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

Author: bors

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
+}