Merge pull request rust-lang#100 from oli-obk/tuple_struct_constructor_as_fn

allow the use of tuple struct constructors as functions

Author: solson

src/error.rs

@@ -52,6 +52,7 @@ pub enum EvalError<'tcx> {
     ReallocatedFrozenMemory,
     DeallocatedFrozenMemory,
     Layout(layout::LayoutError<'tcx>),
+    Unreachable,
 }
 
 pub type EvalResult<'tcx, T> = Result<T, EvalError<'tcx>>;
@@ -122,6 +123,8 @@ impl<'tcx> Error for EvalError<'tcx> {
                 "rustc layout computation failed",
             EvalError::UnterminatedCString(_) =>
                 "attempted to get length of a null terminated string, but no null found before end of allocation",
+            EvalError::Unreachable =>
+                "entered unreachable code",
         }
     }
 

src/eval_context.rs

@@ -10,6 +10,7 @@ use rustc::ty::layout::{self, Layout, Size};
 use rustc::ty::subst::{self, Subst, Substs};
 use rustc::ty::{self, Ty, TyCtxt, TypeFoldable};
 use rustc_data_structures::indexed_vec::Idx;
+use rustc_data_structures::fx::FxHashSet;
 use syntax::codemap::{self, DUMMY_SP};
 
 use error::{EvalError, EvalResult};
@@ -1468,3 +1469,7 @@ pub fn monomorphize_field_ty<'a, 'tcx:'a >(tcx: TyCtxt<'a, 'tcx, 'tcx>, f: &ty::
     let substituted = &f.ty(tcx, substs);
     tcx.normalize_associated_type(&substituted)
 }
+
+pub fn is_inhabited<'a, 'tcx: 'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>, ty: Ty<'tcx>) -> bool {
+    ty.uninhabited_from(&mut FxHashSet::default(), tcx).is_empty()
+}

src/terminator/mod.rs

@@ -9,7 +9,7 @@ use syntax::codemap::{DUMMY_SP, Span};
 use syntax::{ast, attr};
 
 use error::{EvalError, EvalResult};
-use eval_context::{EvalContext, IntegerExt, StackPopCleanup, monomorphize_field_ty};
+use eval_context::{EvalContext, IntegerExt, StackPopCleanup, monomorphize_field_ty, is_inhabited};
 use lvalue::{Lvalue, LvalueExtra};
 use memory::Pointer;
 use value::PrimVal;
@@ -155,7 +155,7 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
 
             DropAndReplace { .. } => unimplemented!(),
             Resume => unimplemented!(),
-            Unreachable => unimplemented!(),
+            Unreachable => return Err(EvalError::Unreachable),
         }
 
         Ok(())
@@ -200,7 +200,10 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
             Abi::RustIntrinsic => {
                 let ty = fn_ty.sig.0.output();
                 let layout = self.type_layout(ty)?;
-                let (ret, target) = destination.unwrap();
+                let (ret, target) = match destination {
+                    Some(dest) if is_inhabited(self.tcx, ty) => dest,
+                    _ => return Err(EvalError::Unreachable),
+                };
                 self.call_intrinsic(def_id, substs, arg_operands, ret, ty, layout, target)?;
                 Ok(())
             }
@@ -229,6 +232,33 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
                         (def_id, substs, Vec::new())
                     };
 
+                // FIXME(eddyb) Detect ADT constructors more efficiently.
+                if let Some(adt_def) = fn_ty.sig.skip_binder().output().ty_adt_def() {
+                    if let Some(v) = adt_def.variants.iter().find(|v| resolved_def_id == v.did) {
+                        let (lvalue, target) = destination.expect("tuple struct constructors can't diverge");
+                        let dest_ty = self.tcx.item_type(adt_def.did);
+                        let dest_layout = self.type_layout(dest_ty)?;
+                        match *dest_layout {
+                            Layout::Univariant { ref variant, .. } => {
+                                assert_eq!(v.disr_val.to_u128_unchecked(), 0);
+                                let offsets = variant.offsets.iter().map(|s| s.bytes());
+
+                                // FIXME: don't allocate for single or dual field structs
+                                let dest = self.force_allocation(lvalue)?.to_ptr();
+
+                                for (offset, (value, value_ty)) in offsets.into_iter().zip(args) {
+                                    let field_dest = dest.offset(offset);
+                                    self.write_value_to_ptr(value, field_dest, value_ty)?;
+                                }
+                            },
+                            // FIXME: enum variant constructors
+                            _ => bug!("bad layout for tuple struct constructor: {:?}", dest_layout),
+                        }
+                        self.goto_block(target);
+                        return Ok(());
+                    }
+                }
+
                 let mir = self.load_mir(resolved_def_id)?;
                 let (return_lvalue, return_to_block) = match destination {
                     Some((lvalue, block)) => (lvalue, StackPopCleanup::Goto(block)),

tests/compile-fail/never_say_never.rs

@@ -0,0 +1,12 @@
+#![feature(never_type)]
+#![allow(unreachable_code)]
+
+fn main() {
+    let y = &5;
+    let x: ! = unsafe {
+        *(y as *const _ as *const !) //~ ERROR entered unreachable code
+    };
+    f(x)
+}
+
+fn f(x: !) -> ! { x }

tests/compile-fail/never_transmute_humans.rs

@@ -0,0 +1,14 @@
+#![feature(never_type)]
+#![allow(unreachable_code)]
+#![allow(unused_variables)]
+
+struct Human;
+
+fn main() {
+    let x: ! = unsafe {
+        std::mem::transmute::<Human, !>(Human) //~ ERROR entered unreachable code
+    };
+    f(x)
+}
+
+fn f(x: !) -> ! { x }

tests/compile-fail/never_transmute_void.rs

@@ -0,0 +1,16 @@
+#![feature(never_type)]
+#![allow(unreachable_code)]
+#![allow(unused_variables)]
+
+enum Void {}
+
+fn f(v: Void) -> ! {
+    match v {}
+}
+
+fn main() {
+    let v: Void = unsafe {
+        std::mem::transmute::<(), Void>(()) //~ ERROR entered unreachable code
+    };
+    f(v);
+}

tests/run-pass/tuple_like_struct_constructor.rs

@@ -0,0 +1,5 @@
+fn main() {
+    #[derive(PartialEq, Eq, Debug)]
+    struct A(i32);
+    assert_eq!(Some(42).map(A), Some(A(42)));
+}