Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+# Derive Reference
+
+1. [Overview](#overview)
+2. [Attributes](#attributes)
+    1. [Terminology](#terminology)
+    2. [Command Attributes](#command-attributes)
+    3. [Arg Attributes](#arg-attributes)
+    4. [Arg Enum Attributes](#arg-enum-attributes)
+    5. [Possible Value Attributes](#possible-value-attributes)
+3. [Arg Types](#arg-types)
+4. [Doc Comments](#doc-comments)
+5. [Tips](#tips)
+6. [Mixing Builder and Derive APIS](#mixing-builder-and-derive-apis)
+
+## Overview
+
+To derive `clap` types, you need to enable the `derive` feature flag.
+
+See [demo.rs](../demo.rs) and [demo.md](../demo.md) for a brief example.
+
+Let's start by breaking down the anatomy of the derive attributes:
+```rust
+use clap::{Parser, Args, Subcommand, ValueEnum};
+
+/// Doc comment
+#[derive(Parser)]
+#[clap(APP ATTRIBUTE)]
+struct Cli {
+    /// Doc comment
+    #[clap(ARG ATTRIBUTE)]
+    field: UserType,
+
+    #[clap(value_enum, ARG ATTRIBUTE...)]
+    field: EnumValues,
+
+    #[clap(flatten)]
+    delegate: Struct,
+
+    #[clap(subcommand)]
+    command: Command,
+}
+
+/// Doc comment
+#[derive(Args)]
+#[clap(PARENT APP ATTRIBUTE)]
+struct Struct { 
+    /// Doc comment
+    #[clap(ARG ATTRIBUTE)]
+    field: UserType,
+}
+
+/// Doc comment
+#[derive(Subcommand)]
+#[clap(PARENT APP ATTRIBUTE)]
+enum Command {
+    /// Doc comment
+    #[clap(APP ATTRIBUTE)]
+    Variant1(Struct),
+
+    /// Doc comment
+    #[clap(APP ATTRIBUTE)]
+    Variant2 {
+        /// Doc comment
+        #[clap(ARG ATTRIBUTE)]
+        field: UserType,
+    }
+}
+
+/// Doc comment
+#[derive(ValueEnum)]
+#[clap(ARG ENUM ATTRIBUTE)]
+enum EnumValues {
+    /// Doc comment
+    #[clap(POSSIBLE VALUE ATTRIBUTE)]
+    Variant1,
+}
+
+fn main() {
+    let cli = Cli::parse();
+}
+```
+
+- `Parser` parses arguments into a `struct` (arguments) or `enum` (subcommands).
+- `Args` allows defining a set of re-usable arguments that get merged into their parent container.
+- `Subcommand` defines available subcommands.
+  - Subcommand arguments can be defined in a struct-variant or automatically flattened with a tuple-variant.
+- `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 [tutorial](../tutorial_derive/README.md) and [examples](../README.md).
+
+## Attributes
+
+### Terminology
+
+**Raw attributes** are forwarded directly to the underlying `clap` builder.  Any
+`Command`, `Arg`, or `PossibleValue` method can be used as an attribute.
+
+Raw attributes come in two different syntaxes:
+```rust
+#[clap(
+    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 `clap::Command` which is used for both top-level parsers and
+when defining subcommands.
+
+**Raw attributes:**  Any [`Command` method](https://docs.rs/clap/latest/clap/type.Command.html) can also be used as an attribute, see [Terminology](#terminology) for syntax.
+- e.g. `#[clap(arg_required_else_help(true))]` would translate to `cmd.arg_required_else_help(true)`
+
+**Magic attributes:**
+- `name  = <expr>`: `clap::Command::name`
+  - When not present: [crate `name`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-name-field) (`Parser` container), variant name (`Subcommand` variant)
+- `version [= <expr>]`: `clap::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>]`: `clap::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>]`: `clap::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` container)
+    - **TIP:** When a doc comment is also present, you most likely want to add
+      `#[clap(long_about = None)]` to clear the doc comment so only `about`
+      gets shown with both `-h` and `--help`.
+- `long_about = <expr>`: `clap::Command::long_about`
+  - When not present: [Doc comment](#doc-comments) if there is a blank line, else nothing
+- `verbatim_doc_comment`: Minimizes pre-processing when converting doc comments to `about` / `long_about`
+- `next_display_order`: `clap::Command::next_display_order`
+- `next_help_heading`: `clap::Command::next_help_heading`
+  - When `flatten`ing `Args`, this is scoped to just the args in this struct and any struct `flatten`ed into it
+- `rename_all = <expr>`: Override default field / variant name case conversion for `Command::name` / `Arg::name`
+  - When not present: `kebab-case`
+  - Available values: `camelCase`, `kebab-case`, `PascalCase`, `SCREAMING_SNAKE_CASE`, `snake_case`, `lower`, `UPPER`, `verbatim`
+- `rename_all_env = <expr>`: Override default field name case conversion for env variables for  `clap::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` variants:
+- `skip`: Ignore this variant
+- `flatten`: Delegates to the variant for more subcommands (must implement `Subcommand`)
+- `subcommand`: Nest subcommands under the current set of subcommands (must implement `Subcommand`)
+- `external_subcommand`: `clap::Command::allow_external_subcommand(true)`
+  - Variant must be either `Variant(Vec<String>)` or `Variant(Vec<OsString>)`
+
+### Arg Attributes
+
+These correspond to a `clap::Arg`.
