Auto merge of #64695 - Centril:rollup-t1xnl2c, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #64294 (Fix `Stdio::piped` example code and lint)
 - #64670 (Cleanup syntax::ext::build)
 - #64674 (Propagate `types.err` in locals further to avoid spurious knock-down errors)
 - #64676 (Parse assoc type bounds in generic params and provide custom diagnostic)
 - #64677 (remove outdated comment)
 - #64679 (Infer consts more consistently)
 - #64688 (Clarify the "since" tidy check)

Failed merges:

r? @ghost

src/librustc/infer/combine.rs

@@ -30,6 +30,7 @@ use super::sub::Sub;
 use super::type_variable::TypeVariableValue;
 use super::unify_key::{ConstVarValue, ConstVariableValue};
 use super::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
+use super::unify_key::replace_if_possible;
 
 use crate::hir::def_id::DefId;
 use crate::mir::interpret::ConstValue;
@@ -127,6 +128,12 @@ impl<'infcx, 'tcx> InferCtxt<'infcx, 'tcx> {
     where
         R: TypeRelation<'tcx>,
     {
+        debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
+        if a == b { return Ok(a); }
+
+        let a = replace_if_possible(self.const_unification_table.borrow_mut(), a);
+        let b = replace_if_possible(self.const_unification_table.borrow_mut(), b);
+
         let a_is_expected = relation.a_is_expected();
 
         match (a.val, b.val) {

src/librustc/infer/equate.rs

@@ -1,14 +1,12 @@
-use super::combine::{CombineFields, RelationDir, const_unification_error};
+use super::combine::{CombineFields, RelationDir};
 use super::Subtype;
 
 use crate::hir::def_id::DefId;
 
-use crate::ty::{self, Ty, TyCtxt, InferConst};
+use crate::ty::{self, Ty, TyCtxt};
 use crate::ty::TyVar;
 use crate::ty::subst::SubstsRef;
 use crate::ty::relate::{self, Relate, RelateResult, TypeRelation};
-use crate::mir::interpret::ConstValue;
-use crate::infer::unify_key::replace_if_possible;
 
 /// Ensures `a` is made equal to `b`. Returns `a` on success.
 pub struct Equate<'combine, 'infcx, 'tcx> {
@@ -108,39 +106,7 @@ impl TypeRelation<'tcx> for Equate<'combine, 'infcx, 'tcx> {
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
-        if a == b { return Ok(a); }
-
-        let infcx = self.fields.infcx;
-        let a = replace_if_possible(infcx.const_unification_table.borrow_mut(), a);
-        let b = replace_if_possible(infcx.const_unification_table.borrow_mut(), b);
-        let a_is_expected = self.a_is_expected();
-
-        match (a.val, b.val) {
-            (ConstValue::Infer(InferConst::Var(a_vid)),
-                ConstValue::Infer(InferConst::Var(b_vid))) => {
-                infcx.const_unification_table
-                    .borrow_mut()
-                    .unify_var_var(a_vid, b_vid)
-                    .map_err(|e| const_unification_error(a_is_expected, e))?;
-                return Ok(a);
-            }
-
-            (ConstValue::Infer(InferConst::Var(a_id)), _) => {
-                self.fields.infcx.unify_const_variable(a_is_expected, a_id, b)?;
-                return Ok(a);
-            }
-
-            (_, ConstValue::Infer(InferConst::Var(b_id))) => {
-                self.fields.infcx.unify_const_variable(!a_is_expected, b_id, a)?;
-                return Ok(a);
-            }
-
-            _ => {}
-        }
-
-        self.fields.infcx.super_combine_consts(self, a, b)?;
-        Ok(a)
+        self.fields.infcx.super_combine_consts(self, a, b)
     }
 
     fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)

src/librustc/infer/glb.rs

@@ -66,11 +66,6 @@ impl TypeRelation<'tcx> for Glb<'combine, 'infcx, 'tcx> {
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
-        if a == b {
-            return Ok(a);
-        }
-
         self.fields.infcx.super_combine_consts(self, a, b)
     }
 

src/librustc/infer/lub.rs

@@ -66,11 +66,6 @@ impl TypeRelation<'tcx> for Lub<'combine, 'infcx, 'tcx> {
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
-        if a == b {
-            return Ok(a);
-        }
-
         self.fields.infcx.super_combine_consts(self, a, b)
     }
 

src/librustc/infer/sub.rs

@@ -1,13 +1,11 @@
 use super::SubregionOrigin;
-use super::combine::{CombineFields, RelationDir, const_unification_error};
+use super::combine::{CombineFields, RelationDir};
 
 use crate::traits::Obligation;
-use crate::ty::{self, Ty, TyCtxt, InferConst};
+use crate::ty::{self, Ty, TyCtxt};
 use crate::ty::TyVar;
 use crate::ty::fold::TypeFoldable;
 use crate::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
-use crate::infer::unify_key::replace_if_possible;
-use crate::mir::interpret::ConstValue;
 use std::mem;
 
