Rollup merge of rust-lang#136599 - yotamofek:pr/rustdoc-more-joined, r=GuillaumeGomez

librustdoc: more usages of `Joined::joined`

Some missed opportunities from rust-lang#136244
r? ```@GuillaumeGomez``` since you reviewed the last one (feel free to re-assign, of course 😊)
First two commits are just drive-by cleanups

Author: matthiaskrgr

src/librustdoc/clean/mod.rs

@@ -1150,9 +1150,9 @@ fn clean_args_from_types_and_body_id<'tcx>(
     Arguments {
         values: types
             .iter()
-            .enumerate()
-            .map(|(i, ty)| Argument {
-                name: name_from_pat(body.params[i].pat),
+            .zip(body.params)
+            .map(|(ty, param)| Argument {
+                name: name_from_pat(param.pat),
                 type_: clean_ty(ty, cx),
                 is_const: false,
             })

src/librustdoc/clean/utils.rs

@@ -1,5 +1,5 @@
 use std::assert_matches::debug_assert_matches;
-use std::fmt::Write as _;
+use std::fmt::{self, Display, Write as _};
 use std::mem;
 use std::sync::LazyLock as Lazy;
 
@@ -24,6 +24,7 @@ use crate::clean::{
     clean_middle_ty, inline,
 };
 use crate::core::DocContext;
+use crate::display::Joined as _;
 
 #[cfg(test)]
 mod tests;
@@ -250,16 +251,20 @@ pub(crate) fn qpath_to_string(p: &hir::QPath<'_>) -> String {
         hir::QPath::LangItem(lang_item, ..) => return lang_item.name().to_string(),
     };
 
-    let mut s = String::new();
-    for (i, seg) in segments.iter().enumerate() {
-        if i > 0 {
-            s.push_str("::");
-        }
-        if seg.ident.name != kw::PathRoot {
-            s.push_str(seg.ident.as_str());
-        }
-    }
-    s
+    fmt::from_fn(|f| {
+        segments
+            .iter()
+            .map(|seg| {
+                fmt::from_fn(|f| {
+                    if seg.ident.name != kw::PathRoot {
+                        write!(f, "{}", seg.ident)?;
+                    }
+                    Ok(())
+                })
+            })
+            .joined("::", f)
+    })
+    .to_string()
 }
 
 pub(crate) fn build_deref_target_impls(
@@ -299,35 +304,49 @@ pub(crate) fn name_from_pat(p: &hir::Pat<'_>) -> Symbol {
 
     Symbol::intern(&match p.kind {
         // FIXME(never_patterns): does this make sense?
-        PatKind::Wild | PatKind::Err(_) | PatKind::Never | PatKind::Struct(..) => {
+        PatKind::Wild
+        | PatKind::Err(_)
+        | PatKind::Never
+        | PatKind::Struct(..)
+        | PatKind::Range(..) => {
             return kw::Underscore;
         }
         PatKind::Binding(_, _, ident, _) => return ident.name,
+        PatKind::Box(p) | PatKind::Ref(p, _) | PatKind::Guard(p, _) => return name_from_pat(p),
         PatKind::TupleStruct(ref p, ..)
         | PatKind::Expr(PatExpr { kind: PatExprKind::Path(ref p), .. }) => qpath_to_string(p),
         PatKind::Or(pats) => {
-            pats.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(" | ")
+            fmt::from_fn(|f| pats.iter().map(|p| name_from_pat(p)).joined(" | ", f)).to_string()
+        }
+        PatKind::Tuple(elts, _) => {
+            format!("({})", fmt::from_fn(|f| elts.iter().map(|p| name_from_pat(p)).joined(", ", f)))
         }
-        PatKind::Tuple(elts, _) => format!(
-            "({})",
-            elts.iter().map(|p| name_from_pat(p).to_string()).collect::<Vec<String>>().join(", ")
-        ),
-        PatKind::Box(p) => return name_from_pat(p),
         PatKind::Deref(p) => format!("deref!({})", name_from_pat(p)),
-        PatKind::Ref(p, _) => return name_from_pat(p),
         PatKind::Expr(..) => {
             warn!(
                 "tried to get argument name from PatKind::Expr, which is silly in function arguments"
             );
             return Symbol::intern("()");
         }
-        PatKind::Guard(p, _) => return name_from_pat(p),
-        PatKind::Range(..) => return kw::Underscore,
-        PatKind::Slice(begin, ref mid, end) => {
-            let begin = begin.iter().map(|p| name_from_pat(p).to_string());
-            let mid = mid.as_ref().map(|p| format!("..{}", name_from_pat(p))).into_iter();
-            let end = end.iter().map(|p| name_from_pat(p).to_string());
-            format!("[{}]", begin.chain(mid).chain(end).collect::<Vec<_>>().join(", "))
+        PatKind::Slice(begin, mid, end) => {
+            fn print_pat<'a>(pat: &'a Pat<'a>, wild: bool) -> impl Display + 'a {
+                fmt::from_fn(move |f| {
+                    if wild {
+                        f.write_str("..")?;
+                    }
+                    name_from_pat(pat).fmt(f)
+                })
+            }
+
+            format!(
+                "[{}]",
+                fmt::from_fn(|f| {
+                    let begin = begin.iter().map(|p| print_pat(p, false));
+                    let mid = mid.map(|p| print_pat(p, true));
+                    let end = end.iter().map(|p| print_pat(p, false));
+                    begin.chain(mid).chain(end).joined(", ", f)
+                })
+            )
         }
     })
 }

src/librustdoc/doctest/make.rs

@@ -1,6 +1,7 @@
 //! Logic for transforming the raw code given by the user into something actually
 //! runnable, e.g. by adding a `main` function if it doesn't already exist.
 
