src/_derive/mod.rs

//! # Documentation: Derive Reference
//!
//! 1. [Overview](#overview)
//! 2. [Attributes](#attributes)
//!     1. [Terminology](#terminology)
//!     2. [Command Attributes](#command-attributes)
//!     2. [ArgGroup Attributes](#arggroup-attributes)
//!     3. [Arg Attributes](#arg-attributes)
//!     4. [ValueEnum Attributes](#valueenum-attributes)
//!     5. [Possible Value Attributes](#possible-value-attributes)
//! 3. [Arg Types](#arg-types)
//! 4. [Doc Comments](#doc-comments)
//! 5. [Mixing Builder and Derive APIs](#mixing-builder-and-derive-apis)
//! 6. [Tips](#tips)
//!
//! ## Overview
//!
//! To derive `clap` types, you need to enable the [`derive` feature flag][crate::_features].
//!
//! Example:
//! ```rust
#![doc = include_str!("../../examples/demo.rs")]
//! ```
//!
//! Let's start by breaking down the anatomy of the derive attributes:
//! ```rust
//! use clap::{Parser, Args, Subcommand, ValueEnum};
//!
//! /// Doc comment
//! #[derive(Parser)]
//! #[command(CMD ATTRIBUTE)]
//! #[group(GROUP ATTRIBUTE)]
//! struct Cli {
//!     /// Doc comment
//!     #[arg(ARG ATTRIBUTE)]
//!     field: UserType,
//!
//!     #[arg(value_enum, ARG ATTRIBUTE...)]
//!     field: EnumValues,
//!
//!     #[command(flatten)]
//!     delegate: Struct,
//!
//!     #[command(subcommand)]
//!     command: Command,
//! }
//!
//! /// Doc comment
//! #[derive(Args)]
//! #[command(PARENT CMD ATTRIBUTE)]
//! #[group(GROUP ATTRIBUTE)]
//! struct Struct {
//!     /// Doc comment
//!     #[command(ARG ATTRIBUTE)]
//!     field: UserType,
//! }
//!
//! /// Doc comment
//! #[derive(Subcommand)]
//! #[command(PARENT CMD ATTRIBUTE)]
//! enum Command {
//!     /// Doc comment
//!     #[command(CMD ATTRIBUTE)]
//!     Variant1(Struct),
//!
//!     /// Doc comment
//!     #[command(CMD ATTRIBUTE)]
//!     Variant2 {
//!         /// Doc comment
//!         #[arg(ARG ATTRIBUTE)]
//!         field: UserType,
//!     }
//! }
//!
//! /// Doc comment
//! #[derive(ValueEnum)]
//! #[value(VALUE ENUM ATTRIBUTE)]
//! enum EnumValues {
//!     /// Doc comment
//!     #[value(POSSIBLE VALUE ATTRIBUTE)]
//!     Variant1,
//! }
//!
//! fn main() {
//!     let cli = Cli::parse();
//! }
//! ```
//!
//! Traits:
//! - [`Parser`][crate::Parser] parses arguments into a `struct` (arguments) or `enum` (subcommands).
//!   - [`Args`][crate::Args] allows defining a set of re-usable arguments that get merged into their parent container.
//!   - [`Subcommand`][crate::Subcommand] defines available subcommands.
//!   - Subcommand arguments can be defined in a struct-variant or automatically flattened with a tuple-variant.
//! - [`ValueEnum`][crate::ValueEnum] allows parsing a value directly into an `enum`, erroring on unsupported values.
//!   - The derive doesn't work on enums that contain non-unit variants, unless they are skipped
//!
//! *See also the [derive tutorial][crate::_derive::_tutorial] and [cookbook][crate::_cookbook]*
//!
//! ## Attributes
//!
//! ### Terminology
//!
//! **Raw attributes** are forwarded directly to the underlying [`clap` builder][crate::builder].  Any
//! [`Command`][crate::Command], [`Arg`][crate::Arg], or [`PossibleValue`][crate::builder::PossibleValue] method can be used as an attribute.
//!
