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Add
fmt::Display wrapper to pad/truncate using correct width
Fixes #9
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,157 @@ | ||
| use core::fmt::{self, Write}; | ||
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| use unicode_segmentation::UnicodeSegmentation; | ||
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| use crate::{UnicodeWidthChar, UnicodeWidthStr}; | ||
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| /// A wrapper around a [`str`] with a [`fmt::Display`] impl | ||
| /// that performs padding, truncation, and alignment based on | ||
| /// the string width according to this crate (non-CJK). | ||
| /// | ||
| /// Produced via [`UnicodeWidthStr::using_width`]; | ||
| /// see its documentation for more. | ||
| #[derive(PartialEq, Eq, Hash)] | ||
| #[repr(transparent)] | ||
| pub struct StrWithWidth(str); | ||
|
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| impl StrWithWidth { | ||
| /// The advance width of the `string` | ||
| /// (equivalent to [`UnicodeWidthStr::width`]). | ||
| #[inline] | ||
| pub fn width(&self) -> usize { | ||
| self.0.width() | ||
| } | ||
| } | ||
|
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| impl PartialEq<str> for StrWithWidth { | ||
| #[inline] | ||
| fn eq(&self, other: &str) -> bool { | ||
| &self.0 == other | ||
| } | ||
| } | ||
|
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| impl AsRef<str> for StrWithWidth { | ||
| #[inline] | ||
| fn as_ref(&self) -> &str { | ||
| &self.0 | ||
| } | ||
| } | ||
|
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| impl AsMut<str> for StrWithWidth { | ||
| #[inline] | ||
| fn as_mut(&mut self) -> &mut str { | ||
| &mut self.0 | ||
| } | ||
| } | ||
|
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| impl AsRef<StrWithWidth> for str { | ||
| #[inline] | ||
| fn as_ref(&self) -> &StrWithWidth { | ||
| // SAFETY: `repr(transparent)` ensures compatible types | ||
| unsafe { core::mem::transmute(self) } | ||
| } | ||
| } | ||
|
|
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| impl AsMut<StrWithWidth> for str { | ||
| #[inline] | ||
| fn as_mut(&mut self) -> &mut StrWithWidth { | ||
| // SAFETY: `repr(transparent)` ensures compatible types | ||
| unsafe { core::mem::transmute(self) } | ||
| } | ||
| } | ||
|
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| impl fmt::Display for StrWithWidth { | ||
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| // Fast path | ||
| if f.width().is_none() && f.precision().is_none() { | ||
| return f.write_str(&self.0); | ||
| } | ||
|
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| // Truncate the string to maximum width | ||
| let (truncated, truncated_width) = if let Some(max_width) = f.precision() { | ||
| let mut truncated_width: usize = 0; | ||
| let mut truncated = &self.0; | ||
| for (seg_offset, seg) in self.0.grapheme_indices(true) { | ||
| let new_width = truncated_width + seg.width(); | ||
| if new_width > max_width { | ||
| truncated = &self.0[..seg_offset]; | ||
| break; | ||
| } else { | ||
| truncated_width = new_width; | ||
| } | ||
| } | ||
| (truncated, truncated_width) | ||
| } else { | ||
| (&self.0, self.0.width()) | ||
| }; | ||
|
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||
| // Pad the string to minimum width | ||
| if let Some(padding) = f | ||
| .width() | ||
| .and_then(|min_width| min_width.checked_sub(truncated_width)) | ||
| .filter(|&padding| padding > 0) | ||
| { | ||
| let align = f.align().unwrap_or(fmt::Alignment::Left); | ||
|
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| let mut fill_char = f.fill(); | ||
| let mut fill_char_width = fill_char.width().unwrap_or(1); | ||
|
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| // If we try to fill with a zero-sized char, we'll never succeed, so fall back to space | ||
| if fill_char_width == 0 { | ||
| fill_char = ' '; | ||
| fill_char_width = 1; | ||
| } | ||
|
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||
| let (pre_pre_pad, pre_pad, post_pad, post_post_pad) = match align { | ||
| fmt::Alignment::Left => { | ||
| (0, 0, padding % fill_char_width, padding / fill_char_width) | ||
| } | ||
| fmt::Alignment::Right => { | ||
| (padding / fill_char_width, padding % fill_char_width, 0, 0) | ||
| } | ||
| fmt::Alignment::Center => { | ||
| let (left_padding, right_padding) = (padding / 2, (padding + 1) / 2); | ||
| let (pre_pre_pad, mut pre_pad, mut post_pad, mut post_post_pad) = { | ||
| ( | ||
| left_padding / fill_char_width, | ||
| left_padding % fill_char_width, | ||
| right_padding % fill_char_width, | ||
| right_padding / fill_char_width, | ||
| ) | ||
| }; | ||
| if let Some(diff) = pre_pad.checked_sub(fill_char_width - post_pad) { | ||
| pre_pad = 0; | ||
| post_pad = diff; | ||
| post_post_pad += 1; | ||
| } | ||
| (pre_pre_pad, pre_pad, post_pad, post_post_pad) | ||
| } | ||
| }; | ||
|
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| for _ in 0..pre_pre_pad { | ||
| f.write_char(fill_char)?; | ||
| } | ||
| for _ in 0..pre_pad { | ||
| f.write_char(' ')?; | ||
| } | ||
| f.write_str(truncated)?; | ||
| for _ in 0..post_pad { | ||
| f.write_char(' ')?; | ||
| } | ||
| for _ in 0..post_post_pad { | ||
| f.write_char(fill_char)?; | ||
| } | ||
|
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| Ok(()) | ||
| } else { | ||
| f.write_str(truncated) | ||
| } | ||
| } | ||
| } | ||
|
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| impl fmt::Debug for StrWithWidth { | ||
| #[inline] | ||
| fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| fmt::Debug::fmt(&self.0, f) | ||
| } | ||
| } |
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