Rollup merge of rust-lang#40025 - est31:master, r=eddyb

Implement non-capturing closure to fn coercion

Implements non capturing closure coercion ([RFC 1558](https://github.com/rust-lang/rfcs/blob/master/text/1558-closure-to-fn-coercion.md)).

cc tracking issue rust-lang#39817

src/librustc/middle/expr_use_visitor.rs

@@ -715,6 +715,7 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
  adjustment::Adjust::NeverToAny |
  adjustment::Adjust::ReifyFnPointer |
  adjustment::Adjust::UnsafeFnPointer |
+ adjustment::Adjust::ClosureFnPointer |
  adjustment::Adjust::MutToConstPointer => {
  // Creating a closure/fn-pointer or unsizing consumes
  // the input and stores it into the resulting rvalue.

src/librustc/middle/mem_categorization.rs

@@ -464,6 +464,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
  adjustment::Adjust::NeverToAny |
  adjustment::Adjust::ReifyFnPointer |
  adjustment::Adjust::UnsafeFnPointer |
+ adjustment::Adjust::ClosureFnPointer |
  adjustment::Adjust::MutToConstPointer |
  adjustment::Adjust::DerefRef {..} => {
  debug!("cat_expr({:?}): {:?}",

src/librustc/mir/mod.rs

@@ -1022,6 +1022,9 @@ pub enum CastKind {
  /// Convert unique, zero-sized type for a fn to fn()
  ReifyFnPointer,
 
+ /// Convert non capturing closure to fn()
+ ClosureFnPointer,
+
  /// Convert safe fn() to unsafe fn()
  UnsafeFnPointer,
 

src/librustc/ty/adjustment.rs

@@ -33,6 +33,9 @@ pub enum Adjust<'tcx> {
  /// Go from a safe fn pointer to an unsafe fn pointer.
  UnsafeFnPointer,
 
+ // Go from a non-capturing closure to an fn pointer.
+ ClosureFnPointer,
+
  /// Go from a mut raw pointer to a const raw pointer.
  MutToConstPointer,
 
@@ -120,6 +123,7 @@ impl<'tcx> Adjustment<'tcx> {
 
  Adjust::ReifyFnPointer |
  Adjust::UnsafeFnPointer |
+ Adjust::ClosureFnPointer |
  Adjust::MutToConstPointer |
  Adjust::DerefRef {..} => false,
  }

src/librustc_mir/build/expr/as_lvalue.rs

@@ -99,6 +99,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  ExprKind::Use { .. } |
  ExprKind::NeverToAny { .. } |
  ExprKind::ReifyFnPointer { .. } |
+ ExprKind::ClosureFnPointer { .. } |
  ExprKind::UnsafeFnPointer { .. } |
  ExprKind::Unsize { .. } |
  ExprKind::Repeat { .. } |

src/librustc_mir/build/expr/as_rvalue.rs

@@ -112,6 +112,10 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  let source = unpack!(block = this.as_operand(block, source));
  block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
  }
+ ExprKind::ClosureFnPointer { source } => {
+ let source = unpack!(block = this.as_operand(block, source));
+ block.and(Rvalue::Cast(CastKind::ClosureFnPointer, source, expr.ty))
+ }
  ExprKind::Unsize { source } => {
  let source = unpack!(block = this.as_operand(block, source));
  block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))

src/librustc_mir/build/expr/category.rs

@@ -70,6 +70,7 @@ impl Category {
  ExprKind::Cast { .. } |
  ExprKind::Use { .. } |
  ExprKind::ReifyFnPointer { .. } |
+ ExprKind::ClosureFnPointer { .. } |
  ExprKind::UnsafeFnPointer { .. } |
  ExprKind::Unsize { .. } |
  ExprKind::Repeat { .. } |

src/librustc_mir/build/expr/into.rs

@@ -244,6 +244,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  ExprKind::Cast { .. } |
  ExprKind::Use { .. } |
  ExprKind::ReifyFnPointer { .. } |
+ ExprKind::ClosureFnPointer { .. } |
  ExprKind::UnsafeFnPointer { .. } |
  ExprKind::Unsize { .. } |
  ExprKind::Repeat { .. } |