 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
@@ -142,41 +140,7 @@ impl TypeRelation<'tcx> for Sub<'combine, 'infcx, 'tcx> {
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
-        if a == b { return Ok(a); }
-
-        let infcx = self.fields.infcx;
-        let a = replace_if_possible(infcx.const_unification_table.borrow_mut(), a);
-        let b = replace_if_possible(infcx.const_unification_table.borrow_mut(), b);
-
-        // Consts can only be equal or unequal to each other: there's no subtyping
-        // relation, so we're just going to perform equating here instead.
-        let a_is_expected = self.a_is_expected();
-        match (a.val, b.val) {
-            (ConstValue::Infer(InferConst::Var(a_vid)),
-                ConstValue::Infer(InferConst::Var(b_vid))) => {
-                infcx.const_unification_table
-                    .borrow_mut()
-                    .unify_var_var(a_vid, b_vid)
-                    .map_err(|e| const_unification_error(a_is_expected, e))?;
-                return Ok(a);
-            }
-
-            (ConstValue::Infer(InferConst::Var(a_id)), _) => {
-                self.fields.infcx.unify_const_variable(a_is_expected, a_id, b)?;
-                return Ok(a);
-            }
-
-            (_, ConstValue::Infer(InferConst::Var(b_id))) => {
-                self.fields.infcx.unify_const_variable(!a_is_expected, b_id, a)?;
-                return Ok(a);
-            }
-
-            _ => {}
-        }
-
-        self.fields.infcx.super_combine_consts(self, a, b)?;
-        Ok(a)
+        self.fields.infcx.super_combine_consts(self, a, b)
     }
 
     fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)

src/librustc_mir/borrow_check/flows.rs

@@ -23,7 +23,6 @@ use std::rc::Rc;
 
 crate type PoloniusOutput = Output<RegionVid, BorrowIndex, LocationIndex, Local, MovePathIndex>;
 
-// (forced to be `pub` due to its use as an associated type below.)
 crate struct Flows<'b, 'tcx> {
     borrows: FlowAtLocation<'tcx, Borrows<'b, 'tcx>>,
     pub uninits: FlowAtLocation<'tcx, MaybeUninitializedPlaces<'b, 'tcx>>,

src/librustc_typeck/check/coercion.rs

@@ -163,7 +163,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
 
         // Just ignore error types.
         if a.references_error() || b.references_error() {
-            return success(vec![], b, vec![]);
+            return success(vec![], self.fcx.tcx.types.err, vec![]);
         }
 
         if a.is_never() {
@@ -821,7 +821,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let (adjustments, _) = self.register_infer_ok_obligations(ok);
         self.apply_adjustments(expr, adjustments);
-        Ok(target)
+        Ok(if expr_ty.references_error() {
+            self.tcx.types.err
+        } else {
+            target
+        })
     }
 
     /// Same as `try_coerce()`, but without side-effects.

src/librustc_typeck/check/mod.rs

@@ -153,7 +153,7 @@ use self::method::{MethodCallee, SelfSource};
 use self::TupleArgumentsFlag::*;
 
 /// The type of a local binding, including the revealed type for anon types.
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Debug)]
 pub struct LocalTy<'tcx> {
     decl_ty: Ty<'tcx>,
     revealed_ty: Ty<'tcx>
@@ -3822,15 +3822,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         if let Some(ref init) = local.init {
             let init_ty = self.check_decl_initializer(local, &init);
-            if init_ty.references_error() {
-                self.write_ty(local.hir_id, init_ty);
-            }
+            self.overwrite_local_ty_if_err(local, t, init_ty);
         }
 
         self.check_pat_top(&local.pat, t, None);
         let pat_ty = self.node_ty(local.pat.hir_id);
-        if pat_ty.references_error() {
-            self.write_ty(local.hir_id, pat_ty);
+        self.overwrite_local_ty_if_err(local, t, pat_ty);
+    }
+
+    fn overwrite_local_ty_if_err(&self, local: &'tcx hir::Local, decl_ty: Ty<'tcx>, ty: Ty<'tcx>) {
+        if ty.references_error() {
+            // Override the types everywhere with `types.err` to avoid knock down errors.
+            self.write_ty(local.hir_id, ty);
+            self.write_ty(local.pat.hir_id, ty);
+            let local_ty = LocalTy {
+                decl_ty,
+                revealed_ty: ty,
+            };
+            self.locals.borrow_mut().insert(local.hir_id, local_ty);
+            self.locals.borrow_mut().insert(local.pat.hir_id, local_ty);
         }
     }
 

src/libstd/process.rs

@@ -940,7 +940,7 @@ impl Stdio {
     /// }
     ///
     /// let output = child.wait_with_output().expect("Failed to read stdout");
-    /// assert_eq!(String::from_utf8_lossy(&output.stdout), "!dlrow ,olleH\n");
+    /// assert_eq!(String::from_utf8_lossy(&output.stdout), "!dlrow ,olleH");
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn piped() -> Stdio { Stdio(imp::Stdio::MakePipe) }