syntax_ext: Improve and simplify code generated by `#[global_allocator]`

Instead of
```
mod allocator_abi { /* methods */ }
```
we now generate
```
const _: () = { /* methods */ }
```
and use `std_path` for paths referring to standard library entities.

This way we no longer need to generate `use` and `extern crate` imports, and `#[global_allocator]` starts working inside unnamed blocks.

2 files changed, 6 insertions, 4 deletions

diff --git a/src/test/run-pass/allocator/custom-in-block.rs b/src/test/run-pass/allocator/custom-in-block.rs
index 506154ec601..12813a1fc8b 100644
--- a/src/test/run-pass/allocator/custom-in-block.rs
+++ b/src/test/run-pass/allocator/custom-in-block.rs
@@ -13,9 +13,10 @@ fn main() {
     #[global_allocator]
     pub static GLOBAL: A = A(AtomicUsize::new(0));
 
+    let n = GLOBAL.0.load(Ordering::SeqCst);
     let s = Box::new(0);
     helper::work_with(&s);
-    assert_eq!(GLOBAL.0.load(Ordering::SeqCst), 1);
+    assert_eq!(GLOBAL.0.load(Ordering::SeqCst), n + 1);
     drop(s);
-    assert_eq!(GLOBAL.0.load(Ordering::SeqCst), 2);
+    assert_eq!(GLOBAL.0.load(Ordering::SeqCst), n + 2);
 }
diff --git a/src/test/run-pass/allocator/custom-in-submodule.rs b/src/test/run-pass/allocator/custom-in-submodule.rs
index f9c4ad7668b..ea341b1ac14 100644
--- a/src/test/run-pass/allocator/custom-in-submodule.rs
+++ b/src/test/run-pass/allocator/custom-in-submodule.rs
@@ -17,9 +17,10 @@ mod submodule {
 }
 
 fn main() {
+    let n = submodule::GLOBAL.0.load(Ordering::SeqCst);
     let s = Box::new(0);
     helper::work_with(&s);
-    assert_eq!(submodule::GLOBAL.0.load(Ordering::SeqCst), 1);
+    assert_eq!(submodule::GLOBAL.0.load(Ordering::SeqCst), n + 1);
     drop(s);
-    assert_eq!(submodule::GLOBAL.0.load(Ordering::SeqCst), 2);
+    assert_eq!(submodule::GLOBAL.0.load(Ordering::SeqCst), n + 2);
 }