Auto merge of #46115 - alexcrichton:add-wasm-target, r=kennytm

rustbuild: Enable WebAssembly backend by default

This commit alters how we compile LLVM by default enabling the WebAssembly
backend. This then also adds the wasm32-unknown-unknown target to get compiled
on the `cross` builder and distributed through rustup. Tests are not yet enabled
for this target but that should hopefully be coming soon!

2 files changed, 111 insertions, 76 deletions

diff --git a/src/libstd/os/mod.rs b/src/libstd/os/mod.rs
index 122f15d1d4c..ac7809451d1 100644
--- a/src/libstd/os/mod.rs
+++ b/src/libstd/os/mod.rs
@@ -13,35 +13,53 @@
 #![stable(feature = "os", since = "1.0.0")]
 #![allow(missing_docs, bad_style, missing_debug_implementations)]
 
-#[cfg(all(not(dox), any(target_os = "redox", unix)))]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use sys::ext as unix;
-#[cfg(all(not(dox), windows))]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use sys::ext as windows;
-
-#[cfg(dox)]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use sys::unix_ext as unix;
-#[cfg(dox)]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use sys::windows_ext as windows;
-
-#[cfg(any(dox, target_os = "linux", target_os = "l4re"))]
-#[doc(cfg(target_os = "linux"))]
-pub mod linux;
-
-#[cfg(all(not(dox), target_os = "android"))]    pub mod android;
-#[cfg(all(not(dox), target_os = "bitrig"))]     pub mod bitrig;
-#[cfg(all(not(dox), target_os = "dragonfly"))]  pub mod dragonfly;
-#[cfg(all(not(dox), target_os = "freebsd"))]    pub mod freebsd;
-#[cfg(all(not(dox), target_os = "haiku"))]      pub mod haiku;
-#[cfg(all(not(dox), target_os = "ios"))]        pub mod ios;
-#[cfg(all(not(dox), target_os = "macos"))]      pub mod macos;
-#[cfg(all(not(dox), target_os = "netbsd"))]     pub mod netbsd;
-#[cfg(all(not(dox), target_os = "openbsd"))]    pub mod openbsd;
-#[cfg(all(not(dox), target_os = "solaris"))]    pub mod solaris;
-#[cfg(all(not(dox), target_os = "emscripten"))] pub mod emscripten;
-#[cfg(all(not(dox), target_os = "fuchsia"))]    pub mod fuchsia;
+cfg_if! {
+    if #[cfg(dox)] {
+
+        // When documenting libstd we want to show unix/windows/linux modules as
+        // these are the "main modules" that are used across platforms. This
+        // should help show platform-specific functionality in a hopefully
+        // cross-platform way in the documentation
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        pub use sys::unix_ext as unix;
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        pub use sys::windows_ext as windows;
+
+        #[doc(cfg(target_os = "linux"))]
+        pub mod linux;
+
+    } else {
+
+        // If we're not documenting libstd then we just expose everything as we
+        // otherwise would.
+
+        #[cfg(target_os = "android")]    pub mod android;
+        #[cfg(target_os = "bitrig")]     pub mod bitrig;
+        #[cfg(target_os = "dragonfly")]  pub mod dragonfly;
+        #[cfg(target_os = "freebsd")]    pub mod freebsd;
+        #[cfg(target_os = "haiku")]      pub mod haiku;
+        #[cfg(target_os = "ios")]        pub mod ios;
+        #[cfg(target_os = "macos")]      pub mod macos;
+        #[cfg(target_os = "netbsd")]     pub mod netbsd;
+        #[cfg(target_os = "openbsd")]    pub mod openbsd;
+        #[cfg(target_os = "solaris")]    pub mod solaris;
+        #[cfg(target_os = "emscripten")] pub mod emscripten;
+        #[cfg(target_os = "fuchsia")]    pub mod fuchsia;
+
+        #[cfg(any(target_os = "redox", unix))]
+        #[stable(feature = "rust1", since = "1.0.0")]
+        pub use sys::ext as unix;
+
+        #[cfg(windows)]
+        #[stable(feature = "rust1", since = "1.0.0")]
+        pub use sys::ext as windows;
+
+        #[cfg(any(target_os = "linux", target_os = "l4re"))]
+        pub mod linux;
+
+    }
+}
 
 pub mod raw;
diff --git a/src/libstd/sys/mod.rs b/src/libstd/sys/mod.rs
index 27d6433b329..be8cb88416b 100644
--- a/src/libstd/sys/mod.rs
+++ b/src/libstd/sys/mod.rs
@@ -32,49 +32,66 @@
 