src/librustc_mir/hair/cx/expr.rs

@@ -60,6 +60,15 @@ impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
  kind: ExprKind::UnsafeFnPointer { source: expr.to_ref() },
  };
  }
+ Some((ty::adjustment::Adjust::ClosureFnPointer, adjusted_ty)) => {
+ expr = Expr {
+ temp_lifetime: temp_lifetime,
+ temp_lifetime_was_shrunk: was_shrunk,
+ ty: adjusted_ty,
+ span: self.span,
+ kind: ExprKind::ClosureFnPointer { source: expr.to_ref() },
+ };
+ }
  Some((ty::adjustment::Adjust::NeverToAny, adjusted_ty)) => {
  expr = Expr {
  temp_lifetime: temp_lifetime,

src/librustc_mir/hair/mod.rs

@@ -152,6 +152,9 @@ pub enum ExprKind<'tcx> {
  ReifyFnPointer {
  source: ExprRef<'tcx>,
  },
+ ClosureFnPointer {
+ source: ExprRef<'tcx>,
+ },
  UnsafeFnPointer {
  source: ExprRef<'tcx>,
  },

src/librustc_mir/transform/qualify_consts.rs

@@ -619,6 +619,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
  Rvalue::CheckedBinaryOp(..) |
  Rvalue::Cast(CastKind::ReifyFnPointer, ..) |
  Rvalue::Cast(CastKind::UnsafeFnPointer, ..) |
+ Rvalue::Cast(CastKind::ClosureFnPointer, ..) |
  Rvalue::Cast(CastKind::Unsize, ..) => {}
 
  Rvalue::Len(_) => {

src/librustc_passes/consts.rs

@@ -447,6 +447,7 @@ fn check_adjustments<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>, e: &hir::Exp
  Some(Adjust::NeverToAny) |
  Some(Adjust::ReifyFnPointer) |
  Some(Adjust::UnsafeFnPointer) |
+ Some(Adjust::ClosureFnPointer) |
  Some(Adjust::MutToConstPointer) => {}
 
  Some(Adjust::DerefRef { autoderefs, .. }) => {

src/librustc_trans/builder.rs

@@ -1188,7 +1188,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  }
 
  assert!(fn_ty.kind() == llvm::TypeKind::Function,
- "builder::{} not passed a function", typ);
+ "builder::{} not passed a function, but {:?}", typ, fn_ty);
 
  let param_tys = fn_ty.func_params();
 

src/librustc_trans/collector.rs

@@ -489,6 +489,20 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
  self.output);
  }
  }
+ mir::Rvalue::Cast(mir::CastKind::ClosureFnPointer, ref operand, _) => {
+ let source_ty = operand.ty(self.mir, self.scx.tcx());
+ match source_ty.sty {
+ ty::TyClosure(def_id, substs) => {
+ let closure_trans_item =
+ create_fn_trans_item(self.scx,
+ def_id,
+ substs.substs,
+ self.param_substs);
+ self.output.push(closure_trans_item);
+ }
+ _ => bug!(),
+ }
+ }
  mir::Rvalue::Box(..) => {
  let exchange_malloc_fn_def_id =
  self.scx

src/librustc_trans/mir/constant.rs

@@ -20,7 +20,7 @@ use rustc::mir;
 use rustc::mir::tcx::LvalueTy;
 use rustc::ty::{self, layout, Ty, TyCtxt, TypeFoldable};
 use rustc::ty::cast::{CastTy, IntTy};
-use rustc::ty::subst::Substs;
+use rustc::ty::subst::{Kind, Substs};
 use rustc_data_structures::indexed_vec::{Idx, IndexVec};
 use {abi, adt, base, Disr, machine};
 use callee::Callee;
@@ -578,6 +578,27 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
  }
  }
  }
+ mir::CastKind::ClosureFnPointer => {
+ match operand.ty.sty {
+ ty::TyClosure(def_id, substs) => {
+ // Get the def_id for FnOnce::call_once
+ let fn_once = tcx.lang_items.fn_once_trait().unwrap();
+ let call_once = tcx
+ .global_tcx().associated_items(fn_once)
+ .find(|it| it.kind == ty::AssociatedKind::Method)
+ .unwrap().def_id;
+ // Now create its substs [Closure, Tuple]
+ let input = tcx.closure_type(def_id, substs).sig.input(0);
+ let substs = tcx.mk_substs([operand.ty, input.skip_binder()]
+ .iter().cloned().map(Kind::from));
+ Callee::def(self.ccx, call_once, substs)
+ .reify(self.ccx)
+ }
+ _ => {
+ bug!("{} cannot be cast to a fn ptr", operand.ty)
+ }
+ }
+ }
  mir::CastKind::UnsafeFnPointer => {
  // this is a no-op at the LLVM level
  operand.llval

