Rollup merge of rust-lang#48014 - Manishearth:stealing-chickens-on-the-internet, r=nikomatsakis

Implement RFC 2052 (Epochs)

This adds -Zepochs and uses it for tyvar_behind_raw_pointer (rust-lang#46906)

When we move this to --epoch=XXX, we'll need to gate the 2018 epoch on nightly, but not the 2015 one. I can make these changes here itself though it's kinda pointless given that the entire flag is nightly-only.

r? @nikomatsakis @aturon

cc rust-lang#44581 (epoch tracking)
cc rust-lang#46906 (tyvar_behind_raw_pointer)

Author: Manishearth

src/librustc/lib.rs

@@ -58,6 +58,7 @@
 #![feature(macro_vis_matcher)]
 #![feature(match_default_bindings)]
 #![feature(never_type)]
+#![feature(non_exhaustive)]
 #![feature(nonzero)]
 #![feature(quote)]
 #![feature(refcell_replace_swap)]

src/librustc/session/config.rs

@@ -112,6 +112,31 @@ pub enum OutputType {
     DepInfo,
 }
 
+/// The epoch of the compiler (RFC 2052)
+#[derive(Clone, Copy, Hash, PartialOrd, Ord, Eq, PartialEq)]
+#[non_exhaustive]
+pub enum Epoch {
+    // epochs must be kept in order, newest to oldest
+
+    /// The 2015 epoch
+    Epoch2015,
+    /// The 2018 epoch
+    Epoch2018,
+
+    // when adding new epochs, be sure to update:
+    //
+    // - the list in the `parse_epoch` static
+    // - the match in the `parse_epoch` function
+    // - add a `rust_####()` function to the session
+    // - update the enum in Cargo's sources as well
+    //
+    // When -Zepoch becomes --epoch, there will
+    // also be a check for the epoch being nightly-only
+    // somewhere. That will need to be updated
+    // whenever we're stabilizing/introducing a new epoch
+    // as well as changing the default Cargo template.
+}
+
 impl_stable_hash_for!(enum self::OutputType {
     Bitcode,
     Assembly,
@@ -783,11 +808,13 @@ macro_rules! options {
             Some("`string` or `string=string`");
         pub const parse_lto: Option<&'static str> =
             Some("one of `thin`, `fat`, or omitted");
+        pub const parse_epoch: Option<&'static str> =
+            Some("one of: `2015`, `2018`");
     }
 
     #[allow(dead_code)]
     mod $mod_set {
-        use super::{$struct_name, Passes, SomePasses, AllPasses, Sanitizer, Lto};
+        use super::{$struct_name, Passes, SomePasses, AllPasses, Sanitizer, Lto, Epoch};
         use rustc_back::{LinkerFlavor, PanicStrategy, RelroLevel};
         use std::path::PathBuf;
 
@@ -991,6 +1018,15 @@ macro_rules! options {
             };
             true
         }
+
+        fn parse_epoch(slot: &mut Epoch, v: Option<&str>) -> bool {
+            match v {
+                Some("2015") => *slot = Epoch::Epoch2015,
+                Some("2018") => *slot = Epoch::Epoch2018,
+                _ => return false,
+            }
+            true
+        }
     }
 ) }
 
@@ -1278,6 +1314,10 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         `everybody_loops` (all function bodies replaced with `loop {}`),
         `hir` (the HIR), `hir,identified`, or
         `hir,typed` (HIR with types for each node)."),
+    epoch: Epoch = (Epoch::Epoch2015, parse_epoch, [TRACKED],
+        "The epoch to build Rust with. Newer epochs may include features
+         that require breaking changes. The default epoch is 2015 (the first
+         epoch). Crates compiled with different epochs can be linked together."),
 }
 
 pub fn default_lib_output() -> CrateType {
@@ -2069,7 +2109,7 @@ mod dep_tracking {
     use std::path::PathBuf;
     use std::collections::hash_map::DefaultHasher;
     use super::{Passes, CrateType, OptLevel, DebugInfoLevel, Lto,
-                OutputTypes, Externs, ErrorOutputType, Sanitizer};
+                OutputTypes, Externs, ErrorOutputType, Sanitizer, Epoch};
     use syntax::feature_gate::UnstableFeatures;
     use rustc_back::{PanicStrategy, RelroLevel};
 