+use std::fmt::{self, Write as _};
 use std::io;
 use std::sync::Arc;
 
@@ -17,6 +18,7 @@ use rustc_span::symbol::sym;
 use tracing::debug;
 
 use super::GlobalTestOptions;
+use crate::display::Joined as _;
 use crate::html::markdown::LangString;
 
 /// This struct contains information about the doctest itself which is then used to generate
@@ -232,13 +234,15 @@ impl DocTestBuilder {
 
             // add extra 4 spaces for each line to offset the code block
             if opts.insert_indent_space {
-                prog.push_str(
-                    &everything_else
+                write!(
+                    prog,
+                    "{}",
+                    fmt::from_fn(|f| everything_else
                         .lines()
-                        .map(|line| format!("    {}", line))
-                        .collect::<Vec<String>>()
-                        .join("\n"),
-                );
+                        .map(|line| fmt::from_fn(move |f| write!(f, "    {line}")))
+                        .joined("\n", f))
+                )
+                .unwrap();
             } else {
                 prog.push_str(everything_else);
             };

src/librustdoc/html/render/print_item.rs

@@ -2,7 +2,6 @@ use std::cmp::Ordering;
 use std::fmt;
 use std::fmt::Display;
 
-use itertools::Itertools;
 use rinja::Template;
 use rustc_abi::VariantIdx;
 use rustc_data_structures::captures::Captures;
@@ -514,11 +513,7 @@ fn item_module(w: &mut String, cx: &Context<'_>, item: &clean::Item, items: &[cl
                         class = myitem.type_(),
                         unsafety_flag = unsafety_flag,
                         href = item_path(myitem.type_(), myitem.name.unwrap().as_str()),
-                        title = [myitem.type_().to_string(), full_path(cx, myitem)]
-                            .iter()
-                            .filter_map(|s| if !s.is_empty() { Some(s.as_str()) } else { None })
-                            .collect::<Vec<_>>()
-                            .join(" "),
+                        title = format_args!("{} {}", myitem.type_(), full_path(cx, myitem)),
                     ),
                 );
             }
@@ -915,7 +910,7 @@ fn item_trait(w: &mut String, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
                 w,
                 format_args!(
                     "<div class=\"stab must_implement\">At least one of the `{}` methods is required.</div>",
-                    list.iter().join("`, `")
+                    fmt::from_fn(|f| list.iter().joined("`, `", f))
                 ),
             );
         }
@@ -1168,17 +1163,18 @@ fn item_trait(w: &mut String, cx: &Context<'_>, it: &clean::Item, t: &clean::Tra
         js_src_path.extend(cx.current.iter().copied());
         js_src_path.push_fmt(format_args!("{}.{}.js", it.type_(), it.name.unwrap()));
     }
-    let extern_crates = extern_crates
-        .into_iter()
-        .map(|cnum| tcx.crate_name(cnum).to_string())
-        .collect::<Vec<_>>()
-        .join(",");
-    let (extern_before, extern_after) =
-        if extern_crates.is_empty() { ("", "") } else { (" data-ignore-extern-crates=\"", "\"") };
+    let extern_crates = fmt::from_fn(|f| {
+        if !extern_crates.is_empty() {
+            f.write_str(" data-ignore-extern-crates=\"")?;
+            extern_crates.iter().map(|&cnum| tcx.crate_name(cnum)).joined(",", f)?;
+            f.write_str("\"")?;
+        }
+        Ok(())
+    });
     write_str(
         w,
         format_args!(
-            "<script src=\"{src}\"{extern_before}{extern_crates}{extern_after} async></script>",
+            "<script src=\"{src}\"{extern_crates} async></script>",
             src = js_src_path.finish()
         ),
     );
@@ -1400,7 +1396,7 @@ fn item_type_alias(w: &mut String, cx: &Context<'_>, it: &clean::Item, t: &clean
             .collect();
         js_src_path.extend(target_fqp[..target_fqp.len() - 1].iter().copied());
         js_src_path.push_fmt(format_args!("{target_type}.{}.js", target_fqp.last().unwrap()));
-        let self_path = self_fqp.iter().map(Symbol::as_str).collect::<Vec<&str>>().join("::");
+        let self_path = fmt::from_fn(|f| self_fqp.iter().joined("::", f));
         write_str(
             w,
             format_args!(