Rollup merge of #49179 - varkor:future-deprecation, r=QuietMisdreavus,GuillaumeGomez

Handle future deprecation annotations

This adds special handling to the `since` parameter of the `deprecated` attribute: in particular, if the `since` version exceeds the version of the compiler, the deprecation notice will not be printed; but a note is added to the documentation stating that the item will be deprecated in a later version.

(I've used `since` for this, rather than adding a new attribute, because it's more seamless and, I feel, intuitive. Plus it involves less code churn.)

![image](https://user-images.githubusercontent.com/3943692/37611317-ef5cdf16-2b99-11e8-8251-e35e8f7b0137.png)
![image](https://user-images.githubusercontent.com/3943692/37611323-f748c2d0-2b99-11e8-966b-11408c73d416.png)

This is a prerequisite for doing things renaming methods in the standard library (e.g. #30459). Resolves #30785.

src/librustc/middle/stability.rs

@@ -470,6 +470,30 @@ pub fn check_unstable_api_usage<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
     tcx.hir.krate().visit_all_item_likes(&mut checker.as_deep_visitor());
 }
 
+/// Check whether an item marked with `deprecated(since="X")` is currently
+/// deprecated (i.e. whether X is not greater than the current rustc version).
+pub fn deprecation_in_effect(since: &str) -> bool {
+    fn parse_version(ver: &str) -> Vec<u32> {
+        // We ignore non-integer components of the version (e.g. "nightly").
+        ver.split(|c| c == '.' || c == '-').flat_map(|s| s.parse()).collect()
+    }
+
+    if let Some(rustc) = option_env!("CFG_RELEASE") {
+        let since: Vec<u32> = parse_version(since);
+        let rustc: Vec<u32> = parse_version(rustc);
+        // We simply treat invalid `since` attributes as relating to a previous
+        // Rust version, thus always displaying the warning.
+        if since.len() != 3 {
+            return true;
+        }
+        since <= rustc
+    } else {
+        // By default, a deprecation warning applies to
+        // the current version of the compiler.
+        true
+    }
+}
+
 struct Checker<'a, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 }
@@ -559,9 +583,19 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         // Deprecated attributes apply in-crate and cross-crate.
         if let Some(id) = id {
             if let Some(depr_entry) = self.lookup_deprecation_entry(def_id) {
+                // If the deprecation is scheduled for a future Rust
+                // version, then we should display no warning message.
+                let deprecated_in_future_version = if let Some(sym) = depr_entry.attr.since {
+                    let since = sym.as_str();
+                    !deprecation_in_effect(&since)
+                } else {
+                    false
+                };
+
                 let parent_def_id = self.hir.local_def_id(self.hir.get_parent(id));
-                let skip = self.lookup_deprecation_entry(parent_def_id)
-                    .map_or(false, |parent_depr| parent_depr.same_origin(&depr_entry));
+                let skip = deprecated_in_future_version ||
+                           self.lookup_deprecation_entry(parent_def_id)
+                               .map_or(false, |parent_depr| parent_depr.same_origin(&depr_entry));
                 if !skip {
                     lint_deprecated(def_id, id, depr_entry.attr.note);
                 }

src/librustdoc/html/render.rs

@@ -2113,9 +2113,15 @@ fn short_stability(item: &clean::Item, cx: &Context, show_reason: bool) -> Vec<S
             } else {
                 String::new()
             };
-            let text = format!("Deprecated{}{}",
-                               since,
-                               MarkdownHtml(&deprecated_reason));
+            let text = if stability::deprecation_in_effect(&stab.deprecated_since) {
+                format!("Deprecated{}{}",
+                        since,
+                        MarkdownHtml(&deprecated_reason))
+            } else {
+                format!("Deprecating in {}{}",
+                        Escape(&stab.deprecated_since),
+                        MarkdownHtml(&deprecated_reason))
+            };
             stability.push(format!("<div class='stab deprecated'>{}</div>", text))
         };
 
@@ -2165,7 +2171,15 @@ fn short_stability(item: &clean::Item, cx: &Context, show_reason: bool) -> Vec<S
             String::new()
         };
 
-        let text = format!("Deprecated{}{}", since, MarkdownHtml(&note));
+        let text = if stability::deprecation_in_effect(&depr.since) {
+            format!("Deprecated{}{}",
+                    since,
+                    MarkdownHtml(&note))
+        } else {
+            format!("Deprecating in {}{}",
+                    Escape(&depr.since),
+                    MarkdownHtml(&note))
+        };
         stability.push(format!("<div class='stab deprecated'>{}</div>", text))
     }
 

src/test/compile-fail/deprecation-lint.rs

@@ -180,6 +180,11 @@ mod this_crate {
     #[deprecated(since = "1.0.0", note = "text")]
     pub fn deprecated_text() {}
 
+    #[deprecated(since = "99.99.99", note = "text")]
+    pub fn deprecated_future() {}
+    #[deprecated(since = "99.99.99", note = "text")]
+    pub fn deprecated_future_text() {}
+
     pub struct MethodTester;
 
     impl MethodTester {
@@ -266,6 +271,9 @@ mod this_crate {
         <Foo>::trait_deprecated_text(&foo); //~ ERROR use of deprecated item 'this_crate::Trait::trait_deprecated_text': text
         <Foo as Trait>::trait_deprecated_text(&foo); //~ ERROR use of deprecated item 'this_crate::Trait::trait_deprecated_text': text
 
+        deprecated_future(); // Fine; no error.
+        deprecated_future_text(); // Fine; no error.
+
         let _ = DeprecatedStruct {
             //~^ ERROR use of deprecated item 'this_crate::DeprecatedStruct': text
             i: 0 //~ ERROR use of deprecated item 'this_crate::DeprecatedStruct::i': text

src/test/rustdoc/deprecated-future.rs

@@ -0,0 +1,16 @@
+// 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.
+
+#![feature(deprecated)]
+
+// @has deprecated_future/struct.S.html '//*[@class="stab deprecated"]' \
+//      'Deprecating in 99.99.99: effectively never'
+#[deprecated(since = "99.99.99", note = "effectively never")]
+pub struct S;