docs(tutorial): Split into separate modules per section

Unsure how much to read into this but some refer to the tutorial a a big
wall of ... and maybe breaking it down will help?

src/_derive/_tutorial/chapter_0.rs

@@ -0,0 +1,25 @@
+//! ## Quick Start
+//!
+//! You can create an application declaratively with a `struct` and some
+//! attributes.
+//!
+//! First, ensure `clap` is available with the [`derive` feature flag][crate::_features]:
+//! ```console
+//! $ cargo add clap --features derive
+//! ```
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/01_quick.rs")]
+//! ```
+//!
+#![doc = include_str!("../../../examples/tutorial_derive/01_quick.md")]
+//!
+//! See also
+//! - [FAQ: When should I use the builder vs derive APIs?][crate::_faq#when-should-i-use-the-builder-vs-derive-apis]
+//! - The [cookbook][crate::_cookbook] for more application-focused examples
+
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_1 as next;
+pub use crate::_tutorial as table_of_contents;

src/_derive/_tutorial/chapter_1.rs

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+//! ## Configuring the Parser
+//!
+//! You use derive [`Parser`][crate::Parser] to start building a parser.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/02_apps.rs")]
+//! ```
+//!
+#![doc = include_str!("../../../examples/tutorial_derive/02_apps.md")]
+//!
+//! You can use [`#[command(author, version, about)]` attribute defaults][super#command-attributes] on the struct to fill these fields in from your `Cargo.toml` file.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/02_crate.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/02_crate.md")]
+//!
+//! You can use `#[command]` attributes on the struct to change the application level behavior of clap.  Any [`Command`][crate::Command] builder function can be used as an attribute, like [`Command::next_line_help`].
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/02_app_settings.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/02_app_settings.md")]
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_0 as previous;
+pub use super::chapter_2 as next;
+pub use crate::_tutorial as table_of_contents;

src/_derive/_tutorial/chapter_2.rs

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+//! ## Adding Arguments
+//!
+//! 1. [Positionals](#positionals)
+//! 2. [Options](#options)
+//! 3. [Flags](#flags)
+//! 4. [Subcommands](#subcommands)
+//! 5. [Defaults](#defaults)
+//!
+//! Arguments are inferred from the fields of your struct.
+//!
+//! ### Positionals
+//!
+//! You can have users specify values by their position on the command-line:
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_03_positional.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_03_positional.md")]
+//!
+//! Note that the [default `ArgAction` is `Set`][super#arg-types].  To
+//! accept multiple values, override the [action][Arg::action] with [`Append`][crate::ArgAction::Append] via `Vec`:
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_03_positional_mult.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_03_positional_mult.md")]
+//!
+//! ### Options
+//!
+//! You can name your arguments with a flag:
+//! - Order doesn't matter
+//! - They can be optional
+//! - Intent is clearer
+//!
+//! To specify the flags for an argument, you can use [`#[arg(short = 'n')]`][Arg::short] and/or
+//! [`#[arg(long = "name")]`][Arg::long] attributes on a field.  When no value is given (e.g.
+//! `#[arg(short)]`), the flag is inferred from the field's name.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_02_option.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_02_option.md")]
+//!
+//! Note that the [default `ArgAction` is `Set`][super#arg-types].  To
+//! accept multiple occurrences, override the [action][Arg::action] with [`Append`][crate::ArgAction::Append] via `Vec`:
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_02_option_mult.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_02_option_mult.md")]
+//!
+//! ### Flags
+//!
+//! Flags can also be switches that can be on/off:
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_01_flag_bool.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_01_flag_bool.md")]
+//!
+//! Note that the [default `ArgAction` for a `bool` field is
+//! `SetTrue`][super#arg-types].  To accept multiple flags, override the [action][Arg::action] with
+//! [`Count`][crate::ArgAction::Count]:
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_01_flag_count.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_01_flag_count.md")]
+//!
+//! This also shows that any[`Arg`][crate::Args] method may be used as an attribute.
+//!
+//! ### Subcommands
+//!
+//! Subcommands are derived with `#[derive(Subcommand)]` and be added via
+//! [`#[command(subcommand)]` attribute][super#command-attributes] on the field using that type.
+//! Each instance of a [Subcommand][crate::Subcommand] can have its own version, author(s), Args,
+//! and even its own subcommands.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_04_subcommands.rs")]
+//! ```
+//! We used a struct-variant to define the `add` subcommand.
+//! Alternatively, you can use a struct for your subcommand's arguments:
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_04_subcommands_alt.rs")]
+//! ```
+//!
+#![doc = include_str!("../../../examples/tutorial_derive/03_04_subcommands.md")]
+//!
+//! ### Defaults
+//!
+//! We've previously showed that arguments can be [`required`][crate::Arg::required] or optional.
+//! When optional, you work with a `Option` and can `unwrap_or`.  Alternatively, you can
+//! set [`#[arg(default_value_t)]`][super#arg-attributes].
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/03_05_default_values.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/03_05_default_values.md")]
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_1 as previous;
+pub use super::chapter_3 as next;
+pub use crate::_tutorial as table_of_contents;