 #![allow(missing_debug_implementations)]
 
-pub use self::imp::*;
-
-#[cfg(unix)]
-#[path = "unix/mod.rs"]
-mod imp;
-
-#[cfg(windows)]
-#[path = "windows/mod.rs"]
-mod imp;
-
-#[cfg(target_os = "redox")]
-#[path = "redox/mod.rs"]
-mod imp;
-
-#[cfg(all(target_arch = "wasm32", not(target_os = "emscripten")))]
-#[path = "wasm/mod.rs"]
-mod imp;
-
-// Import essential modules from both platforms when documenting.
-
-#[cfg(all(dox, not(unix)))]
-use os::linux as platform;
-
-#[cfg(all(dox, not(any(unix, target_os = "redox"))))]
-#[path = "unix/ext/mod.rs"]
-pub mod unix_ext;
-
-#[cfg(all(dox, any(unix, target_os = "redox")))]
-pub use self::ext as unix_ext;
-
-
-#[cfg(all(dox, not(windows)))]
-#[macro_use]
-#[path = "windows/compat.rs"]
-mod compat;
-
-#[cfg(all(dox, not(windows)))]
-#[path = "windows/c.rs"]
-mod c;
-
-#[cfg(all(dox, not(windows)))]
-#[path = "windows/ext/mod.rs"]
-pub mod windows_ext;
-
-#[cfg(all(dox, windows))]
-pub use self::ext as windows_ext;
+cfg_if! {
+    if #[cfg(unix)] {
+        mod unix;
+        pub use self::unix::*;
+    } else if #[cfg(windows)] {
+        mod windows;
+        pub use self::windows::*;
+    } else if #[cfg(target_os = "redox")] {
+        mod redox;
+        pub use self::redox::*;
+    } else if #[cfg(target_arch = "wasm32")] {
+        mod wasm;
+        pub use self::wasm::*;
+    } else {
+        compile_error!("libstd doesn't compile for this platform yet");
+    }
+}
+
+// Import essential modules from both platforms when documenting. These are
+// then later used in the `std::os` module when documenting, for example,
+// Windows when we're compiling for Linux.
+
+#[cfg(dox)]
+cfg_if! {
+    if #[cfg(any(unix, target_os = "redox"))] {
+        // On unix we'll document what's already available
+        pub use self::ext as unix_ext;
+    } else if #[cfg(target_arch = "wasm32")] {
+        // On wasm right now the module below doesn't compile (missing things
+        // in `libc` which is empty) so just omit everything with an empty module
+        #[unstable(issue = "0", feature = "std_internals")]
+        pub mod unix_ext {}
+    } else {
+        // On other platforms like Windows document the bare bones of unix
+        use os::linux as platform;
+        #[path = "unix/ext/mod.rs"]
+        pub mod unix_ext;
+    }
+}
+
+#[cfg(dox)]
+cfg_if! {
+    if #[cfg(windows)] {
+        // On windows we'll just be documenting what's already available
+        pub use self::ext as windows_ext;
+    } else if #[cfg(target_arch = "wasm32")] {
+        // On wasm right now the shim below doesn't compile, so just omit it
+        #[unstable(issue = "0", feature = "std_internals")]
+        pub mod windows_ext {}
+    } else {
+        // On all other platforms (aka linux/osx/etc) then pull in a "minimal"
+        // amount of windows goop which ends up compiling
+        #[macro_use]
+        #[path = "windows/compat.rs"]
+        mod compat;
+
+        #[path = "windows/c.rs"]
+        mod c;
+
+        #[path = "windows/ext/mod.rs"]
+        pub mod windows_ext;
+    }
+}