Rollup merge of rust-lang#146838 - yotamofek:pr/rustdoc/wrappers, r=lolbinarycat

Introduce "wrapper" helpers to rustdoc

Add a few traits for streamlining places where we need to wrap certain `fmt::Display`s in stuff like parentheses or brackets.
Hopefully this makes the actual display logic slightly easier to read.

First two commits are small, unrelated cleanups.

I'll probably add some doc comments to the stuff in `display.rs`, maybe also play around with the API, but wanted to get feedback on this idea first.

Author: Zalathar

src/librustdoc/clean/cfg.rs

@@ -3,16 +3,16 @@
 // FIXME: Once the portability lint RFC is implemented (see tracking issue #41619),
 // switch to use those structures instead.
 
-use std::fmt::{self, Write};
-use std::{mem, ops};
+use std::{fmt, mem, ops};
 
+use itertools::Either;
 use rustc_ast::{LitKind, MetaItem, MetaItemInner, MetaItemKind, MetaItemLit};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_session::parse::ParseSess;
 use rustc_span::Span;
 use rustc_span::symbol::{Symbol, sym};
 
-use crate::display::Joined as _;
+use crate::display::{Joined as _, MaybeDisplay, Wrapped};
 use crate::html::escape::Escape;
 
 #[cfg(test)]
@@ -376,27 +376,20 @@ impl Format {
             Format::LongPlain => false,
         }
     }
+
+    fn escape(self, s: &str) -> impl fmt::Display {
+        if self.is_html() { Either::Left(Escape(s)) } else { Either::Right(s) }
+    }
 }
 
 /// Pretty-print wrapper for a `Cfg`. Also indicates what form of rendering should be used.
 struct Display<'a>(&'a Cfg, Format);
 
-fn write_with_opt_paren<T: fmt::Display>(
-    fmt: &mut fmt::Formatter<'_>,
-    has_paren: bool,
-    obj: T,
-) -> fmt::Result {
-    if has_paren {
-        fmt.write_char('(')?;
-    }
-    obj.fmt(fmt)?;
-    if has_paren {
-        fmt.write_char(')')?;
+impl Display<'_> {
+    fn code_wrappers(&self) -> Wrapped<&'static str> {
+        if self.1.is_html() { Wrapped::with("<code>", "</code>") } else { Wrapped::with("`", "`") }
     }
-    Ok(())
-}
 
-impl Display<'_> {
     fn display_sub_cfgs(
         &self,
         fmt: &mut fmt::Formatter<'_>,
@@ -427,20 +420,17 @@ impl Display<'_> {
             sub_cfgs
                 .iter()
                 .map(|sub_cfg| {
-                    fmt::from_fn(move |fmt| {
-                        if let Cfg::Cfg(_, Some(feat)) = sub_cfg
-                            && short_longhand
-                        {
-                            if self.1.is_html() {
-                                write!(fmt, "<code>{feat}</code>")?;
-                            } else {
-                                write!(fmt, "`{feat}`")?;
-                            }
-                        } else {
-                            write_with_opt_paren(fmt, !sub_cfg.is_all(), Display(sub_cfg, self.1))?;
-                        }
-                        Ok(())
-                    })
+                    if let Cfg::Cfg(_, Some(feat)) = sub_cfg
+                        && short_longhand
+                    {
+                        Either::Left(self.code_wrappers().wrap(feat))
+                    } else {
+                        Either::Right(
+                            Wrapped::with_parens()
+                                .when(!sub_cfg.is_all())
+                                .wrap(Display(sub_cfg, self.1)),
+                        )
+                    }
                 })
                 .joined(separator, f)
         })
@@ -461,9 +451,9 @@ impl fmt::Display for Display<'_> {
                 sub_cfgs
                     .iter()
                     .map(|sub_cfg| {
-                        fmt::from_fn(|fmt| {
-                            write_with_opt_paren(fmt, !sub_cfg.is_all(), Display(sub_cfg, self.1))
-                        })
+                        Wrapped::with_parens()
+                            .when(!sub_cfg.is_all())
+                            .wrap(Display(sub_cfg, self.1))
                     })
                     .joined(separator, fmt)
             }
@@ -568,21 +558,13 @@ impl fmt::Display for Display<'_> {
                 };
                 if !human_readable.is_empty() {
                     fmt.write_str(human_readable)
-                } else if let Some(v) = value {
-                    if self.1.is_html() {
-                        write!(
-                            fmt,
-                            r#"<code>{}="{}"</code>"#,
-                            Escape(name.as_str()),
-                            Escape(v.as_str())
-                        )
-                    } else {
-                        write!(fmt, r#"`{name}="{v}"`"#)
-                    }
-                } else if self.1.is_html() {
-                    write!(fmt, "<code>{}</code>", Escape(name.as_str()))
                 } else {
-                    write!(fmt, "`{name}`")
+                    let value = value
+                        .map(|v| fmt::from_fn(move |f| write!(f, "={}", self.1.escape(v.as_str()))))
+                        .maybe_display();
+                    self.code_wrappers()
+                        .wrap(format_args!("{}{value}", self.1.escape(name.as_str())))
+                        .fmt(fmt)
                 }
             }
         }

