Auto merge of #27891 - steveklabnik:rollup, r=steveklabnik

- Successful merges: #27881, #27882, #27883, #27884, #27888
- Failed merges: 

5 files changed, 85 insertions, 7 deletions

diff --git a/README.md b/README.md
index 0ae93380e59..391ada0efef 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,28 @@ Read ["Installing Rust"] from [The Book].
    $ make && make install
    ```
 
+## Building Documentation
+
+If you’d like to build the documentation, it’s almost the same:
+
+```sh
+./configure
+$ make docs
+```
+
+Building the documentation requires building the compiler, so the above
+details will apply. Once you have the compiler built, you can
+
+```sh
+$ make docs NO_REBUILD=1 
+```
+
+To make sure you don’t re-build the compiler because you made a change
+to some documentation.
+
+The generated documentation will appear in a top-level `doc` directory,
+created by the `make` rule.
+
 ## Notes
 
 Since the Rust compiler is written in Rust, it must be built by a
diff --git a/man/rustc.1 b/man/rustc.1
index 0cb1c5dc32b..3ac79ecae64 100644
--- a/man/rustc.1
+++ b/man/rustc.1
@@ -41,7 +41,7 @@ look for anything here (the default)
 .RE
 .TP
 \fB\-l\fR [\fIKIND\fR=]\fINAME\fR
-Link the generated crate(s) to the specified native library \fINAME\fR.
+Link the generated crate(s) to the specified library \fINAME\fR.
 The optional \fIKIND\fR can be one of \fIstatic\fR, \fIdylib\fR, or
 \fIframework\fR.
 If omitted, \fIdylib\fR is assumed.
@@ -113,7 +113,8 @@ Print version info and exit.
 Use verbose output.
 .TP
 \fB\-\-extern\fR \fINAME\fR=\fIPATH\fR
-Specify where an external rust library is located.
+Specify where an external rust library is located. These should match
+\fIextern\fR declarations in the crate's source code.
 .TP
 \fB\-\-sysroot\fR \fIPATH\fR
 Override the system root.
diff --git a/src/doc/reference.md b/src/doc/reference.md
index 4d5564d9faf..b4dec8f1fef 100644
--- a/src/doc/reference.md
+++ b/src/doc/reference.md
@@ -2059,6 +2059,11 @@ The following configurations must be defined by the implementation:
   `"mips"`, `"powerpc"`, `"arm"`, or `"aarch64"`.
 * `target_endian = "..."`. Endianness of the target CPU, either `"little"` or
   `"big"`.
+* `target_env = ".."` - an option provided by the compiler by default
+  describing the runtime environment of the target platform. Some examples of
+  this are `musl` for builds targeting the MUSL libc implementation, `msvc` for
+  Windows builds targeting MSVC, and `gnu` frequently the rest of the time. This
+  option may also be blank on some platforms.
 * `target_family = "..."`. Operating system family of the target, e. g.
   `"unix"` or `"windows"`. The value of this configuration option is defined
   as a configuration itself, like `unix` or `windows`.
diff --git a/src/doc/trpl/functions.md b/src/doc/trpl/functions.md
index 5b29965efc6..84cea5dabc3 100644
--- a/src/doc/trpl/functions.md
+++ b/src/doc/trpl/functions.md
@@ -214,11 +214,61 @@ fn diverges() -> ! {
 
 `panic!` is a macro, similar to `println!()` that we’ve already seen. Unlike
 `println!()`, `panic!()` causes the current thread of execution to crash with
-the given message.
+the given message. Because this function will cause a crash, it will never
+return, and so it has the type ‘`!`’, which is read ‘diverges’.
 
-Because this function will cause a crash, it will never return, and so it has
-the type ‘`!`’, which is read ‘diverges’. A diverging function can be used
-as any type:
+If you add a main function that calls `diverges()` and run it, you’ll get
+some output that looks like this:
+
+```text
+thread ‘<main>’ panicked at ‘This function never returns!’, hello.rs:2
+```
+
+If you want more information, you can get a backtrace by setting the
+`RUST_BACKTRACE` environment variable:
+
+```text
+$ RUST_BACKTRACE=1 ./diverges
+thread '<main>' panicked at 'This function never returns!', hello.rs:2
+stack backtrace:
+   1:     0x7f402773a829 - sys::backtrace::write::h0942de78b6c02817K8r
+   2:     0x7f402773d7fc - panicking::on_panic::h3f23f9d0b5f4c91bu9w
+   3:     0x7f402773960e - rt::unwind::begin_unwind_inner::h2844b8c5e81e79558Bw
+   4:     0x7f4027738893 - rt::unwind::begin_unwind::h4375279447423903650
+   5:     0x7f4027738809 - diverges::h2266b4c4b850236beaa
+   6:     0x7f40277389e5 - main::h19bb1149c2f00ecfBaa
+   7:     0x7f402773f514 - rt::unwind::try::try_fn::h13186883479104382231
+   8:     0x7f402773d1d8 - __rust_try
+   9:     0x7f402773f201 - rt::lang_start::ha172a3ce74bb453aK5w
+  10:     0x7f4027738a19 - main
+  11:     0x7f402694ab44 - __libc_start_main
+  12:     0x7f40277386c8 - <unknown>
+  13:                0x0 - <unknown>
+```
+
+`RUST_BACKTRACE` also works with Cargo’s `run` command:
+
+```text
+$ RUST_BACKTRACE=1 cargo run
+     Running `target/debug/diverges`
+thread '<main>' panicked at 'This function never returns!', hello.rs:2
+stack backtrace:
+   1:     0x7f402773a829 - sys::backtrace::write::h0942de78b6c02817K8r
+   2:     0x7f402773d7fc - panicking::on_panic::h3f23f9d0b5f4c91bu9w
+   3:     0x7f402773960e - rt::unwind::begin_unwind_inner::h2844b8c5e81e79558Bw
+   4:     0x7f4027738893 - rt::unwind::begin_unwind::h4375279447423903650
+   5:     0x7f4027738809 - diverges::h2266b4c4b850236beaa
+   6:     0x7f40277389e5 - main::h19bb1149c2f00ecfBaa
+   7:     0x7f402773f514 - rt::unwind::try::try_fn::h13186883479104382231
+   8:     0x7f402773d1d8 - __rust_try
+   9:     0x7f402773f201 - rt::lang_start::ha172a3ce74bb453aK5w
+  10:     0x7f4027738a19 - main
+  11:     0x7f402694ab44 - __libc_start_main
+  12:     0x7f40277386c8 - <unknown>
+  13:                0x0 - <unknown>
+```
+
+A diverging function can be used as any type:
 
 ```should_panic
 # fn diverges() -> ! {
diff --git a/src/libcollections/binary_heap.rs b/src/libcollections/binary_heap.rs
index b817ed6a6d0..bedeab67420 100644
--- a/src/libcollections/binary_heap.rs
+++ b/src/libcollections/binary_heap.rs
@@ -112,7 +112,7 @@
 //!     //                  7
 //!     //          +-----------------+
 //!     //          |                 |
-//!     //          v   1        2    |
+//!     //          v   1        2    |  2
 //!     //          0 -----> 1 -----> 3 ---> 4
 //!     //          |        ^        ^      ^
 //!     //          |        | 1      |      |