Correctly handle line comments in attributes and generate extern crates

outside of wrapping function

tests/rustdoc-ui/doctest/display-output.stdout

@@ -6,7 +6,7 @@ successes:
 
 ---- $DIR/display-output.rs - foo (line 9) stdout ----
 warning: unused variable: `x`
-  --> $DIR/display-output.rs:11:5
+  --> $DIR/display-output.rs:12:5
    |
 LL | let x = 12;
    |     ^ help: if this is intentional, prefix it with an underscore: `_x`
@@ -19,13 +19,13 @@ LL | #![warn(unused)]
    = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
 
 warning: unused variable: `x`
-  --> $DIR/display-output.rs:13:8
+  --> $DIR/display-output.rs:14:8
    |
 LL | fn foo(x: &dyn std::fmt::Display) {}
    |        ^ help: if this is intentional, prefix it with an underscore: `_x`
 
 warning: function `foo` is never used
-  --> $DIR/display-output.rs:13:4
+  --> $DIR/display-output.rs:14:4
    |
 LL | fn foo(x: &dyn std::fmt::Display) {}
    |    ^^^

tests/rustdoc-ui/doctest/extern-crate.rs

@@ -0,0 +1,23 @@
+//@ check-pass
+//@ compile-flags:--test --test-args=--test-threads=1
+//@ normalize-stdout: "tests/rustdoc-ui/doctest" -> "$$DIR"
+//@ normalize-stdout: "finished in \d+\.\d+s" -> "finished in $$TIME"
+
+// This test ensures that crate imports are placed outside of the `main` function
+// so they work all the time (even in 2015 edition).
+
+/// ```rust
+/// #![feature(test)]
+///
+/// extern crate test;
+/// use test::Bencher;
+///
+/// #[bench]
+/// fn bench_xor_1000_ints(b: &mut Bencher) {
+///     b.iter(|| {
+///         (0..1000).fold(0, |old, new| old ^ new);
+///     });
+/// }
+/// ```
+///
+pub fn foo() {}

tests/rustdoc-ui/doctest/extern-crate.stdout

@@ -0,0 +1,6 @@
+
+running 1 test
+test $DIR/extern-crate.rs - foo (line 9) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+