//! Raw attributes come in two different syntaxes:
//! ```rust,ignore
//! #[arg(
//!     global = true, // name = arg form, neat for one-arg methods
//!     required_if_eq("out", "file") // name(arg1, arg2, ...) form.
//! )]
//! ```
//!
//! - `method = arg` can only be used for methods which take only one argument.
//! - `method(arg1, arg2)` can be used with any method.
//!
//! As long as `method_name` is not one of the magical methods it will be
//! translated into a mere method call.
//!
//! **Magic attributes** have post-processing done to them, whether that is
//! - Providing of defaults
//! - Special behavior is triggered off of it
//!
//! Magic attributes are more constrained in the syntax they support, usually just
//! `<attr> = <value>` though some use `<attr>(<value>)` instead.  See the specific
//! magic attributes documentation for details.  This allows users to access the
//! raw behavior of an attribute via `<attr>(<value>)` syntax.
//!
//! **NOTE:** Some attributes are inferred from [Arg Types](#arg-types) and [Doc
//! Comments](#doc-comments).  Explicit attributes take precedence over inferred
//! attributes.
//!
//! ### Command Attributes
//!
//! These correspond to a [`Command`][crate::Command] which is used for both top-level parsers and
//! when defining subcommands.
//!
//! **Raw attributes:**  Any [`Command` method][crate::Command] can also be used as an attribute,
//! see [Terminology](#terminology) for syntax.
//! - e.g. `#[command(arg_required_else_help(true))]` would translate to `cmd.arg_required_else_help(true)`
//!
//! **Magic attributes:**
//! - `name  = <expr>`: [`Command::name`][crate::Command::name]
//!   - When not present: [crate `name`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-name-field) (if on [`Parser`][crate::Parser] container), variant name (if on [`Subcommand`][crate::Subcommand] variant)
//! - `version [= <expr>]`: [`Command::version`][crate::Command::version]
//!   - When not present: no version set
//!   - Without `<expr>`: defaults to [crate `version`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-version-field)
//! - `author [= <expr>]`: [`Command::author`][crate::Command::author]
//!   - When not present: no author set
//!   - Without `<expr>`: defaults to [crate `authors`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-authors-field)
//! - `about [= <expr>]`: [`Command::about`][crate::Command::about]
//!   - When not present: [Doc comment summary](#doc-comments)
//!   - Without `<expr>`: [crate `description`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-description-field) ([`Parser`][crate::Parser] container)
//!     - **TIP:** When a doc comment is also present, you most likely want to add
//!       `#[arg(long_about = None)]` to clear the doc comment so only [`about`][crate::Command::about]
//!       gets shown with both `-h` and `--help`.
//! - `long_about[ = <expr>]`: [`Command::long_about`][crate::Command::long_about]
//!   - When not present: [Doc comment](#doc-comments) if there is a blank line, else nothing
//!   - When present without a value: [Doc comment](#doc-comments)
//! - `verbatim_doc_comment`: Minimizes pre-processing when converting doc comments to [`about`][crate::Command::about] / [`long_about`][crate::Command::long_about]
//! - `next_display_order`: [`Command::next_display_order`][crate::Command::next_display_order]
//! - `next_help_heading`: [`Command::next_help_heading`][crate::Command::next_help_heading]
//!   - When `flatten`ing [`Args`][crate::Args], this is scoped to just the args in this struct and any struct `flatten`ed into it
//! - `rename_all = <string_literal>`: Override default field / variant name case conversion for [`Command::name`][crate::Command::name] / [`Arg::id`][crate::Arg::id]
//!   - When not present: `"kebab-case"`
//!   - Available values: `"camelCase"`, `"kebab-case"`, `"PascalCase"`, `"SCREAMING_SNAKE_CASE"`, `"snake_case"`, `"lower"`, `"UPPER"`, `"verbatim"`
//! - `rename_all_env = <string_literal>`: Override default field name case conversion for env variables for  [`Arg::env`][crate::Arg::env]
//!   - When not present: `"SCREAMING_SNAKE_CASE"`
//!   - Available values: `"camelCase"`, `"kebab-case"`, `"PascalCase"`, `"SCREAMING_SNAKE_CASE"`, `"snake_case"`, `"lower"`, `"UPPER"`, `"verbatim"`
//!
