Implement Print for FnOnce(&mut Buffer)

This means that callers can pass in a closure like
`|buf| some_function(..., &mut buf)` and pass in arbitrary arguments to
that function without complicating the trait definition. We also keep
the impl for str and String, since it's useful to be able to just pass
in "" or format!("{}"...) results in some cases.

This changes Print's definition to take self, instead of &self, because
otherwise FnOnce cannot be called directly. We could instead take FnMut
or even Fn, but that seems like it'd merely complicate matters -- most
of the time, the FnOnce does not constrain us at all anyway. If it does,
a custom Print impl for &'_ SomeStruct is not all that painful.

4 files changed, 18 insertions, 16 deletions

diff --git a/src/librustdoc/html/format.rs b/src/librustdoc/html/format.rs
index 99ddbcd7170..5d86f056611 100644
--- a/src/librustdoc/html/format.rs
+++ b/src/librustdoc/html/format.rs
@@ -19,23 +19,25 @@ use crate::html::item_type::ItemType;
 use crate::html::render::{self, cache, CURRENT_DEPTH};
 
 pub trait Print {
-    fn print(&self, buffer: &mut Buffer);
+    fn print(self, buffer: &mut Buffer);
 }
 
-impl<T: ?Sized + Print> Print for &'_ T {
-    fn print(&self, buffer: &mut Buffer) {
-        (&**self).print(buffer)
+impl<F> Print for F
+    where F: FnOnce(&mut Buffer),
+{
+    fn print(self, buffer: &mut Buffer) {
+        (self)(buffer)
     }
 }
 
 impl Print for String {
-    fn print(&self, buffer: &mut Buffer) {
-        buffer.write_str(self);
+    fn print(self, buffer: &mut Buffer) {
+        buffer.write_str(&self);
     }
 }
 
-impl Print for str {
-    fn print(&self, buffer: &mut Buffer) {
+impl Print for &'_ str {
+    fn print(self, buffer: &mut Buffer) {
         buffer.write_str(self);
     }
 }
@@ -92,7 +94,7 @@ impl Buffer {
         self.buffer.write_fmt(v).unwrap();
     }
 
-    crate fn to_display<T: ?Sized + Print>(mut self, t: &T) -> String {
+    crate fn to_display<T: Print>(mut self, t: T) -> String {
         t.print(&mut self);
         self.into_inner()
     }
diff --git a/src/librustdoc/html/layout.rs b/src/librustdoc/html/layout.rs
index 38dcfbfcec4..1202f411f91 100644
--- a/src/librustdoc/html/layout.rs
+++ b/src/librustdoc/html/layout.rs
@@ -34,7 +34,7 @@ pub struct Page<'a> {
 pub fn render<T: fmt::Display, S: Print>(
     layout: &Layout,
     page: &Page<'_>,
-    sidebar: &S,
+    sidebar: S,
     t: &T,
     themes: &[PathBuf],
 ) -> String {
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 40e7081c57c..fc7038f8bda 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -1174,7 +1174,7 @@ themePicker.onblur = handleThemeButtonsBlur;
                                     })
                                     .collect::<String>());
             let v = layout::render(&cx.shared.layout,
-                           &page, &(""), &content,
+                           &page, "", &content,
                            &cx.shared.themes);
             cx.shared.fs.write(&dst, v.as_bytes())?;
         }
@@ -1921,7 +1921,7 @@ impl Context {
             String::new()
         };
         let v = layout::render(&self.shared.layout,
-                       &page, &sidebar, &all,
+                       &page, sidebar, &all,
                        &self.shared.themes);
         self.shared.fs.write(&final_file, v.as_bytes())?;
 
@@ -1937,7 +1937,7 @@ impl Context {
         themes.push(PathBuf::from("settings.css"));
         let v = layout::render(
             &self.shared.layout,
-            &page, &sidebar, &settings,
+            &page, sidebar, &settings,
             &themes);
         self.shared.fs.write(&settings_file, v.as_bytes())?;
 
@@ -1994,7 +1994,7 @@ impl Context {
 
         if !self.render_redirect_pages {
             layout::render(&self.shared.layout, &page,
-                           &Sidebar{ cx: self, item: it },
+                           Sidebar{ cx: self, item: it },
                            &Item{ cx: self, item: it },
                            &self.shared.themes)
         } else {
@@ -4267,7 +4267,7 @@ fn item_foreign_type(w: &mut fmt::Formatter<'_>, cx: &Context, it: &clean::Item)
 }
 
 impl Print for Sidebar<'_> {
-    fn print(&self, buffer: &mut Buffer) {
+    fn print(self, buffer: &mut Buffer) {
         let cx = self.cx;
         let it = self.item;
         let parentlen = cx.current.len() - if it.is_mod() {1} else {0};
diff --git a/src/librustdoc/html/sources.rs b/src/librustdoc/html/sources.rs
index 018db3f9363..94ae1422609 100644
--- a/src/librustdoc/html/sources.rs
+++ b/src/librustdoc/html/sources.rs
@@ -120,7 +120,7 @@ impl<'a> SourceCollector<'a> {
             static_extra_scripts: &[&format!("source-script{}", self.scx.resource_suffix)],
         };
         let v = layout::render(&self.scx.layout,
-                       &page, &(""), &Source(contents),
+                       &page, "", &Source(contents),
                        &self.scx.themes);
         self.scx.fs.write(&cur, v.as_bytes())?;
         self.scx.local_sources.insert(p.clone(), href);