Auto merge of #25880 - nikomatsakis:const-fn-feature-gate-calls, r=alexcrichton

The previous feature gate assumed we would not define any (stable) const fns. But then @eddyb went and cleaned up the code. So this now extends the feature-gate to prohibit calls; but calls inside of macros are considered ok.

r? @alexcrichton

src/libcollectionstest/lib.rs

@@ -14,6 +14,7 @@
 #![feature(collections)]
 #![feature(collections_drain)]
 #![feature(core)]
+#![feature(const_fn)]
 #![feature(hash)]
 #![feature(rand)]
 #![feature(rustc_private)]

src/libcoretest/lib.rs

@@ -14,6 +14,7 @@
 #![feature(box_syntax)]
 #![feature(unboxed_closures)]
 #![feature(core)]
+#![feature(const_fn)]
 #![feature(test)]
 #![feature(rand)]
 #![feature(unicode)]

src/liblog/lib.rs

@@ -173,6 +173,7 @@
 #![feature(staged_api)]
 #![feature(box_syntax)]
 #![feature(core)]
+#![feature(const_fn)]
 #![feature(std_misc)]
 
 use std::boxed;

src/librustc/lib.rs

@@ -29,6 +29,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(collections)]
+#![feature(const_fn)]
 #![feature(core)]
 #![feature(duration)]
 #![feature(duration_span)]

src/librustc/middle/check_const.rs

@@ -199,8 +199,32 @@ impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
     }
 
     /// Returns true if the call is to a const fn or method.
-    fn handle_const_fn_call(&mut self, def_id: ast::DefId, ret_ty: Ty<'tcx>) -> bool {
+    fn handle_const_fn_call(&mut self,
+                            expr: &ast::Expr,
+                            def_id: ast::DefId,
+                            ret_ty: Ty<'tcx>)
+                            -> bool {
         if let Some(fn_like) = const_eval::lookup_const_fn_by_id(self.tcx, def_id) {
+            if
+                // we are in a static/const initializer
+                self.mode != Mode::Var &&
+
+                // feature-gate is not enabled
+                !self.tcx.sess.features.borrow().const_fn &&
+
+                // this doesn't come from a macro that has #[allow_internal_unstable]
+                !self.tcx.sess.codemap().span_allows_unstable(expr.span)
+            {
+                self.tcx.sess.span_err(
+                    expr.span,
+                    &format!("const fns are an unstable feature"));
+                fileline_help!(
+                    self.tcx.sess,
+                    expr.span,
+                    "in Nightly builds, add `#![feature(const_fn)]` to the crate \
+                     attributes to enable");
+            }
+
             let qualif = self.fn_like(fn_like.kind(),
                                       fn_like.decl(),
                                       fn_like.body(),
@@ -657,7 +681,7 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
                 }
                 Some(def::DefMethod(did, def::FromImpl(_))) |
                 Some(def::DefFn(did, _)) => {
-                    v.handle_const_fn_call(did, node_ty)
+                    v.handle_const_fn_call(e, did, node_ty)
                 }
                 _ => false
             };
@@ -677,7 +701,7 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
                 _ => None
             };
             let is_const = match method_did {
-                Some(did) => v.handle_const_fn_call(did, node_ty),
+                Some(did) => v.handle_const_fn_call(e, did, node_ty),
                 None => false
             };
             if !is_const {

src/librustc_trans/lib.rs

@@ -30,6 +30,7 @@
 #![feature(box_syntax)]
 #![feature(collections)]
 #![feature(core)]
+#![feature(const_fn)]
 #![feature(libc)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]

src/libsyntax/feature_gate.rs

@@ -332,7 +332,8 @@ pub struct Features {
     /// spans of #![feature] attrs for stable language features. for error reporting
     pub declared_stable_lang_features: Vec<Span>,
     /// #![feature] attrs for non-language (library) features
-    pub declared_lib_features: Vec<(InternedString, Span)>
+    pub declared_lib_features: Vec<(InternedString, Span)>,
+    pub const_fn: bool,
 }
 
 impl Features {
@@ -352,7 +353,8 @@ impl Features {
             unmarked_api: false,
             negate_unsigned: false,
             declared_stable_lang_features: Vec::new(),
-            declared_lib_features: Vec::new()
+            declared_lib_features: Vec::new(),
+            const_fn: false,
         }
     }
 }
@@ -802,7 +804,8 @@ fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler,
         unmarked_api: cx.has_feature("unmarked_api"),
         negate_unsigned: cx.has_feature("negate_unsigned"),
         declared_stable_lang_features: accepted_features,
-        declared_lib_features: unknown_features
+        declared_lib_features: unknown_features,
+        const_fn: cx.has_feature("const_fn"),
     }
 }
 