//! And for [`Subcommand`][crate::Subcommand] variants:
//! - `skip`: Ignore this variant
//! - `flatten`: Delegates to the variant for more subcommands (must implement
//!   [`Subcommand`][crate::Subcommand])
//! - `subcommand`: Nest subcommands under the current set of subcommands (must implement
//!   [`Subcommand`][crate::Subcommand])
//! - `external_subcommand`: [`Command::allow_external_subcommand(true)`][crate::Command::allow_external_subcommands]
//!   - Variant must be either `Variant(Vec<String>)` or `Variant(Vec<OsString>)`
//!
//! And for [`Args`][crate::Args] fields:
//! - `flatten`: Delegates to the field for more arguments (must implement [`Args`][crate::Args])
//!   - Only [`next_help_heading`][crate::Command::next_help_heading] can be used with `flatten`.  See
//!     [clap-rs/clap#3269](https://github.com/clap-rs/clap/issues/3269) for why
//!     arg attributes are not generally supported.
//!   - **Tip:** Though we do apply a flattened [`Args`][crate::Args]'s Parent Command Attributes, this
//!     makes reuse harder. Generally prefer putting the cmd attributes on the
//!     [`Parser`][crate::Parser] or on the flattened field.
//! - `subcommand`: Delegates definition of subcommands to the field (must implement
//!   [`Subcommand`][crate::Subcommand])
//!   - When `Option<T>`, the subcommand becomes optional
//!
//! ### ArgGroup Attributes
//!
//! These correspond to the [`ArgGroup`][crate::ArgGroup] which is implicitly created for each
//! `Args` derive.
//!
//! At the moment, only `#[group(skip)]` is supported
//!
//! ### Arg Attributes
//!
//! These correspond to a [`Arg`][crate::Arg].
//!
//! **Raw attributes:**  Any [`Arg` method][crate::Arg] can also be used as an attribute, see [Terminology](#terminology) for syntax.
//! - e.g. `#[arg(max_values(3))]` would translate to `arg.max_values(3)`
//!
//! **Magic attributes**:
//! - `id = <expr>`: [`Arg::id`][crate::Arg::id]
//!   - When not present: case-converted field name is used
//! - `value_parser [= <expr>]`: [`Arg::value_parser`][crate::Arg::value_parser]
//!   - When not present: will auto-select an implementation based on the field type using
//!     [`value_parser!`][crate::value_parser!]
//! - `action [= <expr>]`: [`Arg::action`][crate::Arg::action]
//!   - When not present: will auto-select an action based on the field type
//! - `help = <expr>`: [`Arg::help`][crate::Arg::help]
//!   - When not present: [Doc comment summary](#doc-comments)
//! - `long_help[ = <expr>]`: [`Arg::long_help`][crate::Arg::long_help]
//!   - When not present: [Doc comment](#doc-comments) if there is a blank line, else nothing
//!   - When present without a value: [Doc comment](#doc-comments)
//! - `verbatim_doc_comment`: Minimizes pre-processing when converting doc comments to [`help`][crate::Arg::help] / [`long_help`][crate::Arg::long_help]
//! - `short [= <char>]`: [`Arg::short`][crate::Arg::short]
//!   - When not present: no short set
//!   - Without `<char>`: defaults to first character in the case-converted field name
//! - `long [= <str>]`: [`Arg::long`][crate::Arg::long]
//!   - When not present: no long set
//!   - Without `<str>`: defaults to the case-converted field name
//! - `env [= <str>]`: [`Arg::env`][crate::Arg::env] (needs [`env` feature][crate::_features] enabled)
//!   - When not present: no env set
//!   - Without `<str>`: defaults to the case-converted field name
//! - `from_global`: Read a [`Arg::global`][crate::Arg::global] argument (raw attribute), regardless of what subcommand you are in
//! - `value_enum`: Parse the value using the [`ValueEnum`][crate::ValueEnum]
//! - `skip [= <expr>]`: Ignore this field, filling in with `<expr>`
//!   - Without `<expr>`: fills the field with `Default::default()`
//! - `default_value = <str>`: [`Arg::default_value`][crate::Arg::default_value] and [`Arg::required(false)`][crate::Arg::required]
