Auto merge of #41349 - eddyb:ty-contents, r=nikomatsakis

rustc: replace TypeContents with two independent properties (is_freeze / needs_drop).

`InteriorUnsafe` / `interior_unsafe` was replaced with a private lang-item `Freeze` auto trait in libcore.

`OwnsDtor` / `needs_drop` was replaced with a specialized traversal that *doesn't* avoid caching results in case of a cycle, as the only cycles left can only occur in erroneous "types with infinite sizes", references and raw pointers not having destructors. Also, `Copy` is now checked at every step of the recursion.

r? @nikomatsakis

Author: bors

src/bootstrap/compile.rs

@@ -151,6 +151,7 @@ pub fn build_startup_objects(build: &Build, for_compiler: &Compiler, target: &st
         if !up_to_date(src_file, dst_file) {
             let mut cmd = Command::new(&compiler_path);
             build.run(cmd.env("RUSTC_BOOTSTRAP", "1")
+                        .arg("--cfg").arg(format!("stage{}", compiler.stage))
                         .arg("--target").arg(target)
                         .arg("--emit=obj")
                         .arg("--out-dir").arg(dst_dir)

src/libcore/marker.rs

@@ -16,6 +16,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use cell::UnsafeCell;
 use cmp;
 use hash::Hash;
 use hash::Hasher;
@@ -553,3 +554,19 @@ mod impls {
     #[stable(feature = "rust1", since = "1.0.0")]
     unsafe impl<'a, T: Send + ?Sized> Send for &'a mut T {}
 }
+
+/// Compiler-internal trait used to determine whether a type contains
+/// any `UnsafeCell` internally, but not through an indirection.
+/// This affects, for example, whether a `static` of that type is
+/// placed in read-only static memory or writable static memory.
+#[cfg_attr(not(stage0), lang = "freeze")]
+unsafe trait Freeze {}
+
+unsafe impl Freeze for .. {}
+
+impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
+unsafe impl<T: ?Sized> Freeze for PhantomData<T> {}
+unsafe impl<T: ?Sized> Freeze for *const T {}
+unsafe impl<T: ?Sized> Freeze for *mut T {}
+unsafe impl<'a, T: ?Sized> Freeze for &'a T {}
+unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}

src/librustc/middle/lang_items.rs

@@ -274,6 +274,7 @@ language_item_table! {
     UnsizeTraitLangItem,             "unsize",                  unsize_trait;
     CopyTraitLangItem,               "copy",                    copy_trait;
     SyncTraitLangItem,               "sync",                    sync_trait;
+    FreezeTraitLangItem,             "freeze",                  freeze_trait;
 
     DropTraitLangItem,               "drop",                    drop_trait;
 

src/librustc/ty/contents.rs

@@ -436,9 +436,6 @@ pub struct GlobalCtxt<'tcx> {
     // Internal cache for metadata decoding. No need to track deps on this.
     pub rcache: RefCell<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
 
-    // Cache for the type-contents routine. FIXME -- track deps?
-    pub tc_cache: RefCell<FxHashMap<Ty<'tcx>, ty::contents::TypeContents>>,
-
     // FIXME dep tracking -- should be harmless enough
     pub normalized_cache: RefCell<FxHashMap<Ty<'tcx>, Ty<'tcx>>>,
 
@@ -708,7 +705,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             freevars: RefCell::new(resolutions.freevars),
             maybe_unused_trait_imports: resolutions.maybe_unused_trait_imports,
             rcache: RefCell::new(FxHashMap()),
-            tc_cache: RefCell::new(FxHashMap()),
             normalized_cache: RefCell::new(FxHashMap()),
             inhabitedness_cache: RefCell::new(FxHashMap()),
             lang_items: lang_items,