rollup merge of #22502: nikomatsakis/deprecate-bracket-bracket

Conflicts:
	src/libcollections/slice.rs
	src/libcollections/str.rs
	src/librustc/middle/lang_items.rs
	src/librustc_back/rpath.rs
	src/librustc_typeck/check/regionck.rs
	src/libstd/ffi/os_str.rs
	src/libsyntax/diagnostic.rs
	src/libsyntax/parse/parser.rs
	src/libsyntax/util/interner.rs
	src/test/run-pass/regions-refcell.rs

src/librustdoc/html/highlight.rs

@@ -34,7 +34,7 @@ pub fn highlight(src: &str, class: Option<&str>, id: Option<&str>) -> String {
          class,
          id,
          &mut out).unwrap();
-    String::from_utf8_lossy(&out[]).into_owned()
+    String::from_utf8_lossy(&out[..]).into_owned()
 }
 
 /// Exhausts the `lexer` writing the output into `out`.