//! - `default_value_t [= <expr>]`: [`Arg::default_value`][crate::Arg::default_value] and [`Arg::required(false)`][crate::Arg::required]
//!   - Requires `std::fmt::Display` that roundtrips correctly with the
//!     [`Arg::value_parser`][crate::Arg::value_parser] or `#[arg(value_enum)]`
//!   - Without `<expr>`, relies on `Default::default()`
//! - `default_values_t = <expr>`: [`Arg::default_values`][crate::Arg::default_values] and [`Arg::required(false)`][crate::Arg::required]
//!   - Requires field arg to be of type `Vec<T>` and `T` to implement `std::fmt::Display` or `#[arg(value_enum)]`
//!   - `<expr>` must implement `IntoIterator<T>`
//! - `default_value_os_t [= <expr>]`: [`Arg::default_value_os`][crate::Arg::default_value_os] and [`Arg::required(false)`][crate::Arg::required]
//!   - Requires `std::convert::Into<OsString>` or `#[arg(value_enum)]`
//!   - Without `<expr>`, relies on `Default::default()`
//! - `default_values_os_t = <expr>`: [`Arg::default_values_os`][crate::Arg::default_values_os] and [`Arg::required(false)`][crate::Arg::required]
//!   - Requires field arg to be of type `Vec<T>` and `T` to implement `std::convert::Into<OsString>` or `#[arg(value_enum)]`
//!   - `<expr>` must implement `IntoIterator<T>`
//!
//! ### ValueEnum Attributes
//!
//! - `rename_all = <string_literal>`: Override default field / variant name case conversion for [`PossibleValue::new`][crate::builder::PossibleValue]
//!   - When not present: `"kebab-case"`
//!   - Available values: `"camelCase"`, `"kebab-case"`, `"PascalCase"`, `"SCREAMING_SNAKE_CASE"`, `"snake_case"`, `"lower"`, `"UPPER"`, `"verbatim"`
//!
//! ### Possible Value Attributes
//!
//! These correspond to a [`PossibleValue`][crate::builder::PossibleValue].
//!
//! **Raw attributes:**  Any [`PossibleValue` method][crate::builder::PossibleValue] can also be used as an attribute, see [Terminology](#terminology) for syntax.
//! - e.g. `#[value(alias("foo"))]` would translate to `pv.alias("foo")`
//!
//! **Magic attributes**:
//! - `name = <expr>`: [`PossibleValue::new`][crate::builder::PossibleValue::new]
//!   - When not present: case-converted field name is used
//! - `help = <expr>`: [`PossibleValue::help`][crate::builder::PossibleValue::help]
//!   - When not present: [Doc comment summary](#doc-comments)
//! - `skip`: Ignore this variant
//!
//! ## Arg Types
//!
//! `clap` assumes some intent based on the type used:
//!
//! | Type                | Effect                               | Implies                                                     |
//! |---------------------|--------------------------------------|-------------------------------------------------------------|
//! | `()`                | user-defined                         | `.action(ArgAction::Set).required(false)`                   |
//! | `bool`              | flag                                 | `.action(ArgAction::SetTrue)`                               |
//! | `Option<T>`         | optional argument                    | `.action(ArgAction::Set).required(false)`                   |
//! | `Option<Option<T>>` | optional value for optional argument | `.action(ArgAction::Set).required(false).num_args(0..=1)`   |
//! | `T`                 | required argument                    | `.action(ArgAction::Set).required(!has_default)`            |
//! | `Vec<T>`            | `0..` occurrences of argument        | `.action(ArgAction::Append).required(false)`  |
//! | `Option<Vec<T>>`    | `0..` occurrences of argument        | `.action(ArgAction::Append).required(false)`  |
//!
//! In addition, [`.value_parser(value_parser!(T))`][crate::value_parser!] is called for each
//! field.
//!
//! Notes:
//! - For custom type behavior, you can override the implied attributes/settings and/or set additional ones
//! - `Option<Vec<T>>` will be `None` instead of `vec![]` if no arguments are provided.
