Rollup merge of #64679 - skinny121:const-infer, r=varkor

Infer consts more consistently

Moved some duplicated logic in `TypeRelation` methods into `super_combined_consts`. Before some `TypeRelation`s like `Lub` wasn't using `replace_if_possible`, meaning some inference types were staying around longer than they should be.

Fixes https://github.com/rust-lang/rust/issues/64519

r? @varkor

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/test/ui/const-generics/issue-64519.rs

@@ -0,0 +1,21 @@
+// check-pass
+
+#![feature(const_generics)]
+//~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
+
+struct Foo<const D: usize> {
+    state: Option<[u8; D]>,
+}
+
+impl<const D: usize> Iterator for Foo<{D}> {
+    type Item = [u8; D];
+    fn next(&mut self) -> Option<Self::Item> {
+        if true {
+            return Some(self.state.unwrap().clone());
+        } else {
+            return Some(self.state.unwrap().clone());
+        }
+    }
+}
+
+fn main() {}

src/test/ui/const-generics/issue-64519.stderr

@@ -0,0 +1,8 @@
+warning: the feature `const_generics` is incomplete and may cause the compiler to crash
+  --> $DIR/issue-64519.rs:3:12
+   |
+LL | #![feature(const_generics)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+