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Auto merge of #82855 - jyn514:no-temporaries, r=GuillaumeGomez
Avoid temporary allocations in `render_assoc_item` `render_assoc_item` came up as very hot in a profile of rustdoc on `bevy`. This avoids some temporary allocations just to calculate the length of the header. This should be a strict improvement, since all string formatting was done twice before. cc #82845
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commit
2b8fbe6b0b
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@ -105,6 +105,10 @@ impl Buffer {
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crate fn is_for_html(&self) -> bool {
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self.for_html
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}
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crate fn reserve(&mut self, additional: usize) {
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self.buffer.reserve(additional)
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}
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}
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/// Wrapper struct for properly emitting a function or method declaration.
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@ -1009,18 +1009,25 @@ fn method(
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href(did, cx.cache()).map(|p| format!("{}#{}.{}", p.0, ty, name)).unwrap_or(anchor)
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}
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};
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let mut header_len = format!(
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"{}{}{}{}{}{:#}fn {}{:#}",
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meth.visibility.print_with_space(cx.tcx(), meth.def_id, cx.cache()),
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header.constness.print_with_space(),
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header.asyncness.print_with_space(),
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header.unsafety.print_with_space(),
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print_default_space(meth.is_default()),
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print_abi_with_space(header.abi),
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name,
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g.print(cx.cache())
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)
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.len();
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let tcx = cx.tcx();
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let vis = meth.visibility.print_with_space(tcx, meth.def_id, cx.cache()).to_string();
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let constness = header.constness.print_with_space();
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let asyncness = header.asyncness.print_with_space();
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let unsafety = header.unsafety.print_with_space();
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let defaultness = print_default_space(meth.is_default());
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let abi = print_abi_with_space(header.abi).to_string();
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// NOTE: `{:#}` does not print HTML formatting, `{}` does. So `g.print` can't be reused between the length calculation and `write!`.
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let generics_len = format!("{:#}", g.print(cx.cache())).len();
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let mut header_len = "fn ".len()
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+ vis.len()
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+ constness.len()
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+ asyncness.len()
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+ unsafety.len()
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+ defaultness.len()
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+ abi.len()
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+ name.as_str().len()
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+ generics_len;
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let (indent, end_newline) = if parent == ItemType::Trait {
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header_len += 4;
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(4, false)
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@ -1028,17 +1035,18 @@ fn method(
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(0, true)
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};
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render_attributes(w, meth, false);
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w.reserve(header_len + "<a href=\"\" class=\"fnname\">{".len() + "</a>".len());
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write!(
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w,
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"{}{}{}{}{}{}{}fn <a href=\"{href}\" class=\"fnname\">{name}</a>\
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{generics}{decl}{spotlight}{where_clause}",
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if parent == ItemType::Trait { " " } else { "" },
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meth.visibility.print_with_space(cx.tcx(), meth.def_id, cx.cache()),
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header.constness.print_with_space(),
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header.asyncness.print_with_space(),
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header.unsafety.print_with_space(),
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print_default_space(meth.is_default()),
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print_abi_with_space(header.abi),
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vis,
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constness,
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asyncness,
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unsafety,
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defaultness,
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abi,
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href = href,
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name = name,
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generics = g.print(cx.cache()),
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