rustc: Add knowledge of Windows subsystems.

This commit is an implementation of [RFC 1665] which adds support for the
`#![windows_subsystem]` attribute. This attribute allows specifying either the
"windows" or "console" subsystems on Windows to the linker.

[RFC 1665]: https://github.com/rust-lang/rfcs/blob/master/text/1665-windows-subsystem.md

Previously all Rust executables were compiled as the "console" subsystem which
meant that if you wanted a graphical application it would erroneously pop up a
console whenever opened. When compiling an application, however, this is
undesired behavior and the "windows" subsystem is used instead to have control
over user interactions.

This attribute is validated, but ignored on all non-Windows platforms.

cc #37499

1 files changed, 9 insertions, 0 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 129e4a82338..bf6482e5b99 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -309,6 +309,9 @@ declare_features! (
 
     // Allows field shorthands (`x` meaning `x: x`) in struct literal expressions.
     (active, field_init_shorthand, "1.14.0", Some(37340)),
+
+    // The #![windows_subsystem] attribute
+    (active, windows_subsystem, "1.14.0", Some(37499)),
 );
 
 declare_features! (
@@ -713,6 +716,12 @@ pub const KNOWN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeGat
                                               "defining reflective traits is still evolving",
                                               cfg_fn!(reflect))),
 
+    ("windows_subsystem", Whitelisted, Gated(Stability::Unstable,
+                                             "windows_subsystem",
+                                             "the windows subsystem attribute \
+                                              id currently unstable",
+                                             cfg_fn!(windows_subsystem))),
+
     // Crate level attributes
     ("crate_name", CrateLevel, Ungated),
     ("crate_type", CrateLevel, Ungated),