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feat(bitfield): select Unicode format with Display alt-mode (#420)
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This commit changes the generated bitfield types to default to using the
ASCII `fmt::Display` multi-line format, with the Unicode format
selectable using the alt-mode formatting specifier (`{:#}`). This is to
make it easier for downstream callers to select which format is used.

The `display_ascii()` method can be used to select ASCII only regardless
of a downstream caller's format specifier, and a similar
`display_unicode()` method is added to guarantee Unicode formatting.

I don't think this should be considered a breaking change, since
existing code will still compile, and I don't consider the output of
human-readable formats not intended for machine consumption to be part
of the semver API surface. But, it will change the default behavior...
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@hawkw
hawkw committed Apr 9, 2023
1 parent d011cf1 commit 84810d8
Showing 1 changed file with 77 additions and 78 deletions.
155 changes: 77 additions & 78 deletions bitfield/src/bitfield.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,8 @@
/// | `fn get<U>(&self, packer: Self::Packer<U>) -> U` | Given one of this type's generated packing specs for a `U`-typed value, unpacks the bit range represented by that value as a `U` and returns it. This method panics if the requested bit range does not contain a valid bit pattern for a `U`-typed value, as determined by `U`'s implementation of the [`FromBits`] trait. |
/// | `fn try_get<U>(&self, packer: Self::Packer<U>) -> Result<U, <U as FromBits>::Error>` | Like `get`, but returns a `Result` instead of panicking. |
/// | `fn assert_valid()` | Asserts that the generated bitfield type is valid. This is primarily intended to be used in tests; the macro cannot generate tests for a bitfield type on its own, so a test that simply calls `assert_valid` can be added to check the bitfield type's validity. |
/// | `fn display_ascii(&self) -> impl core::fmt::Display` | Returns a `Display` implementation that formats the bitfield in a multi-line format, using only ASCII characters. See [here](#example-ascii-display-output) for examples of this format. |
/// | `fn display_ascii(&self) -> impl core::fmt::Display` | Returns a `Display` implementation that formats the bitfield in a multi-line format, using only ASCII characters. See [here](#example-display-output) for examples of this format. |
/// | `fn display_unicode(&self) -> impl core::fmt::Display` | Returns a `Display` implementation that formats the bitfield in a multi-line format, always using Unicode box-drawing characters. See [here](#example-display-output) for examples of this format. |
///
/// The visibility of these methods depends on the visibility of the bitfield
/// struct --- if the struct is defined as `pub(crate) struct MyBitfield<u16> {
Expand Down Expand Up @@ -207,8 +208,14 @@
///
/// ## Example `Display` Output
///
/// Bitfields will automatically generate a pretty [`fmt::Display`]
/// implementation:
/// Bitfields will automatically generate a pretty, multi-line [`fmt::Display`]
/// implementation. The default [`fmt::Display`] specifier uses only ASCII
/// characters, but when Unicode box-drawing characters are also available, the
/// alternate (`{:#}`) [`fmt::Display`] specifier may be used to select a
/// `Display` implementation that uses those characters, and is (in my opinion)
/// even prettier than the default.
///
/// For example:
///
/// ```
/// # use mycelium_bitfield::{bitfield, FromBits};
Expand Down Expand Up @@ -247,9 +254,24 @@
/// # pub const A_BYTE: u8;
/// # }
/// # }
///
/// // Create an example bitfield.
/// let my_bitfield = TypedBitfield::from_bits(0b0011_0101_1001_1110);
/// let formatted = format!("{my_bitfield}");
///
/// // The default `Display` implementation uses only ASCII characters:
/// let formatted_ascii = format!("{my_bitfield}");
/// let expected = r#"
/// 00000000000000000011010110011110
///..............................10 ENUM_VALUE: Baz
///........................100111.. SOME_BITS: 39
///.......................1........ FLAG_1: true
///......................0......... FLAG_2: false
///..............00001101.......... A_BYTE: 13
/// "#.trim_start();
/// assert_eq!(formatted_ascii, expected);
///
/// // The alternate `Display` format uses Unicode box-drawing characters,
/// // and looks even nicer:
/// let formatted_unicode = format!("{my_bitfield:$}");
/// let expected = r#"
/// 00000000000000000011010110011110
/// └┬─────┘││└┬───┘└┤
Expand All @@ -259,75 +281,17 @@
/// │ └──────────── FLAG_2: false (0)
/// └─────────────────── A_BYTE: 13 (00001101)
/// "#.trim_start();
/// assert_eq!(formatted, expected);
/// assert_eq!(formatted_unicode, expected);
/// ```
///
/// ## Example ASCII-Only `Display` Output
///
/// The [`fmt::Display`] implementation for bitfields uses Unicode box-drawing
/// characters. In some contexts, where unicode is not supported or box-drawing
/// characters are not rendered nicely, it may be desirable to use an ASCII-only
/// version of the multi-line format, instead. Therefore, in addition to the
/// `Display` implementation, bitfield types also generate a `display_ascii`
/// method, which returns an `impl fmt::Display` value that renders the bitfield
/// in an ASCII-only format.
///
/// The ASCII-only format also uses slightly fewer horizontal characters than
/// the Unicode box-drawing format, so it may also be useful in cases where
/// text fields have limited width.
/// For situations where the use of ASCII or Unicode formats is always desired
/// regardless of the behavior of an upstream formatter (e.g., when returning a
/// `fmt::Display` value that doesn't know what format specifier will be used),
/// bitfield types also generate `display_ascii()` and `display_unicode()`
/// methods. These methods return `impl fmt::Display` values that *always*
/// select either the ASCII or Unicode `Display` implementations explicitly,
/// regardless of whether or not the alternate formatting specifier is used.
///
/// For example:
///
/// ```
/// # use mycelium_bitfield::{bitfield, FromBits};
/// #
/// # #[repr(u8)]
/// # #[derive(Debug, Eq, PartialEq)]
/// # enum MyEnum {
/// # Foo = 0b00,
/// # Bar = 0b01,
/// # Baz = 0b10,
/// # }
/// #
/// # impl FromBits<u32> for MyEnum {
/// # const BITS: u32 = 2;
/// # type Error = &'static str;
/// #
/// # fn try_from_bits(bits: u32) -> Result<Self, Self::Error> {
/// # match bits as u8 {
/// # bits if bits == Self::Foo as u8 => Ok(Self::Foo),
/// # bits if bits == Self::Bar as u8 => Ok(Self::Bar),
/// # bits if bits == Self::Baz as u8 => Ok(Self::Baz),
/// # _ => Err("expected one of 0b00, 0b01, or 0b10"),
/// # }
/// # }
/// #
/// # fn into_bits(self) -> u32 {
/// # self as u8 as u32
/// # }
/// # }
/// # bitfield! {
/// # pub struct TypedBitfield<u32> {
/// # const ENUM_VALUE: MyEnum;
/// # pub const SOME_BITS = 6;
/// # pub const FLAG_1: bool;
/// # pub const FLAG_2: bool;
/// # pub const A_BYTE: u8;
/// # }
/// # }
/// let my_bitfield = TypedBitfield::from_bits(0b0011_0101_1001_1110);
/// let formatted = format!("{}", my_bitfield.display_ascii());
/// println!("{}", formatted);
/// let expected = r#"
/// 00000000000000000011010110011110
///..............................10 ENUM_VALUE: Baz
///........................100111.. SOME_BITS: 39
///.......................1........ FLAG_1: true
///......................0......... FLAG_2: false
///..............00001101.......... A_BYTE: 13
/// "#.trim_start();
/// assert_eq!(formatted, expected);
/// ```
/// [`fmt::Debug`]: core::fmt::Debug
/// [`fmt::Display`]: core::fmt::Display
/// [`fmt::Binary`]: core::fmt::Binary
Expand Down Expand Up @@ -471,6 +435,12 @@ macro_rules! bitfield {