src/test/auxiliary/const_fn_lib.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+// Crate that exports a const fn. Used for testing cross-crate.
+
+#![crate_type="rlib"]
+#![feature(const_fn)]
+
+pub const fn foo() -> usize { 22 } //~ ERROR const fn is unstable

src/test/auxiliary/issue-17718.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(const_fn)]
+
 use std::sync::atomic;
 
 pub const C1: usize = 1;

src/test/compile-fail/const-fn-stability-calls-2.rs

@@ -0,0 +1,21 @@
+// Copyright 2015 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.
+
+// Test use of const fn from another crate without a feature gate.
+
+// aux-build:const_fn_lib.rs
+
+extern crate const_fn_lib;
+
+use const_fn_lib::foo;
+
+fn main() {
+    let x: [usize; foo()] = []; //~ ERROR unsupported constant expr
+}

src/test/compile-fail/const-fn-stability-calls-3.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 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.
+
+// Test use of const fn from another crate without a feature gate.
+
+#![feature(rustc_attrs)]
+#![allow(unused_variables)]
+
+// aux-build:const_fn_lib.rs
+
+extern crate const_fn_lib;
+
+use const_fn_lib::foo;
+
+#[rustc_error]
+fn main() { //~ ERROR compilation successful
+    let x = foo(); // use outside a constant is ok
+}

src/test/compile-fail/const-fn-stability-calls.rs

@@ -0,0 +1,34 @@
+// Copyright 2015 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.
+
+// Test use of const fn from another crate without a feature gate.
+
+// aux-build:const_fn_lib.rs
+
+extern crate const_fn_lib;
+
+use const_fn_lib::foo;
+
+static FOO: usize = foo(); //~ ERROR const fns are an unstable feature
+const BAR: usize = foo(); //~ ERROR const fns are an unstable feature
+
+macro_rules! constant {
+    ($n:ident: $t:ty = $v:expr) => {
+        const $n: $t = $v;
+    }
+}
+
+constant! {
+    BAZ: usize = foo() //~ ERROR const fns are an unstable feature
+}
+
+fn main() {
+//    let x: [usize; foo()] = [];
+}

src/test/compile-fail/const-fn-stability.rs

@@ -25,4 +25,19 @@ impl Foo for u32 {
     const fn foo() -> u32 { 0 } //~ ERROR const fn is unstable
 }
 
-fn main() { }
+static FOO: usize = foo();
+const BAR: usize = foo();
+
+macro_rules! constant {
+    ($n:ident: $t:ty = $v:expr) => {
+        const $n: $t = $v;
+    }
+}
+
+constant! {
+    BAZ: usize = foo()
+}
+
+fn main() {
+    let x: [usize; foo()] = [];
+}

src/test/compile-fail/dropck_arr_cycle_checked.rs

@@ -13,6 +13,8 @@
 //
 // (Compare against compile-fail/dropck_vec_cycle_checked.rs)
 
+#![feature(const_fn)]
+
 use std::cell::Cell;
 use id::Id;
 

src/test/compile-fail/dropck_tarena_cycle_checked.rs

@@ -17,6 +17,7 @@
 //  for the error message we see here.)
 
 #![allow(unstable)]
+#![feature(const_fn)]
 
 extern crate arena;
 

src/test/compile-fail/dropck_trait_cycle_checked.rs

@@ -13,6 +13,8 @@
 //
 // (Compare against compile-fail/dropck_vec_cycle_checked.rs)
 
+#![feature(const_fn)]
+
 use std::cell::Cell;
 use id::Id;
 

src/test/compile-fail/dropck_vec_cycle_checked.rs

@@ -12,6 +12,8 @@
 //
 // (Compare against compile-fail/dropck_arr_cycle_checked.rs)
 
+#![feature(const_fn)]
+
 use std::cell::Cell;
 use id::Id;
 

src/test/compile-fail/functional-struct-update-respects-privacy.rs

@@ -10,6 +10,8 @@
 
 // RFC 736 (and Issue 21407): functional struct update should respect privacy.
 
