Rollup merge of #61720 - alexcrichton:libstd-cfg-if-dep, r=sfackler

std: Remove internal definitions of `cfg_if!` macro

This is duplicated in a few locations throughout the sysroot to work
around issues with not exporting a macro in libstd but still wanting it
available to sysroot crates to define blocks. Nowadays though we can
simply depend on the `cfg-if` crate on crates.io, allowing us to use it
from there!

8 files changed, 14 insertions, 43 deletions

diff --git a/src/libstd/Cargo.toml b/src/libstd/Cargo.toml
index 30e23f1007f..a170dae2b08 100644
--- a/src/libstd/Cargo.toml
+++ b/src/libstd/Cargo.toml
@@ -15,6 +15,7 @@ crate-type = ["dylib", "rlib"]
 
 [dependencies]
 alloc = { path = "../liballoc" }
+cfg-if = "0.1.8"
 panic_unwind = { path = "../libpanic_unwind", optional = true }
 panic_abort = { path = "../libpanic_abort" }
 core = { path = "../libcore" }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index a3356e6be2c..e0ffc9ba92f 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -336,6 +336,12 @@ extern crate libc;
 #[allow(unused_extern_crates)]
 extern crate unwind;
 
+// Only needed for now for the `std_detect` module until that crate changes to
+// use `cfg_if::cfg_if!`
+#[macro_use]
+#[cfg(not(test))]
+extern crate cfg_if;
+
 // During testing, this crate is not actually the "real" std library, but rather
 // it links to the real std library, which was compiled from this same source
 // code. So any lang items std defines are conditionally excluded (or else they
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index ef1b549d1dc..d695141bef0 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -896,39 +896,3 @@ mod builtin {
         ($cond:expr, $($arg:tt)+) => ({ /* compiler built-in */ });
     }
 }
-
-/// Defines `#[cfg]` if-else statements.
-///
-/// This is similar to the `if/elif` C preprocessor macro by allowing definition
-/// of a cascade of `#[cfg]` cases, emitting the implementation which matches
-/// first.
-///
-/// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code
-/// without having to rewrite each clause multiple times.
-macro_rules! cfg_if {
-    ($(
-        if #[cfg($($meta:meta),*)] { $($it:item)* }
-    ) else * else {
-        $($it2:item)*
-    }) => {
-        __cfg_if_items! {
-            () ;
-            $( ( ($($meta),*) ($($it)*) ), )*
-            ( () ($($it2)*) ),
-        }
-    }
-}
-
-macro_rules! __cfg_if_items {
-    (($($not:meta,)*) ; ) => {};
-    (($($not:meta,)*) ; ( ($($m:meta),*) ($($it:item)*) ), $($rest:tt)*) => {
-        __cfg_if_apply! { cfg(all(not(any($($not),*)), $($m,)*)), $($it)* }
-        __cfg_if_items! { ($($not,)* $($m,)*) ; $($rest)* }
-    }
-}
-
-macro_rules! __cfg_if_apply {
-    ($m:meta, $($it:item)*) => {
-        $(#[$m] $it)*
-    }
-}
diff --git a/src/libstd/os/mod.rs b/src/libstd/os/mod.rs
index 44cbc180b8b..94e8b7805cf 100644
--- a/src/libstd/os/mod.rs
+++ b/src/libstd/os/mod.rs
@@ -3,7 +3,7 @@
 #![stable(feature = "os", since = "1.0.0")]
 #![allow(missing_docs, nonstandard_style, missing_debug_implementations)]
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(rustdoc)] {
 
         // When documenting libstd we want to show unix/windows/linux modules as
diff --git a/src/libstd/sys/mod.rs b/src/libstd/sys/mod.rs
index 3f3cedc53b7..21360e2e0f0 100644
--- a/src/libstd/sys/mod.rs
+++ b/src/libstd/sys/mod.rs
@@ -22,7 +22,7 @@
 
 #![allow(missing_debug_implementations)]
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(unix)] {
         mod unix;
         pub use self::unix::*;
@@ -54,7 +54,7 @@ cfg_if! {
 // Windows when we're compiling for Linux.
 
 #[cfg(rustdoc)]
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(any(unix, target_os = "redox"))] {
         // On unix we'll document what's already available
         #[stable(feature = "rust1", since = "1.0.0")]
@@ -77,7 +77,7 @@ cfg_if! {
 }
 
 #[cfg(rustdoc)]
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(windows)] {
         // On windows we'll just be documenting what's already available
         #[allow(missing_docs)]
diff --git a/src/libstd/sys/wasm/mod.rs b/src/libstd/sys/wasm/mod.rs
index 9ea8bd16538..7d157709eb6 100644
--- a/src/libstd/sys/wasm/mod.rs
+++ b/src/libstd/sys/wasm/mod.rs
@@ -40,7 +40,7 @@ pub mod stdio;
 
 pub use crate::sys_common::os_str_bytes as os_str;
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(target_feature = "atomics")] {
         #[path = "condvar_atomics.rs"]
         pub mod condvar;
diff --git a/src/libstd/sys/wasm/thread.rs b/src/libstd/sys/wasm/thread.rs
index 1dc786cd5d7..61b4003cd3d 100644
--- a/src/libstd/sys/wasm/thread.rs
+++ b/src/libstd/sys/wasm/thread.rs
@@ -59,7 +59,7 @@ pub mod guard {
     pub unsafe fn init() -> Option<Guard> { None }
 }
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(all(target_feature = "atomics", feature = "wasm-bindgen-threads"))] {
         #[link(wasm_import_module = "__wbindgen_thread_xform__")]
         extern {
diff --git a/src/libstd/sys_common/mod.rs b/src/libstd/sys_common/mod.rs
index c4daedefd8e..13a59f66c5c 100644
--- a/src/libstd/sys_common/mod.rs
+++ b/src/libstd/sys_common/mod.rs
@@ -65,7 +65,7 @@ pub mod bytestring;
 pub mod process;
 pub mod fs;
 
-cfg_if! {
+cfg_if::cfg_if! {
     if #[cfg(any(target_os = "cloudabi",
                  target_os = "l4re",
                  target_os = "redox",