/// Returns a value that formats this bitfield in a multi-line
/// format, using only ASCII characters.
///
/// This is equivalent to formatting this bitfield using a `{}`
/// display specifier, but will *never* use Unicode box-drawing
/// characters, even when an upstream formatter uses the `{:#}`
/// `fmt::Display` specifier. This is intended for use on platforms
/// where Unicode box drawing characters are never available.
$vis fn display_ascii(&self) -> impl core::fmt::Display {
struct DisplayAscii($Name);
impl core::fmt::Display for DisplayAscii {
Expand All @@ -481,6 +451,24 @@ macro_rules! bitfield {
DisplayAscii(*self)
}

/// Returns a value that formats this bitfield in a multi-line
/// format, always using Unicode box-drawing characters.
///
/// This is equivalent to formatting this bitfield using a `{:#}`
/// format specifier, but will *always* use Unicode box-drawing
/// characters, even when an upstream formatter uses the `{}`
/// `fmt::Display` specifier.
$vis fn display_unicode(&self) -> impl core::fmt::Display {
struct DisplayUnicode($Name);
impl core::fmt::Display for DisplayUnicode {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
self.0.fmt_unicode(f)
}
}
DisplayUnicode(*self)
}


fn fmt_ascii(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
f.pad("")?;
writeln!(f, "{:0width$b}", self.0, width = $T::BITS as usize)?;
Expand All @@ -507,11 +495,8 @@ macro_rules! bitfield {

Ok(())
}
}

#[automatically_derived]
impl core::fmt::Display for $Name {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
fn fmt_unicode(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
f.pad("")?;
writeln!(f, "{:0width$b}", self.0, width = $T::BITS as usize)?;
f.pad("")?;
Expand Down Expand Up @@ -610,6 +595,17 @@ macro_rules! bitfield {
}
}

#[automatically_derived]
impl core::fmt::Display for $Name {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
if f.alternate() {
self.fmt_unicode(f)
} else {
self.fmt_ascii(f)
}
}
}

#[automatically_derived]
impl core::fmt::Binary for $Name {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
Expand Down Expand Up @@ -850,7 +846,12 @@ mod tests {
.with(TestBitfield::LOTS, 0b11010)
.with(TestBitfield::OF, 0)
.with(TestBitfield::FUN, 9);
println!("{test_bitfield}\n");

let ascii = test_bitfield.to_string();
assert_eq!(ascii, test_bitfield.display_ascii().to_string());

println!("test ASCII display:\n{ascii}");
println!("test unicode display:\n{test_bitfield:#}\n");

let test_debug = TestDebug {
value: 42,
Expand All @@ -860,8 +861,6 @@ mod tests {
println!("test_debug(alt): {test_debug:#?}\n");

println!("test_debug: {test_debug:?}\n");

println!("test ASCII display:\n{}", test_bitfield.display_ascii());
}

#[test]
Expand Down

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