Rollup merge of rust-lang#56845 - GuillaumeGomez:const-docs, r=oli-obk

Don't render const keyword on stable

Fixes rust-lang#55246.

Continuation of rust-lang#55327.

r? @oli-obk

Author: pietroalbini

src/librustdoc/clean/inline.rs

@@ -207,7 +207,7 @@ pub fn build_external_trait(cx: &DocContext, did: DefId) -> clean::Trait {
 fn build_external_function(cx: &DocContext, did: DefId) -> clean::Function {
     let sig = cx.tcx.fn_sig(did);
 
-    let constness = if cx.tcx.is_const_fn(did) {
+    let constness = if cx.tcx.is_min_const_fn(did) {
         hir::Constness::Const
     } else {
         hir::Constness::NotConst

src/librustdoc/clean/mod.rs

@@ -1674,18 +1674,24 @@ impl Clean<Item> for doctree::Function {
             (self.generics.clean(cx), (&self.decl, self.body).clean(cx))
         });
 
+        let did = cx.tcx.hir().local_def_id(self.id);
+        let constness = if cx.tcx.is_min_const_fn(did) {
+            hir::Constness::Const
+        } else {
+            hir::Constness::NotConst
+        };
         Item {
             name: Some(self.name.clean(cx)),
             attrs: self.attrs.clean(cx),
             source: self.whence.clean(cx),
             visibility: self.vis.clean(cx),
             stability: self.stab.clean(cx),
             deprecation: self.depr.clean(cx),
-            def_id: cx.tcx.hir().local_def_id(self.id),
+            def_id: did,
             inner: FunctionItem(Function {
                 decl,
                 generics,
-                header: self.header,
+                header: hir::FnHeader { constness, ..self.header },
             }),
         }
     }
@@ -2009,7 +2015,7 @@ impl<'tcx> Clean<Item> for ty::AssociatedItem {
                     ty::TraitContainer(_) => self.defaultness.has_value()
                 };
                 if provided {
-                    let constness = if cx.tcx.is_const_fn(self.def_id) {
+                    let constness = if cx.tcx.is_min_const_fn(self.def_id) {
                         hir::Constness::Const
                     } else {
                         hir::Constness::NotConst

src/test/rustdoc/const-display.rs

@@ -0,0 +1,43 @@
+// Copyright 2018 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_name = "foo"]
+
+#![unstable(feature = "humans",
+            reason = "who ever let humans program computers, we're apparently really bad at it",
+            issue = "0")]
+
+#![feature(rustc_const_unstable, const_fn, foo, foo2)]
+#![feature(min_const_unsafe_fn)]
+#![feature(staged_api)]
+
+// @has 'foo/fn.foo.html' '//pre' 'pub unsafe fn foo() -> u32'
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_const_unstable(feature="foo")]
+pub const unsafe fn foo() -> u32 { 42 }
+
+// @has 'foo/fn.foo2.html' '//pre' 'pub fn foo2() -> u32'
+#[unstable(feature = "humans", issue="0")]
+pub const fn foo2() -> u32 { 42 }
+
+// @has 'foo/fn.bar2.html' '//pre' 'pub const fn bar2() -> u32'
+#[stable(feature = "rust1", since = "1.0.0")]
+pub const fn bar2() -> u32 { 42 }
+
+// @has 'foo/fn.foo2_gated.html' '//pre' 'pub unsafe fn foo2_gated() -> u32'
+#[unstable(feature = "foo2", issue="0")]
+pub const unsafe fn foo2_gated() -> u32 { 42 }
+
+// @has 'foo/fn.bar2_gated.html' '//pre' 'pub const unsafe fn bar2_gated() -> u32'
+#[stable(feature = "rust1", since = "1.0.0")]
+pub const unsafe fn bar2_gated() -> u32 { 42 }
+
+// @has 'foo/fn.bar_not_gated.html' '//pre' 'pub unsafe fn bar_not_gated() -> u32'
+pub const unsafe fn bar_not_gated() -> u32 { 42 }