Merging upstream version 1.75.0+dfsg1.

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

1 files changed, 153 insertions, 0 deletions

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+# Custom attributes
+The `Debug` trait supports the following attributes:
+
+* **Container attributes**
+    * [`Debug(bound="<where-clause or empty>")`](#custom-bound)
+    * [`Debug="transparent"`](#hiding-newtypes)
+* **Variant attributes**
+    * [`Debug="transparent"`](#hiding-newtypes)
+* **Field attributes**
+    * [`Debug(bound="<where-clause or empty>")`](#custom-bound)
+    * [`Debug(format_with="<path>")`](#format-with)
+    * [`Debug="ignore"`](#ignoring-a-field)
+
+# Ignoring a field
+
+You can use *derivative* to hide fields from a structure or enumeration `Debug`
+implementation:
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+#[derive(Derivative)]
+#[derivative(Debug)]
+struct Foo {
+    foo: u8,
+    #[derivative(Debug="ignore")]
+    bar: u8,
+}
+
+println!("{:?}", Foo { foo: 42, bar: 1 }); // Foo { foo: 42 }
+```
+
+# Hiding newtypes
+
+You can use *derivative* to automatically unwrap newtypes and enumeration
+variants with only one field:
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+#[derive(Derivative)]
+#[derivative(Debug="transparent")]
+struct A(isize);
+
+#[derive(Derivative)]
+#[derivative(Debug)]
+enum C {
+    Foo(u8),
+    #[derivative(Debug="transparent")]
+    Bar(u8),
+}
+
+println!("{:?}", A(42)); // 42
+println!("{:?}", C::Bar(42)); // 42
+
+// But:
+println!("{:?}", C::Foo(42)); // Foo(42)
+```
+
+# Format with
+
+You can pass a field to a format function:
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+# mod path {
+#   pub struct SomeTypeThatMightNotBeDebug;
+#   pub mod to {
+#     pub fn my_fmt_fn(_: &super::SomeTypeThatMightNotBeDebug, _: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> { unimplemented!() }
+#   }
+# }
+# use path::SomeTypeThatMightNotBeDebug;
+#[derive(Derivative)]
+#[derivative(Debug)]
+struct Foo {
+    foo: u32,
+    #[derivative(Debug(format_with="path::to::my_fmt_fn"))]
+    bar: SomeTypeThatMightNotBeDebug,
+}
+```
+
+The field `bar` will be displayed with `path::to::my_fmt_fn(&bar, &mut fmt)`
+where `fmt` is the current [`Formatter`].
+
+The function must the following prototype:
+
+```rust,ignore
+fn fmt(&T, &mut std::fmt::Formatter) -> Result<(), std::fmt::Error>;
+```
+
+# Custom bound
+
+Usually, *derivative* will add a `T: Debug` bound for each type parameter `T`
+of the current type. If you do not want that, you can specify an explicit bound:
+
+* Either on the type. This replaces all bounds:
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+# trait MyDebug {
+#   fn my_fmt(&self, _: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error>;
+# }
+# use std::fmt::Debug;
+#[derive(Derivative)]
+#[derivative(Debug(bound="T: Debug, U: MyDebug"))]
+struct Foo<T, U> {
+    foo: T,
+    #[derivative(Debug(format_with="MyDebug::my_fmt"))]
+    bar: U,
+}
+```
+
+* Or on a field. This replaces the bound *derivative* guessed for that field. The example below is equivalent to the above:
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+# trait MyDebug {
+#   fn my_fmt(&self, _: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error>;
+# }
+#[derive(Derivative)]
+#[derivative(Debug)]
+struct Foo<T, U> {
+    foo: T,
+    #[derivative(Debug(format_with="MyDebug::my_fmt", bound="U: MyDebug"))]
+    bar: U,
+}
+```
+
+With `bound=""` it is possible to remove any bound for the type. This is useful
+if your type contains a `Foo<T>` that is `Debug` even if `T` is not.
+
+[`Formatter`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html
+
+# Packed structures
+
+You can use *derivative* to implement `Debug` on packed structures. Unlike the standard `derive(debug)`, *derivative* does not require the structure itself to be `Copy`, but like the standard `derive(debug)`, it requires each (non-ignored) field to be `Copy`.
+
+```rust
+# extern crate derivative;
+# use derivative::Derivative;
+#[derive(Derivative)]
+#[derivative(Debug)]
+#[repr(C, packed)]
+struct Foo {
+    foo: u8,
+    // `String` isn't `Copy` so it must be ignored to derive `Debug`
+    #[derivative(Debug="ignore")]
+    bar: String,
+}
+```
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