feat(picker): add core trait, types, and builder macro for argument

parsing

Implement the foundational `mingling_picker` library along with its
companion
`mingling_picker_macros` crate. The picker provides:

- `Pickable` trait for parsing types from raw strings
- `PickerResult` enum modeling parse outcomes
- `Picker` struct for storing and indexing command-line arguments
- `PickerRequirement` struct for declarative parameter definitions
- `PickerPattern` family (1..32) of typed pattern structs via the
  `internal_repeat` proc macro
- `req!` proc macro as a succinct builder for `PickerRequirement`

Re-export `mingling_picker::macros::*` from the `mingling` crate when
the
`picker` feature is enabled, replacing the previous wildcard re-export
of
`mingling_macros`.

1 files changed, 43 insertions, 0 deletions

diff --git a/mingling_picker/src/pickable/implements.rs b/mingling_picker/src/pickable/implements.rs
new file mode 100644
index 0000000..34f9727
--- /dev/null
+++ b/mingling_picker/src/pickable/implements.rs
@@ -0,0 +1,43 @@
+use crate::{Pickable, PickerResult};
+use std::path::PathBuf;
+
+macro_rules! impl_pickable {
+    ($($t:ty),*) => {
+        $(
+            impl Pickable for $t {
+                fn pick(raw_str: &str) -> PickerResult<Self> {
+                    raw_str.parse::<$t>().into()
+                }
+            }
+        )*
+    };
+}
+
+impl_pickable!(
+    i8, i16, i32, i64, i128, u8, u16, u32, u64, u128, usize, f32, f64, isize
+);
+
+impl Pickable for String {
+    fn pick(raw_str: &str) -> PickerResult<Self> {
+        PickerResult::Parsed(raw_str.to_string())
+    }
+}
+
+impl Pickable for PathBuf {
+    fn pick(raw_str: &str) -> PickerResult<Self> {
+        PickerResult::Parsed(PathBuf::from(raw_str))
+    }
+}
+
+impl<T: Pickable> Pickable for Option<T> {
+    fn pick(raw_str: &str) -> PickerResult<Self> {
+        if raw_str.is_empty() {
+            PickerResult::Parsed(None)
+        } else {
+            match T::pick(raw_str) {
+                PickerResult::Parsed(v) => PickerResult::Parsed(Some(v)),
+                _ => PickerResult::Parsed(None),
+            }
+        }
+    }
+}