//!   - This gives the user some flexibility in designing their argument, like with `num_args(0..)`
//!
//! ## Doc Comments
//!
//! In clap, help messages for the whole binary can be specified
//! via [`Command::about`][crate::Command::about] and [`Command::long_about`][crate::Command::long_about] while help messages
//! for individual arguments can be specified via [`Arg::help`][crate::Arg::help] and [`Arg::long_help`][crate::Arg::long_help].
//!
//! `long_*` variants are used when user calls the program with
//! `--help` and "short" variants are used with `-h` flag.
//!
//! ```rust
//! # use clap::Parser;
//!
//! #[derive(Parser)]
//! #[command(about = "I am a program and I work, just pass `-h`", long_about = None)]
//! struct Foo {
//!     #[arg(short, help = "Pass `-h` and you'll see me!")]
//!     bar: String,
//! }
//! ```
//!
//! For convenience, doc comments can be used instead of raw methods
//! (this example works exactly like the one above):
//!
//! ```rust
//! # use clap::Parser;
//!
//! #[derive(Parser)]
//! /// I am a program and I work, just pass `-h`
//! struct Foo {
//!     /// Pass `-h` and you'll see me!
//!     bar: String,
//! }
//! ```
//!
//! **NOTE:** Attributes have priority over doc comments!
//!
//! **Top level doc comments always generate `Command::about/long_about` calls!**
//! If you really want to use the `Command::about/long_about` methods (you likely don't),
//! use the `about` / `long_about` attributes to override the calls generated from
//! the doc comment.  To clear `long_about`, you can use
//! `#[command(long_about = None)]`.
//!
//! ### Pre-processing
//!
//! ```rust
//! # use clap::Parser;
//! #[derive(Parser)]
//! /// Hi there, I'm Robo!
//! ///
//! /// I like beeping, stumbling, eating your electricity,
//! /// and making records of you singing in a shower.
//! /// Pay up, or I'll upload it to youtube!
//! struct Robo {
//!     /// Call my brother SkyNet.
//!     ///
//!     /// I am artificial superintelligence. I won't rest
//!     /// until I'll have destroyed humanity. Enjoy your
//!     /// pathetic existence, you mere mortals.
//!     #[arg(long, action)]
//!     kill_all_humans: bool,
//! }
//! ```
//!
//! A doc comment consists of three parts:
//! - Short summary
//! - A blank line (whitespace only)
//! - Detailed description, all the rest
//!
//! The summary corresponds with `Command::about` / `Arg::help`.  When a blank line is
//! present, the whole doc comment will be passed to `Command::long_about` /
//! `Arg::long_help`.  Or in other words, a doc may result in just a `Command::about` /
//! `Arg::help` or `Command::about` / `Arg::help` and `Command::long_about` /
//! `Arg::long_help`
//!
//! In addition, when `verbatim_doc_comment` is not present, `clap` applies some preprocessing, including:
//!
//! - Strip leading and trailing whitespace from every line, if present.
//!
//! - Strip leading and trailing blank lines, if present.
//!
//! - Interpret each group of non-empty lines as a word-wrapped paragraph.
//!
//!   We replace newlines within paragraphs with spaces to allow the output
//!   to be re-wrapped to the terminal width.
//!
//! - Strip any excess blank lines so that there is exactly one per paragraph break.
//!
//! - If the first paragraph ends in exactly one period,
//!   remove the trailing period (i.e. strip trailing periods but not trailing ellipses).
//!
//! Sometimes you don't want this preprocessing to apply, for example the comment contains
//! some ASCII art or markdown tables, you would need to preserve LFs along with
//! blank lines and the leading/trailing whitespace. When you pass use the
//! `verbatim_doc_comment` magic attribute, you  preserve
//! them.
//!
//! **Note:** Keep in mind that `verbatim_doc_comment` will *still*
//! - Remove one leading space from each line, even if this attribute is present,
//!   to allow for a space between `///` and the content.
//! - Remove leading and trailing blank lines
//!
//! ## Mixing Builder and Derive APIs
//!