@@ -2131,6 +2171,7 @@ mod dep_tracking {
     impl_dep_tracking_hash_via_hash!(cstore::NativeLibraryKind);
     impl_dep_tracking_hash_via_hash!(Sanitizer);
     impl_dep_tracking_hash_via_hash!(Option<Sanitizer>);
+    impl_dep_tracking_hash_via_hash!(Epoch);
 
     impl_dep_tracking_hash_for_sortable_vec_of!(String);
     impl_dep_tracking_hash_for_sortable_vec_of!(PathBuf);

src/librustc/session/mod.rs

@@ -19,7 +19,7 @@ use lint;
 use middle::allocator::AllocatorKind;
 use middle::dependency_format;
 use session::search_paths::PathKind;
-use session::config::{BorrowckMode, DebugInfoLevel, OutputType};
+use session::config::{BorrowckMode, DebugInfoLevel, OutputType, Epoch};
 use ty::tls;
 use util::nodemap::{FxHashMap, FxHashSet};
 use util::common::{duration_to_secs_str, ErrorReported};
@@ -864,6 +864,11 @@ impl Session {
     pub fn teach(&self, code: &DiagnosticId) -> bool {
         self.opts.debugging_opts.teach && !self.parse_sess.span_diagnostic.code_emitted(code)
     }
+
+    /// Are we allowed to use features from the Rust 2018 epoch?
+    pub fn rust_2018(&self) -> bool {
+        self.opts.debugging_opts.epoch >= Epoch::Epoch2018
+    }
 }
 
 pub fn build_session(sopts: config::Options,

src/librustc_typeck/check/method/probe.rs

@@ -326,13 +326,19 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     if reached_raw_pointer
                     && !self.tcx.sess.features.borrow().arbitrary_self_types {
                         // this case used to be allowed by the compiler,
-                        // so we do a future-compat lint here
+                        // so we do a future-compat lint here for the 2015 epoch
                         // (see https://github.com/rust-lang/rust/issues/46906)
-                        self.tcx.lint_node(
-                            lint::builtin::TYVAR_BEHIND_RAW_POINTER,
-                            scope_expr_id,
-                            span,
-                            &format!("the type of this value must be known in this context"));
+                        if self.tcx.sess.rust_2018() {
+                          span_err!(self.tcx.sess, span, E0908,
+                                    "the type of this value must be known \
+                                     to call a method on a raw pointer on it");
+                        } else {
+                            self.tcx.lint_node(
+                                lint::builtin::TYVAR_BEHIND_RAW_POINTER,
+                                scope_expr_id,
+                                span,
+                                &format!("the type of this value must be known in this context"));
+                        }
                     } else {
                         let t = self.structurally_resolved_type(span, final_ty);
                         assert_eq!(t, self.tcx.types.err);

src/librustc_typeck/diagnostics.rs

@@ -4698,6 +4698,55 @@ element type `T`. Also note that the error is conservatively reported even when
 the alignment of the zero-sized type is less than or equal to the data field's
 alignment.
 "##,
+
+
+E0908: r##"
+A method was called on a raw pointer whose inner type wasn't completely known.
+
+For example, you may have done something like:
+
+```compile_fail
+# #![deny(warnings)]
+let foo = &1;
+let bar = foo as *const _;
+if bar.is_null() {
+    // ...
+}
+```
+
+Here, the type of `bar` isn't known; it could be a pointer to anything. Instead,
+specify a type for the pointer (preferably something that makes sense for the
+thing you're pointing to):
+
+```
+let foo = &1;
+let bar = foo as *const i32;
+if bar.is_null() {
+    // ...
+}
+```
+
+Even though `is_null()` exists as a method on any raw pointer, Rust shows this
+error because  Rust allows for `self` to have arbitrary types (behind the
+arbitrary_self_types feature flag).
+
+This means that someone can specify such a function:
+
+```ignore (cannot-doctest-feature-doesnt-exist-yet)
+impl Foo {
+    fn is_null(self: *const Self) -> bool {
+        // do something else
+    }
+}
+```
+
+and now when you call `.is_null()` on a raw pointer to `Foo`, there's ambiguity.
+
+Given that we don't know what type the pointer is, and there's potential
+ambiguity for some types, we disallow calling methods on raw pointers when
+the type is unknown.
+"##,
+
 }
 
 register_diagnostics! {

src/test/compile-fail/epoch-raw-pointer-method-2015.rs

@@ -0,0 +1,23 @@
+// 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.
+
+// ignore-tidy-linelength
+// compile-flags: -Zepoch=2015 -Zunstable-options
+
+// tests that epochs work with the tyvar warning-turned-error
+
+#[deny(warnings)]
+fn main() {
+    let x = 0;
+    let y = &x as *const _;
+    let _ = y.is_null();
+    //~^ error: the type of this value must be known in this context [tyvar_behind_raw_pointer]
+    //~^^ warning: this was previously accepted
+}

src/test/compile-fail/epoch-raw-pointer-method-2018.rs

@@ -0,0 +1,22 @@
+// 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.
+
+// ignore-tidy-linelength
+// compile-flags: -Zepoch=2018 -Zunstable-options
+
+// tests that epochs work with the tyvar warning-turned-error
+
+#[deny(warnings)]
+fn main() {
+    let x = 0;
+    let y = &x as *const _;
+    let _ = y.is_null();
+    //~^ error: the type of this value must be known to call a method on a raw pointer on it [E0908]
+}