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//! `pretty-trait` is a simple trait-based library for producing pretty debug output. It is //! intended to make it easy to render large tree-like structures (such as program syntax trees) in //! such a way that long items are broken across multiple lines and indented. //! //! The core feature of this crate is the [`Pretty`] trait, which represents types that can be //! pretty-printed. This crate provides a number of built-in types implementing `Pretty`, which be //! combined to implement a wide variety of formatting and layout strategies. For many purposes, //! you will not need to implement `Pretty` for your own types, but can instead convert your type //! into a structure composed out of these built-in types. //! //! # Examples //! //! Converting a custom type to built-in `Pretty` types: //! //! ``` //! use pretty_trait::{Pretty, JoinExt, Group, Indent, Sep, delimited, Conditional, to_string, block}; //! //! enum NestList { //! Atom(i32), //! List(Vec<NestList>), //! } //! //! fn to_pretty(nest_list: &NestList) -> Box<Pretty> { //! match nest_list { //! &NestList::Atom(val) => Box::new(val.to_string()), //! &NestList::List(ref children) => { //! Box::new(Group::new( //! "[" //! .join(block( //! delimited(&",".join(Sep(1)), children.iter().map(to_pretty)) //! .join(Conditional::OnlyBroken(",")), //! )).join("]"), //! )) //! } //! } //! } //! //! let max_line = Some(40); //! let tab_size = 4; //! //! let small_list = NestList::List(vec![NestList::Atom(1), NestList::Atom(2), NestList::Atom(3)]); //! assert_eq!(to_string(&to_pretty(&small_list), max_line, tab_size), "[1, 2, 3]"); //! //! let large_list = NestList::List(vec![ //! NestList::List(vec![ //! NestList::Atom(1), //! NestList::Atom(2), //! NestList::Atom(3), //! NestList::Atom(4), //! NestList::Atom(5), //! ]), //! NestList::List(vec![ //! NestList::Atom(6), //! NestList::Atom(7), //! NestList::Atom(8), //! NestList::Atom(9), //! NestList::Atom(10), //! ]), //! NestList::List(vec![ //! NestList::List(vec![NestList::Atom(11), NestList::Atom(12), NestList::Atom(13)]), //! NestList::List(vec![NestList::Atom(14), NestList::Atom(15), NestList::Atom(16)]), //! ]), //! ]); //! let expected = "\ //! [ //! [1, 2, 3, 4, 5], //! [6, 7, 8, 9, 10], //! [[11, 12, 13], [14, 15, 16]], //! ]"; //! assert_eq!(to_string(&to_pretty(&large_list), max_line, tab_size), expected); //! ``` //! //! [`Pretty`]: trait.Pretty.html use std::io; use std::ops::{Add, Mul, Deref}; use std::rc::Rc; /// Represents the number of visual columns a value would take up if it were displayed on one line, /// unless it is inherently multi-line. #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)] pub enum Size { Size(usize), MultiLine, } impl Size { fn exceeds(self, max_line: Option<usize>) -> bool { self > match max_line { Some(max) => Size::Size(max), None => Size::MultiLine, } } } impl Add<Size> for Size { type Output = Size; fn add(self, other: Size) -> Size { match (self, other) { (Size::Size(size1), Size::Size(size2)) => Size::Size(size1 + size2), _ => Size::MultiLine, } } } impl Mul<usize> for Size { type Output = Size; fn mul(self, other: usize) -> Size { match self { Size::Size(size) => Size::Size(size * other), Size::MultiLine => Size::MultiLine, } } } /// A struct used internally in pretty-printing to store information about the rendering /// environment. /// /// You only need to use this struct if you are implementing your own `Pretty` types. To render an /// existing `Pretty` type with custom line length and tab size parameters, use the `max_line` and /// `tab_size` arguments of the [`write`] or [`to_string`] functions. /// /// [`write`]: fn.write.html /// [`to_string`]: fn.to_string.html pub struct Context<'a> { /// The maximum desired line length, or `None` if lines may be of unlimited length. pub max_line: Option<usize>, /// The desired number of spaces to use for a single level of indentation. pub tab_size: usize, /// The current number of tab stops to be inserted before each new line. pub indent_level: usize, /// Whether or not the environment has been broken across multiple lines because its contents /// were too large. pub broken: bool, /// The handle to render to. pub writer: &'a mut io::Write, } impl<'a> Context<'a> { fn reborrow<'b>(&'b mut self) -> Context<'b> { Context { max_line: self.max_line, tab_size: self.tab_size, indent_level: self.indent_level, broken: self.broken, writer: &mut self.writer, } } } /// Types which can be pretty-printed. /// /// Strings implement `Pretty`, as do a number of useful built-in composable wrapper types. As /// such, you usually don't need to implement it for your own types, although you can if necessary. /// /// You usually do not need to directly call the methods defined here, unless your are implementing /// your own `Pretty` type. If you just want to render a value to a buffer or an IO handle, use one /// of the [`write`], [`println_simple`], or [`to_string`] functions instead. /// /// [`write`]: fn.write.html /// [`println_simple`]: fn.println_simple.html /// [`to_string`]: fn.to_string.html pub trait Pretty { /// Calculate the intrinsic size of this value, if it were to be displayed on a single line. fn size(&self) -> Size; /// Render this value in a given context. fn pretty_write(&self, context: Context) -> io::Result<()>; } impl<'a, T: Pretty + ?Sized> Pretty for &'a T { fn size(&self) -> Size { (*self).size() } fn pretty_write(&self, context: Context) -> io::Result<()> { (*self).pretty_write(context) } } impl<'a, T: Pretty + ?Sized> Pretty for &'a mut T { fn size(&self) -> Size { (**self).size() } fn pretty_write(&self, context: Context) -> io::Result<()> { (**self).pretty_write(context) } } impl<'a, T: Pretty + ?Sized> Pretty for Box<T> { fn size(&self) -> Size { self.deref().size() } fn pretty_write(&self, context: Context) -> io::Result<()> { self.deref().pretty_write(context) } } impl<'a, T: Pretty + ?Sized> Pretty for Rc<T> { fn size(&self) -> Size { self.deref().size() } fn pretty_write(&self, context: Context) -> io::Result<()> { self.deref().pretty_write(context) } } impl<'a> Pretty for &'a str { fn size(&self) -> Size { Size::Size(self.chars().count()) } fn pretty_write(&self, context: Context) -> io::Result<()> { write!(context.writer, "{}", self) } } impl Pretty for String { fn size(&self) -> Size { Size::Size(self.chars().count()) } fn pretty_write(&self, context: Context) -> io::Result<()> { write!(context.writer, "{}", self) } } /// A wrapper which groups its contents so they will fit onto one line if possible, even if their /// environment has been broken across multiple lines. /// /// # Examples /// /// ``` /// use pretty_trait::{JoinExt, Group, Sep, to_string}; /// /// let max_line = Some(10); /// let tab_size = 4; /// /// let expected_ungrouped = "\ /// hello /// , /// world /// !"; /// /// assert_eq!( /// to_string( /// &"hello" /// .join(Sep(0)) /// .join(",") /// .join(Sep(1)) /// .join("world") /// .join(Sep(0)) /// .join("!"), /// max_line, /// tab_size, /// ), /// expected_ungrouped /// ); /// /// let expected_grouped = "\ /// hello, /// world!"; /// /// assert_eq!( /// to_string( /// &Group::new("hello".join(Sep(0)).join(",")) /// .join(Sep(1)) /// .join(Group::new("world".join(Sep(0)).join("!"))), /// max_line, /// tab_size, /// ), /// expected_grouped, /// ); /// ``` #[derive(Clone, Copy, Debug)] pub struct Group<T> { size: Size, content: T, } impl<T: Pretty> Group<T> { pub fn new(content: T) -> Self { Group { size: content.size(), content, } } } impl<T: Pretty> Pretty for Group<T> { fn size(&self) -> Size { self.size } fn pretty_write(&self, mut context: Context) -> io::Result<()> { let indented_size = self.size + Size::Size(context.indent_level * context.tab_size); context.broken = indented_size.exceeds(context.max_line); self.content.pretty_write(context) } } /// A whitespace separator, rendered as a space if unbroken or a newline if broken. /// /// The most common uses of `Sep` are `Sep(1)`, which renders as a single space or a newline, and /// `Sep(0)`, which introduces a point where a newline will be inserted if the content is broken. /// /// # Examples /// /// Breaking into multiple lines: /// /// ``` /// use pretty_trait::{JoinExt, Sep, to_string}; /// /// let max_line = Some(10); /// let tab_size = 4; /// /// // Exceeding the line length without a separator: /// assert_eq!