+
+**Raw attributes:**  Any [`Arg` method](https://docs.rs/clap/latest/clap/struct.Arg.html) can also be used as an attribute, see [Terminology](#terminology) for syntax.
+- e.g. `#[clap(max_values(3))]` would translate to `arg.max_values(3)`
+
+**Magic attributes**:
+- `name = <expr>`: `clap::Arg::new`
+  - When not present: case-converted field name is used
+- `value_parser [= <expr>]`: `clap::Arg::value_parser`
+  - When not present: will auto-select an implementation based on the field type
+  - To register a custom type's `ValueParser`, implement `ValueParserFactory`
+  - When present, implies `#[clap(action)]`
+- `action [= <expr>]`: `clap::Arg::action`
+  - When not present: will auto-select an action based on the field type
+  - When present, implies `#[clap(value_parser)]`
+- `help = <expr>`: `clap::Arg::help`
+  - When not present: [Doc comment summary](#doc-comments)
+- `long_help = <expr>`: `clap::Arg::long_help`
+  - When not present: [Doc comment](#doc-comments) if there is a blank line, else nothing
+- `verbatim_doc_comment`: Minimizes pre-processing when converting doc comments to `help` / `long_help`
+- `short [= <char>]`: `clap::Arg::short`
+  - When not present: no short set
+  - Without `<char>`: defaults to first character in the case-converted field name
+- `long [= <str>]`: `clap::Arg::long`
+  - When not present: no long set
+  - Without `<str>`: defaults to the case-converted field name
+- `env [= <str>]`: `clap::Arg::env` (needs `env` feature enabled)
+  - When not present: no env set
+  - Without `<str>`: defaults to the case-converted field name
+- `flatten`: Delegates to the field for more arguments (must implement `Args`)
+  - Only `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`'s Parent Command Attributes, this
+    makes reuse harder. Generally prefer putting the cmd attributes on the `Parser`
+    or on the flattened field.
+- `subcommand`: Delegates definition of subcommands to the field (must implement `Subcommand`)
+  - When `Option<T>`, the subcommand becomes optional
+- `from_global`: Read a `clap::Arg::global` argument (raw attribute), regardless of what subcommand you are in
+- `parse(<kind> [= <function>])`: `clap::Arg::validator` and `clap::ArgMatches::values_of_t`
+  - **Deprecated:**
+    - Use `value_parser(...)` for `from_str`, `try_from_str`, `from_os_str`, and `try_from_os_str`
+    - Use `action(ArgAction::Count` for `from_occurrences`
+    - Use `action(ArgAction::SetTrue` for `from_flag`
+  - Default: `try_from_str`
+  - Warning: for `Path` / `OsString`, be sure to use `try_from_os_str`
+  - See [Arg Types](#arg-types) for more details
+- `value_enum`: Parse the value using the `ValueEnum` trait
+- `skip [= <expr>]`: Ignore this field, filling in with `<expr>`
+  - Without `<expr>`: fills the field with `Default::default()`
+- `default_value = <str>`: `clap::Arg::default_value` and `clap::Arg::required(false)`
+- `default_value_t [= <expr>]`: `clap::Arg::default_value` and `clap::Arg::required(false)`
+  - Requires `std::fmt::Display` or `#[clap(value_enum)]`
+  - Without `<expr>`, relies on `Default::default()`
+- `default_value_os_t [= <expr>]`: `clap::Arg::default_value_os` and `clap::Arg::required(false)`
+  - Requires `std::convert::Into<OsString>` or `#[clap(value_enum)]`
+  - Without `<expr>`, relies on `Default::default()`
+
+### Arg Enum Attributes
+
+- `rename_all = <expr>`: Override default field / variant name case conversion for `PossibleValue::new`
+  - 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 `clap::PossibleValue`.
+
+**Raw attributes:**  Any [`PossibleValue` method](https://docs.rs/clap/latest/clap/struct.PossibleValue.html) can also be used as an attribute, see [Terminology](#terminology) for syntax.
