Auto merge of #58578 - kennytm:rollup, r=kennytm

Rollup of 24 pull requests

Successful merges:

 - #56470 (Modify doctest's auto-`fn main()` to allow `Result`s)
 - #58044 (Make overflowing and wrapping negation const)
 - #58303 (Improve stability tags display)
 - #58336 (Fix search results interactions)
 - #58384 (Fix tables display)
 - #58392 (Use less explicit shifting in std::net::ip)
 - #58409 (rustdoc: respect alternate flag when formatting impl trait)
 - #58456 (Remove no longer accurate diagnostic code about NLL)
 - #58528 (Don't use an allocation for ItemId in StmtKind)
 - #58530 (Monomorphize less code in fs::{read|write})
 - #58534 (Mention capping forbid lints)
 - #58536 (Remove UB in pointer tests)
 - #58538 (Add missing fmt structs examples)
 - #58539 (Add alias methods to PathBuf for underlying OsString (#58234))
 - #58544 (Fix doc for rustc "-g" flag)
 - #58545 (Add regression test for a specialization-related ICE (#39448))
 - #58546 (librustc_codegen_llvm => 2018)
 - #58551 (Explain a panic in test case net::tcp::tests::double_bind)
 - #58553 (Use more impl header lifetime elision)
 - #58562 (Fix style nits)
 - #58565 (Fix typo in std::future::Future docs)
 - #58568 (Fix a transposition in driver.rs.)
 - #58569 (Reduce Some Code Repetitions like `(n << amt) >> amt`)
 - #58576 (Stabilize iter::successors and iter::from_fn)

1 files changed, 15 insertions, 11 deletions

diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 4fbbaf0f2e1..df7835214eb 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -49,8 +49,11 @@ pub struct AbiSpace(pub Abi);
 pub struct Function<'a> {
     /// The declaration to emit.
     pub decl: &'a clean::FnDecl,
-    /// The length of the function's "name", used to determine line-wrapping.
-    pub name_len: usize,
+    /// The length of the function header and name. In other words, the number of characters in the
+    /// function declaration up to but not including the parentheses.
+    ///
+    /// Used to determine line-wrapping.
+    pub header_len: usize,
     /// The number of spaces to indent each successive line with, if line-wrapping is necessary.
     pub indent: usize,
     /// Whether the function is async or not.
@@ -675,7 +678,11 @@ fn fmt_type(t: &clean::Type, f: &mut fmt::Formatter, use_absolute: bool) -> fmt:
             }
         }
         clean::ImplTrait(ref bounds) => {
-            write!(f, "impl {}", GenericBounds(bounds))
+            if f.alternate() {
+                write!(f, "impl {:#}", GenericBounds(bounds))
+            } else {
+                write!(f, "impl {}", GenericBounds(bounds))
+            }
         }
         clean::QPath { ref name, ref self_type, ref trait_ } => {
             let should_show_cast = match *trait_ {
@@ -844,7 +851,7 @@ impl fmt::Display for clean::FnDecl {
 
 impl<'a> fmt::Display for Function<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let &Function { decl, name_len, indent, asyncness } = self;
+        let &Function { decl, header_len, indent, asyncness } = self;
         let amp = if f.alternate() { "&" } else { "&amp;" };
         let mut args = String::new();
         let mut args_plain = String::new();
@@ -899,6 +906,8 @@ impl<'a> fmt::Display for Function<'a> {
             }
         }
 
+        let mut args_plain = format!("({})", args_plain);
+
         if decl.variadic {
             args.push_str(",<br> ...");
             args_plain.push_str(", ...");
@@ -917,13 +926,8 @@ impl<'a> fmt::Display for Function<'a> {
             output.to_string()
         };
 
-        let pad = " ".repeat(name_len);
-        let plain = format!("{pad}({args}){arrow}",
-                        pad = pad,
-                        args = args_plain,
-                        arrow = arrow_plain);
-
-        let output = if plain.len() > 80 {
+        let declaration_len = header_len + args_plain.len() + arrow_plain.len();
+        let output = if declaration_len > 80 {
             let full_pad = format!("<br>{}", "&nbsp;".repeat(indent + 4));
             let close_pad = format!("<br>{}", "&nbsp;".repeat(indent));
             format!("({args}{close}){arrow}",