(to_string(&"hello".join("world!"), max_line, tab_size), "helloworld!"); /// /// let expected_broken = "\ /// hello /// world!"; /// /// assert_eq!( /// to_string(&"hello".join(Sep(0)).join("world!"), max_line, tab_size), /// expected_broken /// ); /// /// assert_eq!( /// to_string(&"hello".join(Sep(1)).join("world!"), max_line, tab_size), /// expected_broken /// ); /// ``` /// /// Introducing spaces on a single line: /// /// ``` /// # use pretty_trait::{JoinExt, Sep, to_string}; /// # let tab_size = 4; /// # /// assert_eq!( /// to_string(&"hello".join(Sep(1)).join("world!"), None, tab_size), /// "hello world!" /// ); /// /// assert_eq!( /// to_string(&"hello".join(Sep(0)).join("world!"), None, tab_size), /// "helloworld!" /// ); /// ``` #[derive(Clone, Copy, Debug)] pub struct Sep(pub usize); impl Pretty for Sep { fn size(&self) -> Size { Size::Size(self.0) } fn pretty_write(&self, context: Context) -> io::Result<()> { if context.broken { writeln!(context.writer, "")?; for _ in 0..(context.tab_size * context.indent_level) { write!(context.writer, " ")?; } } else { for _ in 0..self.0 { write!(context.writer, " ")?; } } Ok(()) } } /// An unconditional newline. /// /// Always causes its environment to break. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Newline, to_string}; /// /// let expected = "\ /// hello /// world"; /// /// assert_eq!(to_string(&"hello".join(Newline).join("world"), None, 4), expected); /// ``` #[derive(Clone, Copy, Debug)] pub struct Newline; impl Pretty for Newline { fn size(&self) -> Size { Size::MultiLine } fn pretty_write(&self, context: Context) -> io::Result<()> { writeln!(context.writer, "")?; for _ in 0..(context.tab_size * context.indent_level) { write!(context.writer, " ")?; } Ok(()) } } /// A wrapper which indents any newlines inside its contents. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Sep, Indent, to_string}; /// /// let max_line = Some(20); /// let tab_size = 4; /// /// let expected = "\ /// ( /// lorem /// ipsum /// dolor /// sit /// amet /// )"; /// /// assert_eq!( /// to_string( /// &"(".join(Indent( /// Sep(0) /// .join("lorem") /// .join(Sep(1)) /// .join("ipsum") /// .join(Sep(1)) /// .join("dolor") /// .join(Sep(1)) /// .join("sit") /// .join(Sep(1)) /// .join("amet") /// )).join(Sep(0)).join(")"), /// max_line, /// tab_size, /// ), /// expected /// ); /// ``` /// /// # Caution /// /// To indent a block enclosed in paired delimiters like brackets, care must be taken to ensure that /// the first line of the content *is* indented, and that the closing delimiter *is not* indented /// along with its contents. To ensure this, the newline after the opening delimiter should occur /// *inside* the `Indent` block, and the newline before the closing delimiter should occur *outside* /// the `Indent` block, as in the example above. The [`block`] function implements this pattern. /// /// [`block`]: fn.block.html #[derive(Clone, Copy, Debug)] pub struct Indent<T>(pub T); impl<T: Pretty> Pretty for Indent<T> { fn size(&self) -> Size { self.0.size() } fn pretty_write(&self, mut context: Context) -> io::Result<()> { context.indent_level += 1; self.0.pretty_write(context) } } /// A wrapper which concatenates two pretty-printable values. /// /// This struct is created by the [`join`] method from the `JoinExt` trait. See its documentation /// for more. /// /// [`join`]: trait.JoinExt.html#method.join #[derive(Clone, Copy, Debug)] pub struct Join<T, U>(pub T, pub U); impl<T: Pretty, U: Pretty> Pretty for Join<T, U> { fn size(&self) -> Size { self.0.size() + self.1.size() } fn pretty_write(&self, mut context: Context) -> io::Result<()> { self.0.pretty_write(context.reborrow())?; self.1.pretty_write(context)?; Ok(()) } } /// Allows `join` to be called on any `Pretty` type. /// /// This trait is automatically implemented for all `Pretty` types. It should never be implemented /// manually. pub trait JoinExt: Sized { /// Concatenate two pretty-printable values. This directly displays one after the other, with /// no separation or line breaks. For separation, use the [`Sep`] type. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, to_string}; /// /// let max_line = Some(10); /// let tab_size = 4; /// /// // Exceeds maximum line length, but does not break because there is no break-point: /// assert_eq!( /// to_string(&"hello".join("world!"), max_line, tab_size), /// "helloworld!" /// ); /// ``` /// /// [`Sep`]: struct.Sep.html fn join<U>(self, other: U) -> Join<Self, U>; } impl<T: Pretty> JoinExt for T { fn join<U>(self, other: U) -> Join<Self, U> { Join(self, other) } } /// A wrapper that concatenates an arbitrary sequence of pretty-printable values. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Sep, Seq, to_string}; /// /// let max_line = Some(10); /// let tab_size = 4; /// /// let expected = "\ /// lorem /// ipsum /// dolor /// sit /// amet"; /// /// assert_eq!( /// to_string( /// &Seq(vec![ /// "lorem".join(Some(Sep(1))), /// "ipsum".join(Some(Sep(1))), /// "dolor".join(Some(Sep(1))), /// "sit".join(Some(Sep(1))), /// "amet".join(None), /// ]), /// max_line, /// tab_size, /// ), /// expected /// ); /// ``` /// /// # Note /// /// Because a `Seq` is just a thin wrapper around a `Vec`, all of its items must be of the same /// type. When working with combinators like `join` this can sometimes be confusing. For example, /// the following code will not compile because the final element of the `Vec` does not have the /// same type as the others: /// /// ```compile_fail /// # use pretty_trait::{JoinExt, Seq, Sep}; /// Seq(vec![ /// "lorem".join(Sep(1)), /// "ipsum".join(Sep(1)), /// "dolor".join(Sep(1)), /// "sit".join(Sep(1)), /// "amet", /// ]); /// ``` #[derive(Clone, Debug)] pub struct Seq<T>(pub Vec<T>); impl<T: Pretty> Pretty for Seq<T> { fn size(&self) -> Size { self.0.iter().fold( Size::Size(0), |total, item| total + item.size(), ) } fn pretty_write(&self, mut context: Context) -> io::Result<()> { for item in &self.0 { item.pretty_write(context.reborrow())?; } Ok(()) } } /// Render a pretty-printable value to an arbitrary `io::Write` handle. /// /// This is the most general way to render a `Pretty` type. pub fn write<T: Pretty>( writer: &mut io::Write, content: &T, max_line: Option<usize>, tab_size: usize, ) -> io::Result<()> { let size = content.size(); let context = Context { max_line, tab_size, indent_level: 0, broken: size.exceeds(max_line), writer, }; content.pretty_write(context) } /// Render a pretty-printable value to an owned string and return it. /// /// If you just want to write a value to standard output, you probably want one of the more /// efficient [`println_simple`] or [`write`] functions instead. /// /// # Panics /// /// Because `Pretty` is defined in terms of writing to an `io::Write` handle, not a string, there is /// no guarantee that rendering a `Pretty` type will produce valid UTF-8. None of the built-in /// types in the `pretty-trait` crate will produce invalid UTF-8, but if a custom `Pretty` type /// generates invalid UTF-8 then this function will panic. /// /// [`println_simple`]: fn.println_simple.html /// [`write`]: fn.write.html pub fn to_string<T: Pretty>(content: &T, max_line: Option<usize>, tab_size: usize) -> String { let mut result = Vec::new(); write(&mut result, content, max_line, tab_size).expect("Writing to a string should not fail"); String::from_utf8(result).expect("Invalid UTF8") } /// Conveniently render a pretty-printable value to standard output. /// /// This function uses a default maximum line length of 80 characters, and a tab size of 2 spaces. pub fn println_simple<T: Pretty>(content: &T) { write(&mut io::stdout(), content, Some(80), 2).unwrap(); println!(""); } /// A wrapper which decides whether or not to render its contents based on the breaking mode of the /// environment. /// /// # Examples /// /// Adding a trailing comma only when broken: /// /// ``` /// use pretty_trait::{JoinExt, Sep, Conditional, to_string}; /// /// let max_line = Some(10); /// let tab_size = 4; /// /// let to_render = "lorem," /// .join(Sep(1)) /// .join("ipsum,") /// .join(Sep(1)) /// .join("dolor,") /// .join(Sep(1)) /// .join("sit,") /// .join(Sep(1)) /// .join("amet") /// .join(Conditional::OnlyBroken(",")); /// /// // Trailing comma when broken across multiple lines: /// /// let expected_broken = "\ /// lorem, /// ipsum, /// dolor, /// sit, /// amet,"; /// /// assert_eq!