+#![feature(const_fn)]
+
 // The `foo` module attempts to maintains an invariant that each `S`
 // has a unique `u64` id.
 use self::foo::S;

src/test/compile-fail/issue-17718-const-borrow.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(const_fn)]
+
 use std::cell::UnsafeCell;
 
 const A: UnsafeCell<usize> = UnsafeCell::new(1);

src/test/compile-fail/issue-7364.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![feature(box_syntax)]
+#![feature(const_fn)]
 
 use std::cell::RefCell;
 

src/test/compile-fail/vec-must-not-hide-type-from-dropck.rs

@@ -23,6 +23,8 @@
 // conditions above to be satisfied, meaning that if the dropck is
 // sound, it should reject this code.
 
+#![feature(const_fn)]
+
 use std::cell::Cell;
 use id::Id;
 

src/test/debuginfo/constant-debug-locs.rs

@@ -15,6 +15,7 @@
 #![allow(dead_code, unused_variables)]
 #![omit_gdb_pretty_printer_section]
 #![feature(std_misc, core)]
+#![feature(const_fn)]
 
 // This test makes sure that the compiler doesn't crash when trying to assign
 // debug locations to const-expressions.

src/test/run-pass-valgrind/cast-enum-with-dtor.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 #![allow(dead_code)]
+#![feature(const_fn)]
 
 // check dtor calling order when casting enums.
 

src/test/run-pass/associated-types-project-from-type-param-via-bound-in-where-clause.rs

@@ -12,6 +12,8 @@
 // `Item` originates in a where-clause, not the declaration of
 // `T`. Issue #20300.
 
+#![feature(const_fn)]
+
 use std::marker::{PhantomData};
 use std::sync::atomic::{AtomicUsize};
 use std::sync::atomic::Ordering::SeqCst;

src/test/run-pass/box-of-array-of-drop-1.rs

@@ -11,6 +11,8 @@
 // Test that we cleanup a fixed size Box<[D; k]> properly when D has a
 // destructor.
 
+#![feature(const_fn)]
+
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};
 

src/test/run-pass/box-of-array-of-drop-2.rs

@@ -11,6 +11,8 @@
 // Test that we cleanup dynamic sized Box<[D]> properly when D has a
 // destructor.
 
+#![feature(const_fn)]
+
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};
 

src/test/run-pass/const-fn-cross-crate.rs

@@ -0,0 +1,25 @@
+// Copyright 2015 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.
+
+// aux-build:const_fn_lib.rs
+
+// A very basic test of const fn functionality.
+
+#![feature(const_fn)]
+
+extern crate const_fn_lib;
+
+use const_fn_lib::foo;
+
+const FOO: usize = foo();
+
+fn main() {
+    assert_eq!(FOO, 22);
+}

src/test/run-pass/const-fn-method.rs

@@ -0,0 +1,25 @@
+// Copyright 2012 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.
+
+#![feature(const_fn)]
+
+struct Foo { value: u32 }
+
+impl Foo {
+    const fn new() -> Foo {
+        Foo { value: 22 }
+    }
+}
+
+const FOO: Foo = Foo::new();
+
+pub fn main() {
+    assert_eq!(FOO.value, 22);
+}

src/test/run-pass/issue-17718-static-unsafe-interior.rs

@@ -11,6 +11,8 @@
 // pretty-expanded FIXME #23616
 
 #![feature(core)]
+#![feature(const_fn)]
+
 
 use std::marker;
 use std::cell::UnsafeCell;

src/test/run-pass/issue-17718.rs

@@ -12,6 +12,7 @@
 
 
 #![feature(core)]
+#![feature(const_fn)]
 
 extern crate issue_17718 as other;
 

src/test/run-pass/issue-21486.rs

@@ -12,6 +12,7 @@
 // created via FRU and control-flow breaks in the middle of
 // construction.
 
+#![feature(const_fn)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/nested-vec-3.rs

@@ -12,6 +12,7 @@
 // the contents implement Drop and we hit a panic in the middle of
 // construction.
 
+#![feature(const_fn)]
 
 use std::thread;
 use std::sync::atomic::{AtomicUsize, Ordering};

src/test/run-pass/struct-order-of-eval-3.rs

@@ -11,6 +11,7 @@
 // Checks that functional-record-update order-of-eval is as expected
 // even when no Drop-implementations are involved.
 
+#![feature(const_fn)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/struct-order-of-eval-4.rs

@@ -11,6 +11,7 @@
 // Checks that struct-literal expression order-of-eval is as expected
 // even when no Drop-implementations are involved.
 
+#![feature(const_fn)]
 
 use std::sync::atomic::{Ordering, AtomicUsize};
 

src/test/run-pass/vector-sort-panic-safe.rs

@@ -10,6 +10,7 @@
 
 
 #![feature(rand, core)]
+#![feature(const_fn)]
 
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::__rand::{thread_rng, Rng};