//! The builder and derive APIs do not live in isolation. They can work together, which is
//! especially helpful if some arguments can be specified at compile-time while others must be
//! specified at runtime.
//!
//! ### Using derived arguments in a builder application
//!
//! When using the derive API, you can `#[command(flatten)]` a struct deriving `Args` into a struct
//! deriving `Args` or `Parser`. This example shows how you can augment a `Command` instance
//! created using the builder API with `Args` created using the derive API.
//!
//! It uses the [`Args::augment_args`][crate::Args::augment_args] method to add the arguments to
//! the `Command` instance.
//!
//! Crates such as [clap-verbosity-flag](https://github.com/rust-cli/clap-verbosity-flag) provide
//! structs that implement `Args`. Without the technique shown in this example, it would not be
//! possible to use such crates with the builder API.
//!
//! For example:
//! ```rust
#![doc = include_str!("../../examples/derive_ref/augment_args.rs")]
//! ```
//!
//! ### Using derived subcommands in a builder application
//!
//! When using the derive API, you can use `#[command(subcommand)]` inside the struct to add
//! subcommands. The type of the field is usually an enum that derived `Parser`. However, you can
//! also add the subcommands in that enum to a `Command` instance created with the builder API.
//!
//! It uses the [`Subcommand::augment_subcommands`][crate::Subcommand::augment_subcommands] method
//! to add the subcommands to the `Command` instance.
//!
//! For example:
//! ```rust
#![doc = include_str!("../../examples/derive_ref/augment_subcommands.rs")]
//! ```
//!
//! ### Adding hand-implemented subcommands to a derived application
//!
//! When using the derive API, you can use `#[command(subcommand)]` inside the struct to add
//! subcommands. The type of the field is usually an enum that derived `Parser`. However, you can
//! also implement the `Subcommand` trait manually on this enum (or any other type) and it can
//! still be used inside the struct created with the derive API. The implementation of the
//! `Subcommand` trait will use the builder API to add the subcommands to the `Command` instance
//! created behind the scenes for you by the derive API.
//!
//! Notice how in the previous example we used
//! [`augment_subcommands`][crate::Subcommand::augment_subcommands] on an enum that derived
//! `Parser`, whereas now we implement
//! [`augment_subcommands`][crate::Subcommand::augment_subcommands] ourselves, but the derive API
//! calls it automatically since we used the `#[command(subcommand)]` attribute.
//!
//! For example:
//! ```rust
#![doc = include_str!("../../examples/derive_ref/hand_subcommand.rs")]
//! ```
//!
//! ### Flattening hand-implemented args into a derived application
//!
//! When using the derive API, you can use `#[command(flatten)]` inside the struct to add arguments as
//! if they were added directly to the containing struct. The type of the field is usually an
//! struct that derived `Args`. However, you can also implement the `Args` trait manually on this
//! struct (or any other type) and it can still be used inside the struct created with the derive
//! API. The implementation of the `Args` trait will use the builder API to add the arguments to
//! the `Command` instance created behind the scenes for you by the derive API.
//!
//! Notice how in the previous example we used [`augment_args`][crate::Args::augment_args] on the
//! struct that derived `Parser`, whereas now we implement
//! [`augment_args`][crate::Args::augment_args] ourselves, but the derive API calls it
//! automatically since we used the `#[command(flatten)]` attribute.
//!
//! For example:
//! ```rust
#![doc = include_str!("../../examples/derive_ref/flatten_hand_args.rs")]
//! ```
//!
//! ## Tips
//!
//! - To get access to a [`Command`][crate::Command] call
//!   [`CommandFactory::command`][crate::CommandFactory::command] (implemented when deriving
//!   [`Parser`][crate::Parser])
//! - Proactively check for bad [`Command`][crate::Command] configurations by calling
//!   [`Command::debug_assert`][crate::Command::debug_assert] in a test
//!   ([example](../tutorial_derive/05_01_assert.rs))
//! - Always remember to [document](#doc-comments) args and commands with `#![deny(missing_docs)]`

pub mod _tutorial;
#[doc(inline)]
pub use crate::_cookbook;