(to_string(&to_render, max_line, tab_size), expected_broken); /// /// // No trailing comma when rendered on a single line: /// /// assert_eq!( /// to_string(&to_render, None, tab_size), /// "lorem, ipsum, dolor, sit, amet" /// ); /// ``` #[derive(Clone, Copy, Debug)] pub enum Conditional<T> { /// Render the wrapped value under all circumstances Always(T), /// Render the wrapped value only when it appears in a multi-line context OnlyBroken(T), /// Render the wrapped value only when it appears in a single-line context OnlyUnbroken(T), } impl<T: Pretty> Pretty for Conditional<T> { fn size(&self) -> Size { Size::Size(0) } fn pretty_write(&self, context: Context) -> io::Result<()> { match (self, context.broken) { (&Conditional::Always(ref inner), _) | (&Conditional::OnlyBroken(ref inner), true) | (&Conditional::OnlyUnbroken(ref inner), false) => inner.pretty_write(context), _ => Ok(()), } } } /// An `Option` will render its contents if it is `Some`, or an empty string if it is `None`. /// /// This is useful when you need multiple pretty values to have the same type, even though they are /// not all of exactly the same form when rendered. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Seq, Sep, to_string}; /// /// let tab_size = 4; /// /// assert_eq!( /// to_string( /// &Seq(vec![ /// "lorem".join(Some(",".join(Sep(1)))), /// "ipsum".join(Some(",".join(Sep(1)))), /// "dolor".join(Some(",".join(Sep(1)))), /// "sit".join(Some(",".join(Sep(1)))), /// "amet".join(None), /// ]), /// None, /// tab_size, /// ), /// "lorem, ipsum, dolor, sit, amet" /// ); /// ``` /// /// If the above example were modified so that it did not use `Option`s, it would not compile /// because the last item in the `Seq` would have a mismatched type: /// /// ```compile_fail /// # use pretty_trait::{JoinExt, Seq, Sep}; /// Seq(vec![ /// "lorem".join(",".join(Some(Sep(1)))), /// "ipsum".join(",".join(Some(Sep(1)))), /// "dolor".join(",".join(Some(Sep(1)))), /// "sit".join(",".join(Some(Sep(1)))), /// "amet", /// ]); /// ``` impl<T: Pretty> Pretty for Option<T> { fn size(&self) -> Size { match self { &Some(ref inner) => inner.size(), &None => Size::Size(0), } } fn pretty_write(&self, context: Context) -> io::Result<()> { match self { &Some(ref inner) => inner.pretty_write(context), &None => Ok(()), } } } /// Separate a sequence of pretty-printable values by a delimiter. /// /// The delimiter is not included on the last item. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Sep, delimited, to_string}; /// /// assert_eq!( /// to_string(&delimited(&",".join(Sep(1)), &["lorem", "ipsum", "dolor"]), None, 4), /// "lorem, ipsum, dolor" /// ); /// ``` pub fn delimited<Delim, Item, It>(delim: &Delim, it: It) -> Seq<Join<Item, Option<Delim>>> where Delim: Pretty + Clone, Item: Pretty, It: IntoIterator<Item = Item>, { let mut iter = it.into_iter().peekable(); let mut results = Vec::new(); while let Some(item) = iter.next() { let cond_delim = if iter.peek().is_some() { Some(delim.clone()) } else { None }; results.push(item.join(cond_delim)); } Seq(results) } /// Wrap a pretty-printable value so that it will display as an indented block when broken across /// multiple lines. /// /// When displayed on a single line, `block` has no effect. /// /// When displayed on multiple lines, `block` inserts appropriate newlines before and after its /// content. /// /// `block(x)` is equivalent to `Indent(Sep(0).join(x)).join(Sep(0))`. /// /// # Examples /// /// Basic usage: /// /// ``` /// use pretty_trait::{JoinExt, Sep, block, to_string}; /// /// let max_line = Some(10); /// let tab_size = 2; /// /// let expected_broken = "\ /// ( /// hello /// world /// )"; /// /// let blocked = "(".join(block("hello".join(Sep(1)).join("world"))).join(")"); /// /// assert_eq!( /// to_string(&blocked, max_line, tab_size), /// expected_broken, /// ); /// /// // When displayed on one line, block has no effect: /// /// let expected_unbroken = "(hello world)"; /// /// assert_eq!( /// to_string(&blocked, None, tab_size), /// expected_unbroken, /// ); /// ``` pub fn block<T: Pretty>(content: T) -> Join<Indent<Join<Sep, T>>, Sep> { Indent(Sep(0).join(content)).join(Sep(0)) }