+    let mut mode_kind = ModeKind::default(); //Normal.
+
+    for arg in args.iter() {
+	//find any mode change Argument (with `Argument::mode_change_kind()`) in `args`, changing `mode_kind` in turn. There should be at most 1.
+	if let Some(mode) = arg.mode_change_kind()
+	{
+	    mode_kind = mode;
+	    break;
+	}
+    }
+    //pass `args` to the respective mode generation function in mode `modes`, and wrap that mode around its return value.
+    match mode_kind
+    {
+	ModeKind::Normal => modes::normal(args).map(Mode::Normal),
+	ModeKind::Help => Ok(Mode::Help),
+    }
     
-    todo!()
 }