Rollup merge of #53076 - QuietMisdreavus:cfg-rustdoc, r=GuillaumeGomez

set cfg(rustdoc) when rustdoc is running on a crate

When using `#[doc(cfg)]` to document platform-specific items, it's a little cumbersome to get all the platforms' items to appear all at once. For example, the standard library adds `--cfg dox` to rustdoc's command line whenever it builds docs, and the documentation for `#![feature(doc_cfg)]` suggests using a Cargo feature to approximate the same thing. This is a little awkward, because you always need to remember to set `--features dox` whenever you build documentation.

This PR proposes making rustdoc set `#[cfg(rustdoc)]` whenever it runs on a crate, to provide an officially-sanctioned version of this that is set automatically. This way, there's a standardized way to declare that a certain version of an item is specifically when building docs.

To try to prevent the spread of this feature from happening too quickly, this PR also restricts the use of this flag to whenever `#![feature(doc_cfg)]` is active. I'm sure there are other uses for this, but right now i'm tying it to this feature. (If it makes more sense to give this its own feature, i can easily do that.)

3 files changed, 19 insertions, 19 deletions

diff --git a/src/libstd/sys/mod.rs b/src/libstd/sys/mod.rs
index c44db3b1072..61e4ce66eec 100644
--- a/src/libstd/sys/mod.rs
+++ b/src/libstd/sys/mod.rs
@@ -57,7 +57,7 @@ cfg_if! {
 // then later used in the `std::os` module when documenting, for example,
 // Windows when we're compiling for Linux.
 
-#[cfg(dox)]
+#[cfg(rustdoc)]
 cfg_if! {
     if #[cfg(any(unix, target_os = "redox"))] {
         // On unix we'll document what's already available
@@ -77,7 +77,7 @@ cfg_if! {
     }
 }
 
-#[cfg(dox)]
+#[cfg(rustdoc)]
 cfg_if! {
     if #[cfg(windows)] {
         // On windows we'll just be documenting what's already available
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index 2b9fbc9ef39..17214be5b05 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -13,22 +13,22 @@
 use io::{self, ErrorKind};
 use libc;
 
-#[cfg(any(dox, target_os = "linux"))] pub use os::linux as platform;
-
-#[cfg(all(not(dox), target_os = "android"))]   pub use os::android as platform;
-#[cfg(all(not(dox), target_os = "bitrig"))]    pub use os::bitrig as platform;
-#[cfg(all(not(dox), target_os = "dragonfly"))] pub use os::dragonfly as platform;
-#[cfg(all(not(dox), target_os = "freebsd"))]   pub use os::freebsd as platform;
-#[cfg(all(not(dox), target_os = "haiku"))]     pub use os::haiku as platform;
-#[cfg(all(not(dox), target_os = "ios"))]       pub use os::ios as platform;
-#[cfg(all(not(dox), target_os = "macos"))]     pub use os::macos as platform;
-#[cfg(all(not(dox), target_os = "netbsd"))]    pub use os::netbsd as platform;
-#[cfg(all(not(dox), target_os = "openbsd"))]   pub use os::openbsd as platform;
-#[cfg(all(not(dox), target_os = "solaris"))]   pub use os::solaris as platform;
-#[cfg(all(not(dox), target_os = "emscripten"))] pub use os::emscripten as platform;
-#[cfg(all(not(dox), target_os = "fuchsia"))]   pub use os::fuchsia as platform;
-#[cfg(all(not(dox), target_os = "l4re"))]      pub use os::linux as platform;
-#[cfg(all(not(dox), target_os = "hermit"))]    pub use os::hermit as platform;
+#[cfg(any(rustdoc, target_os = "linux"))] pub use os::linux as platform;
+
+#[cfg(all(not(rustdoc), target_os = "android"))]   pub use os::android as platform;
+#[cfg(all(not(rustdoc), target_os = "bitrig"))]    pub use os::bitrig as platform;
+#[cfg(all(not(rustdoc), target_os = "dragonfly"))] pub use os::dragonfly as platform;
+#[cfg(all(not(rustdoc), target_os = "freebsd"))]   pub use os::freebsd as platform;
+#[cfg(all(not(rustdoc), target_os = "haiku"))]     pub use os::haiku as platform;
+#[cfg(all(not(rustdoc), target_os = "ios"))]       pub use os::ios as platform;
+#[cfg(all(not(rustdoc), target_os = "macos"))]     pub use os::macos as platform;
+#[cfg(all(not(rustdoc), target_os = "netbsd"))]    pub use os::netbsd as platform;
+#[cfg(all(not(rustdoc), target_os = "openbsd"))]   pub use os::openbsd as platform;
+#[cfg(all(not(rustdoc), target_os = "solaris"))]   pub use os::solaris as platform;
+#[cfg(all(not(rustdoc), target_os = "emscripten"))] pub use os::emscripten as platform;
+#[cfg(all(not(rustdoc), target_os = "fuchsia"))]   pub use os::fuchsia as platform;
+#[cfg(all(not(rustdoc), target_os = "l4re"))]      pub use os::linux as platform;
+#[cfg(all(not(rustdoc), target_os = "hermit"))]    pub use os::hermit as platform;
 
 pub use self::rand::hashmap_random_keys;
 pub use libc::strlen;
diff --git a/src/libstd/sys/windows/c.rs b/src/libstd/sys/windows/c.rs
index 8a744519e91..4c64322a6dc 100644
--- a/src/libstd/sys/windows/c.rs
+++ b/src/libstd/sys/windows/c.rs
@@ -794,7 +794,7 @@ pub struct FLOATING_SAVE_AREA {
 // will not appear in the final documentation. This should be also defined for
 // other architectures supported by Windows such as ARM, and for historical
 // interest, maybe MIPS and PowerPC as well.
-#[cfg(all(dox, not(any(target_arch = "x86_64", target_arch = "x86", target_arch = "aarch64"))))]
+#[cfg(all(rustdoc, not(any(target_arch = "x86_64", target_arch = "x86", target_arch = "aarch64"))))]
 pub enum CONTEXT {}
 
 #[cfg(target_arch = "aarch64")]