+- e.g. `#[clap(alias("foo"))]` would translate to `pv.alias("foo")`
+
+**Magic attributes**:
+- `name = <expr>`: `clap::PossibleValue::new`
+  - When not present: case-converted field name is used
+- `help = <expr>`: `clap::PossibleValue::help`
+  - When not present: [Doc comment summary](#doc-comments)
+
+## Arg Types
+
+`clap` assumes some intent based on the type used:
+
+| Type                | Effect                               | Implies                                                          |
+|---------------------|--------------------------------------|------------------------------------------------------------------|
+| `bool`              | flag                                 | `#[clap(parse(from_flag))]`                                     |
+| `Option<T>`         | optional argument                    | `.takes_value(true).required(false)`                             |
+| `Option<Option<T>>` | optional value for optional argument | `.takes_value(true).required(false).min_values(0).max_values(1)` |
+| `T`                 | required argument                    | `.takes_value(true).required(!has_default)`                      |
+| `Vec<T>`            | `0..` occurrences of argument        | `.takes_value(true).required(false).multiple_occurrences(true)`  |
+| `Option<Vec<T>>`    | `0..` occurrences of argument        | `.takes_value(true).required(false).multiple_occurrences(true)`  |
+
+Notes:
+- For custom type behavior, you can override the implied attributes/settings and/or set additional ones
+  - For example, see [custom-bool](./custom-bool.md)
+- `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 `min_values(0)`
+
+You can then support your custom type with `#[clap(parse(<kind> [= <function>]))]`:
+
+| `<kind>`                 | Signature                             | Default `<function>`            |
+|--------------------------|---------------------------------------|---------------------------------|
+| `from_str`               | `fn(&str) -> T`                       | `::std::convert::From::from`    |
+| `try_from_str` (default) | `fn(&str) -> Result<T, E>`            | `::std::str::FromStr::from_str` |
+| `from_os_str`            | `fn(&OsStr) -> T`                     | `::std::convert::From::from`    |
+| `try_from_os_str`        | `fn(&OsStr) -> Result<T, E>`          | (no default function)           |
+| `from_occurrences`       | `fn(u64) -> T`                        | `value as T`                    |
+| `from_flag`              | `fn(bool) -> T`                       | `::std::convert::From::from`    |
+
+Notes:
+- `from_os_str`:
+  - Implies `arg.takes_value(true).allow_invalid_utf8(true)`
+- `try_from_os_str`:
+  - Implies `arg.takes_value(true).allow_invalid_utf8(true)`
+- `from_occurrences`:
+  - Implies `arg.takes_value(false).multiple_occurrences(true)`
+  - Reads from `clap::ArgMatches::occurrences_of` rather than a `get_one` function
+    - Note: operations on values, like `default_value`, are unlikely to do what you want
+- `from_flag`
+  - Implies `arg.takes_value(false)`
+  - Reads from `clap::ArgMatches::is_present` rather than a `get_one` function
+    - Note: operations on values, like `default_value`, are unlikely to do what you want
+
+**Warning:**
+- To support non-UTF8 paths, you should use `#[clap(value_parser)]` otherwise
+  `clap` will parse it as a `String` which will fail on some paths.
+
+## Doc Comments
+
+In clap, help messages for the whole binary can be specified
+via [`Command::about`] and [`Command::long_about`] while help messages
+for individual arguments can be specified via [`Arg::help`] and [`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)]
+#[clap(about = "I am a program and I work, just pass `-h`", long_about = None)]
+struct Foo {
+    #[clap(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
+`#[clap(long_about = None)]`.
+
+**TIP:** Set `#![deny(missing_docs)]` to catch missing `--help` documentation at compile time.
+
+### 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.
+    #[clap(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
+
+## Tips
+
+- To get access to a `Command` call `CommandFactory::command` (implemented when deriving `Parser`)
+- Proactively check for bad `Command` configurations by calling `Command::debug_assert` in a test ([example](../tutorial_derive/05_01_assert.rs))
+
+## 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
+
+*[Jump to source](augment_args.rs)*
+
+When using the derive API, you can `#[clap(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` 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` or `Parser`. Without the technique shown in this example, it would not be possible to use such crates with the builder API. `augment_args` to the rescue!
+
+### Using derived subcommands in a builder application
+
+*[Jump to source](augment_subcommands.rs)*
+
+When using the derive API, you can use `#[clap(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` method to add the subcommands to the `Command` instance.
+
+### Adding hand-implemented subcommands to a derived application
+
+*[Jump to source](hand_subcommand.rs)*
+
+When using the derive API, you can use `#[clap(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` on an enum that derived `Parser`, whereas now we implement `augment_subcommands` ourselves, but the derive API calls it automatically since we used the `#[clap(subcommand)]` attribute.
+
+### Flattening hand-implemented args into a derived application
+
+*[Jump to source](flatten_hand_args.rs)*
+
+When using the derive API, you can use `#[clap(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 example 1 we used `augment_args` on the struct that derived `Parser`, whereas now we implement `augment_args` ourselves, but the derive API calls it automatically since we used the `#[clap(flatten)]` attribute.