src/_derive/_tutorial/chapter_3.rs

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+//! ## Validation
+//!
+//! 1. [Enumerated values](#enumerated-values)
+//! 2. [Validated values](#validated-values)
+//! 3. [Argument Relations](#argument-relations)
+//! 4. [Custom Validation](#custom-validation)
+//!
+//! An appropriate default parser/validator will be selected for the field's type.  See
+//! [`value_parser!`][crate::value_parser!] for more details.
+//!
+//! ### Enumerated values
+//!
+//! For example, if you have arguments of specific values you want to test for, you can derive
+//! [`ValueEnum`][super#valueenum-attributes]
+//! (any [`PossibleValue`] builder function can be used as a `#[value]` attribute on enum variants).
+//!
+//! This allows you specify the valid values for that argument. If the user does not use one of
+//! those specific values, they will receive a graceful exit with error message informing them
+//! of the mistake, and what the possible valid values are
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/04_01_enum.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/04_01_enum.md")]
+//!
+//! ### Validated values
+//!
+//! More generally, you can validate and parse into any data type with [`Arg::value_parser`].
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/04_02_parse.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/04_02_parse.md")]
+//!
+//! A [custom parser][TypedValueParser] can be used to improve the error messages or provide additional validation:
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/04_02_validate.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/04_02_validate.md")]
+//!
+//! See [`Arg::value_parser`][crate::Arg::value_parser] for more details.
+//!
+//! ### Argument Relations
+//!
+//! You can declare dependencies or conflicts between [`Arg`][crate::Arg]s or even
+//! [`ArgGroup`][crate::ArgGroup]s.
+//!
+//! [`ArgGroup`][crate::ArgGroup]s  make it easier to declare relations instead of having to list
+//! each individually, or when you want a rule to apply "any but not all" arguments.
+//!
+//! Perhaps the most common use of [`ArgGroup`][crate::ArgGroup]s is to require one and *only* one
+//! argument to be present out of a given set. Imagine that you had multiple arguments, and you
+//! want one of them to be required, but making all of them required isn't feasible because perhaps
+//! they conflict with each other.
+//!
+//! [`ArgGroup`][crate::ArgGroup]s are automatically created for a `struct` with its
+//! [`ArgGroup::id`][crate::ArgGroup::id] being the struct's name.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/04_03_relations.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/04_03_relations.md")]
+//!
+//! ### Custom Validation
+//!
+//! As a last resort, you can create custom errors with the basics of clap's formatting.
+//!
+//! ```rust
+#![doc = include_str!("../../../examples/tutorial_derive/04_04_custom.rs")]
+//! ```
+#![doc = include_str!("../../../examples/tutorial_derive/04_04_custom.md")]
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_2 as previous;
+pub use super::chapter_4 as next;
+pub use crate::_tutorial as table_of_contents;

src/_derive/_tutorial/chapter_4.rs

@@ -0,0 +1,15 @@
+//! ## Testing
+//!
+//! clap reports most development errors as `debug_assert!`s.  Rather than checking every
+//! subcommand, you should have a test that calls
+//! [`Command::debug_assert`][crate::Command::debug_assert]:
+//! ```rust,no_run
+#![doc = include_str!("../../../examples/tutorial_derive/05_01_assert.rs")]
+//! ```
+
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_3 as previous;
+pub use super::chapter_5 as next;
+pub use crate::_tutorial as table_of_contents;

src/_derive/_tutorial/chapter_5.rs

@@ -0,0 +1,14 @@
+//! ## Next Steps
+//!
+//! - [Cookbook][crate::_cookbook] for application-focused examples
+//! - Explore more features in the [Derive reference][super]
+//!   - See also [`Command`], [`Arg`], [`ArgGroup`], and [`PossibleValue`] builder functions which
+//!     can be used as attributes
+//!
+//! For support, see [Discussions](https://github.com/clap-rs/clap/discussions)
+
+#![allow(unused_imports)]
+use crate::builder::*;
+
+pub use super::chapter_4 as previous;
+pub use crate::_tutorial as table_of_contents;