src/librustdoc/display.rs

@@ -1,6 +1,6 @@
 //! Various utilities for working with [`fmt::Display`] implementations.
 
-use std::fmt::{self, Display, Formatter};
+use std::fmt::{self, Display, Formatter, FormattingOptions};
 
 pub(crate) trait Joined: IntoIterator {
     /// Takes an iterator over elements that implement [`Display`], and format them into `f`, separated by `sep`.
@@ -45,3 +45,87 @@ impl<T: Display> MaybeDisplay for Option<T> {
         })
     }
 }
+
+#[derive(Clone, Copy)]
+pub(crate) struct Wrapped<T> {
+    prefix: T,
+    suffix: T,
+}
+
+pub(crate) enum AngleBracket {
+    Open,
+    Close,
+}
+
+impl Display for AngleBracket {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.write_str(match (self, f.alternate()) {
+            (Self::Open, true) => "<",
+            (Self::Open, false) => "&lt;",
+            (Self::Close, true) => ">",
+            (Self::Close, false) => "&gt;",
+        })
+    }
+}
+
+impl Wrapped<AngleBracket> {
+    pub(crate) fn with_angle_brackets() -> Self {
+        Self { prefix: AngleBracket::Open, suffix: AngleBracket::Close }
+    }
+}
+
+impl Wrapped<char> {
+    pub(crate) fn with_parens() -> Self {
+        Self { prefix: '(', suffix: ')' }
+    }
+
+    pub(crate) fn with_square_brackets() -> Self {
+        Self { prefix: '[', suffix: ']' }
+    }
+}
+
+impl<T: Display> Wrapped<T> {
+    pub(crate) fn with(prefix: T, suffix: T) -> Self {
+        Self { prefix, suffix }
+    }
+
+    pub(crate) fn when(self, if_: bool) -> Wrapped<impl Display> {
+        Wrapped {
+            prefix: if_.then_some(self.prefix).maybe_display(),
+            suffix: if_.then_some(self.suffix).maybe_display(),
+        }
+    }
+
+    pub(crate) fn wrap_fn(
+        self,
+        content: impl Fn(&mut Formatter<'_>) -> fmt::Result,
+    ) -> impl Display {
+        fmt::from_fn(move |f| {
+            self.prefix.fmt(f)?;
+            content(f)?;
+            self.suffix.fmt(f)
+        })
+    }
+
+    pub(crate) fn wrap<C: Display>(self, content: C) -> impl Display {
+        self.wrap_fn(move |f| content.fmt(f))
+    }
+}
+
+#[derive(Clone, Copy)]
+pub(crate) struct WithOpts {
+    opts: FormattingOptions,
+}
+
+impl WithOpts {
+    pub(crate) fn from(f: &Formatter<'_>) -> Self {
+        Self { opts: f.options() }
+    }
+
+    pub(crate) fn display(self, t: impl Display) -> impl Display {
+        fmt::from_fn(move |f| {
+            let mut f = f.with_options(self.opts);
+            t.fmt(&mut f)
+        })
+    }
+}