Auto merge of #29544 - Ryman:reduce_doc_warnings, r=steveklabnik

Did this alphabetically, so I didn't see [how `std` was doing things](https://dxr.mozilla.org/rust/source/src/libstd/lib.rs#215) till I was nearly finished. If you prefer to add crate-level-whitelists like std instead of test-level, I can rebase with that strategy.

A number of these commits can probably be dropped as the crates don't have much to test, and are deprecated. Let me know which if any to drop! (can also squash after review if desired)

r? @steveklabnik

Author: bors

mk/tests.mk

@@ -25,7 +25,8 @@ $(eval $(call RUST_CRATE,collectionstest))
 TEST_TARGET_CRATES = $(filter-out core rustc_unicode alloc_system libc \
 		     		  alloc_jemalloc,$(TARGET_CRATES)) \
 			collectionstest coretest
-TEST_DOC_CRATES = $(DOC_CRATES)
+TEST_DOC_CRATES = $(DOC_CRATES) arena flate fmt_macros getopts graphviz \
+                log rand rbml serialize syntax term test
 TEST_HOST_CRATES = $(filter-out rustc_typeck rustc_borrowck rustc_resolve \
 		   		rustc_trans rustc_lint,\
                      $(HOST_CRATES))

src/doc/trpl/documentation.md

@@ -620,6 +620,18 @@ You can control a few aspects of the HTML that `rustdoc` generates through the
 
 This sets a few different options, with a logo, favicon, and a root URL.
 
+### Configuring documentation tests
+
+You can also configure the way that `rustdoc` tests your documentation examples
+through the `#![doc(test(..))]` attribute.
+
+```rust
+#![doc(test(attr(allow(unused_variables), deny(warnings))))]
+```
+
+This allows unused variables within the examples, but will fail the test for any
+other lint warning thrown.
+
 ## Generation options
 
 `rustdoc` also contains a few other options on the command line, for further customization:

src/liballoc/lib.rs

@@ -70,7 +70,7 @@
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
        html_root_url = "https://doc.rust-lang.org/nightly/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
-       test(no_crate_inject))]
+       test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 #![no_std]
 #![cfg_attr(not(stage0), needs_allocator)]
 

src/libarena/lib.rs

@@ -28,7 +28,8 @@
 #![crate_type = "dylib"]
 #![doc(html_logo_url = "https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
        html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
-       html_root_url = "https://doc.rust-lang.org/nightly/")]
+       html_root_url = "https://doc.rust-lang.org/nightly/",
+       test(no_crate_inject, attr(deny(warnings))))]
 
 #![feature(alloc)]
 #![feature(box_syntax)]

src/libcollections/binary_heap.rs

@@ -233,6 +233,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// ```
     /// #![feature(binary_heap_extras)]
+    /// # #![allow(deprecated)]
     ///
     /// use std::collections::BinaryHeap;
     /// let heap = BinaryHeap::from_vec(vec![9, 1, 2, 7, 3, 2]);

src/libcollections/borrow.rs

@@ -72,6 +72,7 @@ impl<T> ToOwned for T where T: Clone {
 /// ```
 /// use std::borrow::Cow;
 ///
+/// # #[allow(dead_code)]
 /// fn abs_all(input: &mut Cow<[i32]>) {
 ///     for i in 0..input.len() {
 ///         let v = input[i];

src/libcollections/btree/set.rs

@@ -89,6 +89,7 @@ impl<T: Ord> BTreeSet<T> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(unused_mut)]
     /// use std::collections::BTreeSet;
     ///
     /// let mut set: BTreeSet<i32> = BTreeSet::new();

src/libcollections/fmt.rs

@@ -150,6 +150,7 @@
 //! implement a method of the signature:
 //!
 //! ```
+//! # #![allow(dead_code)]
 //! # use std::fmt;
 //! # struct Foo; // our custom type
 //! # impl fmt::Display for Foo {
@@ -174,7 +175,6 @@
 //! like:
 //!
 //! ```
-//! #![feature(fmt_flags)]
 //! use std::fmt;
 //!
 //! #[derive(Debug)]
@@ -288,6 +288,7 @@
 //! off, some example usage is:
 //!
 //! ```
+//! # #![allow(unused_must_use)]
 //! use std::fmt;
 //! use std::io::{self, Write};
 //!

src/libcollections/lib.rs

@@ -27,7 +27,7 @@
        html_root_url = "https://doc.rust-lang.org/nightly/",
        html_playground_url = "https://play.rust-lang.org/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
-       test(no_crate_inject))]
+       test(no_crate_inject, attr(allow(unused_variables), deny(warnings))))]
 
 #![allow(trivial_casts)]
 #![cfg_attr(test, allow(deprecated))] // rand

src/libcollections/slice.rs

@@ -852,6 +852,7 @@ pub trait SliceConcatExt<T: ?Sized> {
     /// # Examples
     ///
     /// ```
+    /// # #![allow(deprecated)]
     /// assert_eq!(["hello", "world"].connect(" "), "hello world");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]