Add buffer abstraction

Author: Mark-Simulacrum

src/librustdoc/html/format.rs

@@ -18,6 +18,71 @@ use crate::clean::{self, PrimitiveType};
 use crate::html::item_type::ItemType;
 use crate::html::render::{self, cache, CURRENT_DEPTH};
 
+pub trait Print {
+    fn print(&self, buffer: &mut Buffer);
+}
+
+#[derive(Debug, Clone)]
+pub struct Buffer {
+    for_html: bool,
+    buffer: String,
+}
+
+impl Buffer {
+    crate fn empty_from(v: &Buffer) -> Buffer {
+        Buffer {
+            for_html: v.for_html,
+            buffer: String::new(),
+        }
+    }
+
+    crate fn html() -> Buffer {
+        Buffer {
+            for_html: true,
+            buffer: String::new(),
+        }
+    }
+
+    crate fn is_empty(&self) -> bool {
+        self.buffer.is_empty()
+    }
+
+    crate fn into_inner(self) -> String {
+        self.buffer
+    }
+
+    crate fn insert_str(&mut self, idx: usize, s: &str) {
+        self.buffer.insert_str(idx, s);
+    }
+
+    crate fn push_str(&mut self, s: &str) {
+        self.buffer.push_str(s);
+    }
+
+    // Intended for consumption by write! and writeln! (std::fmt) but without
+    // the fmt::Result return type imposed by fmt::Write (and avoiding the trait
+    // import).
+    crate fn write_str(&mut self, s: &str) {
+        self.buffer.push_str(s);
+    }
+
+    // Intended for consumption by write! and writeln! (std::fmt) but without
+    // the fmt::Result return type imposed by fmt::Write (and avoiding the trait
+    // import).
+    crate fn write_fmt(&mut self, v: fmt::Arguments<'_>) {
+        use fmt::Write;
+        self.buffer.write_fmt(v).unwrap();
+    }
+
+    crate fn display<T: fmt::Display>(&mut self, t: T) {
+        if self.for_html {
+            write!(self, "{}", t);
+        } else {
+            write!(self, "{:#}", t);
+        }
+    }
+}
+
 /// Helper to render an optional visibility with a space after it (if the
 /// visibility is preset)
 #[derive(Copy, Clone)]