src/librustc_trans/mir/rvalue.rs

@@ -12,6 +12,7 @@ use llvm::{self, ValueRef};
 use rustc::ty::{self, Ty};
 use rustc::ty::cast::{CastTy, IntTy};
 use rustc::ty::layout::Layout;
+use rustc::ty::subst::Kind;
 use rustc::mir::tcx::LvalueTy;
 use rustc::mir;
 use middle::lang_items::ExchangeMallocFnLangItem;
@@ -190,6 +191,28 @@ impl<'a, 'tcx> MirContext<'a, 'tcx> {
  }
  }
  }
+ mir::CastKind::ClosureFnPointer => {
+ match operand.ty.sty {
+ ty::TyClosure(def_id, substs) => {
+ // Get the def_id for FnOnce::call_once
+ let fn_once = bcx.tcx().lang_items.fn_once_trait().unwrap();
+ let call_once = bcx.tcx()
+ .global_tcx().associated_items(fn_once)
+ .find(|it| it.kind == ty::AssociatedKind::Method)
+ .unwrap().def_id;
+ // Now create its substs [Closure, Tuple]
+ let input = bcx.tcx().closure_type(def_id, substs).sig.input(0);
+ let substs = bcx.tcx().mk_substs([operand.ty, input.skip_binder()]
+ .iter().cloned().map(Kind::from));
+ OperandValue::Immediate(
+ Callee::def(bcx.ccx, call_once, substs)
+ .reify(bcx.ccx))
+ }
+ _ => {
+ bug!("{} cannot be cast to a fn ptr", operand.ty)
+ }
+ }
+ }
  mir::CastKind::UnsafeFnPointer => {
  // this is a no-op at the LLVM level
  operand.val

src/librustc_typeck/check/coercion.rs

@@ -63,13 +63,17 @@
 use check::FnCtxt;
 
 use rustc::hir;
+use rustc::hir::def_id::DefId;
 use rustc::infer::{Coercion, InferOk, TypeTrace};
 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
-use rustc::ty::{self, LvaluePreference, TypeAndMut, Ty};
+use rustc::ty::{self, LvaluePreference, TypeAndMut,
+ Ty, ClosureSubsts};
 use rustc::ty::fold::TypeFoldable;
 use rustc::ty::error::TypeError;
 use rustc::ty::relate::RelateResult;
+use syntax::abi;
+use syntax::feature_gate;
 use util::common::indent;
 
 use std::cell::RefCell;
@@ -196,6 +200,11 @@ impl<'f, 'gcx, 'tcx> Coerce<'f, 'gcx, 'tcx> {
  // unsafe qualifier.
  self.coerce_from_fn_pointer(a, a_f, b)
  }
+ ty::TyClosure(def_id_a, substs_a) => {
+ // Non-capturing closures are coercible to
+ // function pointers
+ self.coerce_closure_to_fn(a, def_id_a, substs_a, b)
+ }
  _ => {
  // Otherwise, just use unification rules.
  self.unify_and_identity(a, b)
@@ -551,6 +560,60 @@ impl<'f, 'gcx, 'tcx> Coerce<'f, 'gcx, 'tcx> {
  }
  }
 
