Auto merge of #44167 - cengizIO:master, r=nikomatsakis

Improve SubSupConflict with a named and an anonymous lifetime parameter #42701

Hello!

This fixes #42701.

## UPDATE 01
Tests are producing different results between different env builds.
This inconsistency might take a long time to investigate and fix. So, be patient

## UPDATE 02
Changed an `FxHashMap` with a `BTreeMap`. Inconsistency seems to be resolved for now.

Author: bors

src/librustc/infer/error_reporting/different_lifetimes.rs

@@ -60,6 +60,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn try_report_anon_anon_conflict(&self, error: &RegionResolutionError<'tcx>) -> bool {
         let (span, sub, sup) = match *error {
             ConcreteFailure(ref origin, sub, sup) => (origin.span(), sub, sup),
+            SubSupConflict(_, ref origin, sub, _, sup) => (origin.span(), sub, sup),
             _ => return false, // inapplicable
         };
 

src/librustc/infer/error_reporting/named_anon_conflict.rs

@@ -21,6 +21,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn try_report_named_anon_conflict(&self, error: &RegionResolutionError<'tcx>) -> bool {
         let (span, sub, sup) = match *error {
             ConcreteFailure(ref origin, sub, sup) => (origin.span(), sub, sup),
+            SubSupConflict(_, ref origin, sub, _, sup) => (origin.span(), sub, sup),
             _ => return false, // inapplicable
         };
 

src/librustc/infer/region_inference/graphviz.rs

@@ -30,6 +30,7 @@ use util::nodemap::{FxHashMap, FxHashSet};
 
 use std::borrow::Cow;
 use std::collections::hash_map::Entry::Vacant;
+use std::collections::btree_map::BTreeMap;
 use std::env;
 use std::fs::File;
 use std::io;
@@ -124,7 +125,7 @@ pub fn maybe_print_constraints_for<'a, 'gcx, 'tcx>(
 struct ConstraintGraph<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     graph_name: String,
     region_rels: &'a RegionRelations<'a, 'gcx, 'tcx>,
-    map: &'a FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
+    map: &'a BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
     node_ids: FxHashMap<Node, usize>,
 }
 
@@ -264,7 +265,7 @@ impl<'a, 'gcx, 'tcx> dot::GraphWalk<'a> for ConstraintGraph<'a, 'gcx, 'tcx> {
     }
 }
 
-pub type ConstraintMap<'tcx> = FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
+pub type ConstraintMap<'tcx> = BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
 
 fn dump_region_constraints_to<'a, 'gcx, 'tcx>(region_rels: &RegionRelations<'a, 'gcx, 'tcx>,
                                               map: &ConstraintMap<'tcx>,

src/librustc/infer/region_inference/mod.rs

@@ -28,6 +28,7 @@ use ty::{Region, RegionVid};
 use ty::{ReEmpty, ReStatic, ReFree, ReEarlyBound, ReErased};
 use ty::{ReLateBound, ReScope, ReVar, ReSkolemized, BrFresh};
 
+use std::collections::BTreeMap;
 use std::cell::{Cell, RefCell};
 use std::fmt;
 use std::mem;
@@ -36,7 +37,7 @@ use std::u32;
 mod graphviz;
 
 /// A constraint that influences the inference process.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub enum Constraint<'tcx> {
     /// One region variable is subregion of another
     ConstrainVarSubVar(RegionVid, RegionVid),
@@ -186,7 +187,13 @@ pub struct RegionVarBindings<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     /// Constraints of the form `A <= B` introduced by the region
     /// checker.  Here at least one of `A` and `B` must be a region
     /// variable.
-    constraints: RefCell<FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>>,
+    ///
+    /// Using `BTreeMap` because the order in which we iterate over
+    /// these constraints can affect the way we build the region graph,
+    /// which in turn affects the way that region errors are reported,
+    /// leading to small variations in error output across runs and
+    /// platforms.
+    constraints: RefCell<BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>>,
 
     /// A "verify" is something that we need to verify after inference is
     /// done, but which does not directly affect inference in any way.
@@ -357,7 +364,7 @@ impl<'a, 'gcx, 'tcx> RegionVarBindings<'a, 'gcx, 'tcx> {
             tcx,
             var_origins: RefCell::new(Vec::new()),
             values: RefCell::new(None),
-            constraints: RefCell::new(FxHashMap()),
+            constraints: RefCell::new(BTreeMap::new()),
             verifys: RefCell::new(Vec::new()),
             givens: RefCell::new(FxHashSet()),
             lubs: RefCell::new(FxHashMap()),

