refactor!: remove legacy parser feature and migrate to picker

The legacy `parser` feature and its module tree (`mingling::parser`,
`Argument`, `Picker`, `Pickable`, etc.) have been fully removed and
replaced by the `picker` feature powered by `arg-picker`.

BREAKING CHANGE: Remove `parser` feature and use `picker` instead.
Migration guide: Replace `features = ["parser"]` with
`features = ["picker"]` and update API usage per the provided table.

3 files changed, 50 insertions, 17 deletions

diff --git a/examples/example-enum-tag/Cargo.lock b/examples/example-enum-tag/Cargo.lock
index 868af79..492d708 100644
--- a/examples/example-enum-tag/Cargo.lock
+++ b/examples/example-enum-tag/Cargo.lock
@@ -3,6 +3,23 @@
 version = 4
 
 [[package]]
+name = "arg-picker"
+version = "0.2.0"
+dependencies = [
+ "arg-picker-macros",
+ "just_fmt 0.2.0",
+]
+
+[[package]]
+name = "arg-picker-macros"
+version = "0.2.0"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.118",
+]
+
+[[package]]
 name = "equivalent"
 version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -86,9 +103,9 @@ dependencies = [
 name = "mingling"
 version = "0.5.0"
 dependencies = [
+ "arg-picker",
  "mingling_core",
  "mingling_macros",
- "size",
 ]
 
 [[package]]
@@ -167,12 +184,6 @@ dependencies = [
 ]
 
 [[package]]
-name = "size"
-version = "0.5.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1b6709c7b6754dca1311b3c73e79fcce40dd414c782c66d88e8823030093b02b"
-
-[[package]]
 name = "syn"
 version = "2.0.118"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/examples/example-enum-tag/Cargo.toml b/examples/example-enum-tag/Cargo.toml
index 9c0a0ff..489f401 100644
--- a/examples/example-enum-tag/Cargo.toml
+++ b/examples/example-enum-tag/Cargo.toml
@@ -8,7 +8,7 @@ path = "../../mingling"
 
 features = [
     "comp",
-    "parser"
+    "picker"
 ]
 
 [workspace]
diff --git a/examples/example-enum-tag/src/main.rs b/examples/example-enum-tag/src/main.rs
index 2966036..c7fb502 100644
--- a/examples/example-enum-tag/src/main.rs
+++ b/examples/example-enum-tag/src/main.rs
@@ -16,8 +16,10 @@
 //! ```
 
 use mingling::{
-    macros::suggest_enum, parser::PickableEnum, prelude::*, EnumTag, Grouped, ShellContext,
-    Suggest,
+    EnumTag, Grouped, ShellContext, Suggest,
+    macros::suggest_enum,
+    picker::{PickerArgResult, SinglePickable},
+    prelude::*,
 };
 use std::io::Write;
 
@@ -57,9 +59,7 @@ pub enum ProgrammingLanguages {
     #[enum_desc("A general-purpose programming language with clean syntax, known for readability")]
     Python,
 
-    #[enum_desc(
-        "An object-oriented scripting language, famous for its concise and elegant syntax"
-    )]
+    #[enum_desc("An object-oriented scripting language, famous for its concise and elegant syntax")]
     Ruby,
 
     #[default]
@@ -68,9 +68,31 @@ pub enum ProgrammingLanguages {
 }
 
 // --------- IMPORTANT ---------
-// Implement the PickableEnum trait for ProgrammingLanguages,
-// so that `Picker` can parse this enum
-impl PickableEnum for ProgrammingLanguages {}
+// NOTE: Due to the migration from the legacy `parser` to `picker`, the `EnumTag` -> `Picker` path
+// is not yet complete, so a manual implementation is used for now.
+// Once that path is complete, `#[derive(EnumTag)]` can automatically implement `SinglePickable`,
+// replacing this manual implementation.
+impl SinglePickable for ProgrammingLanguages {
+    fn pick_single(str: Option<&str>) -> PickerArgResult<Self> {
+        let Some(str) = str else {
+            return PickerArgResult::NotFound;
+        };
+        let lang = match str.to_lowercase().as_str() {
+            "c" => Self::C,
+            "c++" | "cpp" => Self::CPlusPlus,
+            "c#" | "csharp" => Self::Csharp,
+            "java" => Self::Java,
+            "javascript" | "js" => Self::JavaScript,
+            "kotlin" => Self::Kotlin,
+            "ocaml" => Self::OCaml,
+            "python" => Self::Python,
+            "ruby" => Self::Ruby,
+            "rust" => Self::Rust,
+            _ => return PickerArgResult::NotFound,
+        };
+        PickerArgResult::Parsed(lang)
+    }
+}
 // --------- IMPORTANT ---------
 
 dispatcher!("lang-select", EntryLanguageSelection);
@@ -78,7 +100,7 @@ dispatcher!("lang-select", EntryLanguageSelection);
 #[chain]
 fn handle_language_selection(args: EntryLanguageSelection) -> Next {
     // You can use Picker to directly parse ProgrammingLanguages
-    let lang: ProgrammingLanguages = args.pick(()).unpack();
+    let lang: ProgrammingLanguages = args.pick_or_default(&arg![ProgrammingLanguages]).unwrap();
     lang.into()
 }