+ fn coerce_closure_to_fn(&self,
+ a: Ty<'tcx>,
+ def_id_a: DefId,
+ substs_a: ClosureSubsts<'tcx>,
+ b: Ty<'tcx>)
+ -> CoerceResult<'tcx> {
+ //! Attempts to coerce from the type of a non-capturing closure
+ //! into a function pointer.
+ //!
+
+ let b = self.shallow_resolve(b);
+
+ let node_id_a = self.tcx.hir.as_local_node_id(def_id_a).unwrap();
+ match b.sty {
+ ty::TyFnPtr(_) if self.tcx.with_freevars(node_id_a, |v| v.is_empty()) => {
+ if !self.tcx.sess.features.borrow().closure_to_fn_coercion {
+ feature_gate::emit_feature_err(&self.tcx.sess.parse_sess,
+ "closure_to_fn_coercion",
+ self.cause.span,
+ feature_gate::GateIssue::Language,
+ feature_gate::CLOSURE_TO_FN_COERCION);
+ return self.unify_and_identity(a, b);
+ }
+ // We coerce the closure, which has fn type
+ // `extern "rust-call" fn((arg0,arg1,...)) -> _`
+ // to
+ // `fn(arg0,arg1,...) -> _`
+ let sig = self.closure_type(def_id_a, substs_a).sig;
+ let converted_sig = sig.map_bound(|s| {
+ let params_iter = match s.inputs()[0].sty {
+ ty::TyTuple(params, _) => {
+ params.into_iter().cloned()
+ }
+ _ => bug!(),
+ };
+ self.tcx.mk_fn_sig(params_iter,
+ s.output(),
+ s.variadic)
+ });
+ let fn_ty = self.tcx.mk_bare_fn(ty::BareFnTy {
+ unsafety: hir::Unsafety::Normal,
+ abi: abi::Abi::Rust,
+ sig: converted_sig,
+ });
+ let pointer_ty = self.tcx.mk_fn_ptr(&fn_ty);
+ debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})",
+ a, b, pointer_ty);
+ self.unify_and_identity(pointer_ty, b)
+ .map(|(ty, _)| (ty, Adjust::ClosureFnPointer))
+ }
+ _ => self.unify_and_identity(a, b),
+ }
+ }
+
  fn coerce_unsafe_ptr(&self,
  a: Ty<'tcx>,
  b: Ty<'tcx>,

src/librustc_typeck/check/writeback.rs

@@ -412,6 +412,10 @@ impl<'cx, 'gcx, 'tcx> WritebackCx<'cx, 'gcx, 'tcx> {
  adjustment::Adjust::MutToConstPointer
  }
 
+ adjustment::Adjust::ClosureFnPointer => {
+ adjustment::Adjust::ClosureFnPointer
+ }
+
  adjustment::Adjust::UnsafeFnPointer => {
  adjustment::Adjust::UnsafeFnPointer
  }

src/libsyntax/feature_gate.rs

@@ -326,6 +326,10 @@ declare_features! (
  // `extern "msp430-interrupt" fn()`
  (active, abi_msp430_interrupt, "1.16.0", Some(38487)),
 
+ // Used to identify crates that contain sanitizer runtimes
+ // rustc internal
+ (active, closure_to_fn_coercion, "1.17.0", Some(39817)),
+
  // Used to identify crates that contain sanitizer runtimes
  // rustc internal
  (active, sanitizer_runtime, "1.17.0", None),
@@ -982,6 +986,9 @@ pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
 pub const EXPLAIN_PLACEMENT_IN: &'static str =
  "placement-in expression syntax is experimental and subject to change.";
 
+pub const CLOSURE_TO_FN_COERCION: &'static str =
+ "non-capturing closure to fn coercion is experimental";
+
 struct PostExpansionVisitor<'a> {
  context: &'a Context<'a>,
 }

src/test/compile-fail/closure-no-fn.rs

@@ -0,0 +1,24 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Ensure that capturing closures are never coerced to fns
+// Especially interesting as non-capturing closures can be.
+
+fn main() {
+ let mut a = 0u8;
+ let foo: fn(u8) -> u8 = |v: u8| { a += v; a };
+ //~^ ERROR mismatched types
+ let b = 0u8;
+ let bar: fn() -> u8 = || { b };
+ //~^ ERROR mismatched types
+ let baz: fn() -> u8 = || { b } as fn() -> u8;
+ //~^ ERROR mismatched types
+ //~^^ ERROR non-scalar cast
+}