src/librustc/ty/sty.rs

@@ -760,7 +760,7 @@ impl<'a, 'gcx, 'tcx> ParamTy {
 /// is the outer fn.
 ///
 /// [dbi]: http://en.wikipedia.org/wiki/De_Bruijn_index
-#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, Copy)]
+#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, Copy, PartialOrd, Ord)]
 pub struct DebruijnIndex {
     /// We maintain the invariant that this is never 0. So 1 indicates
     /// the innermost binder. To ensure this, create with `DebruijnIndex::new`.
@@ -825,7 +825,7 @@ pub type Region<'tcx> = &'tcx RegionKind;
 ///
 /// [1] http://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/
 /// [2] http://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/
-#[derive(Clone, PartialEq, Eq, Hash, Copy, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Eq, Hash, Copy, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
 pub enum RegionKind {
     // Region bound in a type or fn declaration which will be
     // substituted 'early' -- that is, at the same time when type
@@ -871,7 +871,7 @@ pub enum RegionKind {
 
 impl<'tcx> serialize::UseSpecializedDecodable for Region<'tcx> {}
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, PartialOrd, Ord)]
 pub struct EarlyBoundRegion {
     pub def_id: DefId,
     pub index: u32,
@@ -893,12 +893,12 @@ pub struct FloatVid {
     pub index: u32,
 }
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy)]
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy, PartialOrd, Ord)]
 pub struct RegionVid {
     pub index: u32,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
 pub struct SkolemizedRegionVid {
     pub index: u32,
 }

src/test/compile-fail/associated-types-project-from-hrtb-in-fn-body.rs

@@ -30,7 +30,7 @@ fn bar<'a, 'b, I : for<'x> Foo<&'x isize>>(
 {
     // x and y here have two distinct lifetimes:
     let z: I::A = if cond { x } else { y };
-    //~^ ERROR cannot infer
+    //~^ ERROR lifetime mismatch
 }
 
 pub fn main() {}

src/test/compile-fail/associated-types/cache/project-fn-ret-contravariant.rs

@@ -50,9 +50,10 @@ fn baz<'a,'b>(x: &'a u32) -> &'static u32 {
 
 #[cfg(krisskross)] // two instantiations, mixing and matching: BAD
 fn transmute<'a,'b>(x: &'a u32, y: &'b u32) -> (&'a u32, &'b u32) {
-   let a = bar(foo, y); //[krisskross]~ ERROR E0495
-   let b = bar(foo, x); //[krisskross]~ ERROR E0495
-   (a, b)
+   let a = bar(foo, y);
+   let b = bar(foo, x);
+   (a, b) //[krisskross]~ ERROR 55:5: 55:6: lifetime mismatch [E0623]
+   //[krisskross]~^ ERROR 55:8: 55:9: lifetime mismatch [E0623]
 }
 
 #[rustc_error]

src/test/compile-fail/associated-types/cache/project-fn-ret-invariant.rs

@@ -45,8 +45,8 @@ fn baz<'a,'b>(x: Type<'a>, y: Type<'b>) -> (Type<'a>, Type<'b>) {
 #[cfg(oneuse)] // one instantiation: BAD
 fn baz<'a,'b>(x: Type<'a>, y: Type<'b>) -> (Type<'a>, Type<'b>) {
    let f = foo; // <-- No consistent type can be inferred for `f` here.
-   let a = bar(f, x); //[oneuse]~^ ERROR E0495
-   let b = bar(f, y);
+   let a = bar(f, x);
+   let b = bar(f, y); //[oneuse]~ ERROR 49:19: 49:20: lifetime mismatch [E0623]
    (a, b)
 }
 
@@ -60,9 +60,9 @@ fn baz<'a,'b>(x: Type<'a>) -> Type<'static> {
 
 #[cfg(krisskross)] // two instantiations, mixing and matching: BAD
 fn transmute<'a,'b>(x: Type<'a>, y: Type<'b>) -> (Type<'a>, Type<'b>) {
-   let a = bar(foo, y); //[krisskross]~ ERROR E0495
-   let b = bar(foo, x); //[krisskross]~ ERROR E0495
-   (a, b)
+   let a = bar(foo, y); //[krisskross]~ ERROR E0623
+   let b = bar(foo, x);
+   (a, b) //[krisskross]~ ERROR E0623
 }
 
 #[rustc_error]

src/test/compile-fail/borrowck/borrowck-reborrow-from-shorter-lived-andmut.rs

@@ -17,7 +17,7 @@ struct S<'a> {
 
 fn copy_borrowed_ptr<'a,'b>(p: &'a mut S<'b>) -> S<'b> {
     S { pointer: &mut *p.pointer }
-    //~^ ERROR cannot infer
+    //~^ ERROR lifetime mismatch
 }
 
 fn main() {

src/test/compile-fail/issue-13058.rs

@@ -22,7 +22,7 @@ impl<'r> Itble<'r, usize, Range<usize>> for (usize, usize) {
 fn check<'r, I: Iterator<Item=usize>, T: Itble<'r, usize, I>>(cont: &T) -> bool
 {
     let cont_iter = cont.iter();
-//~^ ERROR cannot infer an appropriate lifetime for autoref due to conflicting requirements
+//~^ ERROR 24:26: 24:30: explicit lifetime required in the type of `cont` [E0621]
     let result = cont_iter.fold(Some(0), |state, val| {
         state.map_or(None, |mask| {
             let bit = 1 << val;