Rollup merge of #105292 - JulianKnodt:no_eager_commit, r=BoxyUwU

Change a commit_if_ok call to probe

Removes an over-eager `commit_if_ok` which makes inference worse.

I'm not entirely sure whether it's ok to remove the check that types are the same, because casting seems to cause equality checks with incorrect types?

Fixes #105037

r? ```@BoxyUwU```

10 files changed, 221 insertions, 16 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index f8efe9bfa9f..71fb6058cd2 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -168,24 +168,27 @@ fn satisfied_from_param_env<'tcx>(
         param_env: ty::ParamEnv<'tcx>,
 
         infcx: &'a InferCtxt<'tcx>,
+        single_match: Option<Result<ty::Const<'tcx>, ()>>,
     }
+
     impl<'a, 'tcx> TypeVisitor<'tcx> for Visitor<'a, 'tcx> {
         type BreakTy = ();
         fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             debug!("is_const_evaluatable: candidate={:?}", c);
-            if let Ok(()) = self.infcx.commit_if_ok(|_| {
+            if self.infcx.probe(|_| {
                 let ocx = ObligationCtxt::new_in_snapshot(self.infcx);
-                if let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c.ty(), self.ct.ty())
-                    && let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c, self.ct)
+                ocx.eq(&ObligationCause::dummy(), self.param_env, c.ty(), self.ct.ty()).is_ok()
+                    && ocx.eq(&ObligationCause::dummy(), self.param_env, c, self.ct).is_ok()
                     && ocx.select_all_or_error().is_empty()
-                {
-                    Ok(())
-                } else {
-                    Err(())
-                }
             }) {
-                ControlFlow::BREAK
-            } else if let ty::ConstKind::Expr(e) = c.kind() {
+                self.single_match = match self.single_match {
+                    None => Some(Ok(c)),
+                    Some(Ok(o)) if o == c => Some(Ok(c)),
+                    Some(_) => Some(Err(())),
+                };
+            }
+
+            if let ty::ConstKind::Expr(e) = c.kind() {
                 e.visit_with(self)
             } else {
                 // FIXME(generic_const_exprs): This doesn't recurse into `<T as Trait<U>>::ASSOC`'s substs.
@@ -200,22 +203,29 @@ fn satisfied_from_param_env<'tcx>(
         }
     }
 
+    let mut single_match: Option<Result<ty::Const<'tcx>, ()>> = None;
+
     for pred in param_env.caller_bounds() {
         match pred.kind().skip_binder() {
             ty::PredicateKind::ConstEvaluatable(ce) => {
                 let b_ct = tcx.expand_abstract_consts(ce);
-                let mut v = Visitor { ct, infcx, param_env };
-                let result = b_ct.visit_with(&mut v);
+                let mut v = Visitor { ct, infcx, param_env, single_match };
+                let _ = b_ct.visit_with(&mut v);
 
-                if let ControlFlow::Break(()) = result {
-                    debug!("is_const_evaluatable: yes");
-                    return true;
-                }
+                single_match = v.single_match;
             }
             _ => {} // don't care
         }
     }
 
+    if let Some(Ok(c)) = single_match {
+        let ocx = ObligationCtxt::new(infcx);
+        assert!(ocx.eq(&ObligationCause::dummy(), param_env, c.ty(), ct.ty()).is_ok());
+        assert!(ocx.eq(&ObligationCause::dummy(), param_env, c, ct).is_ok());
+        assert!(ocx.select_all_or_error().is_empty());
+        return true;
+    }
+
     debug!("is_const_evaluatable: no");
     false
 }
diff --git a/src/test/ui/const-generics/ensure_is_evaluatable.rs b/src/test/ui/const-generics/ensure_is_evaluatable.rs
new file mode 100644
index 00000000000..1e8d8c3d355
--- /dev/null
+++ b/src/test/ui/const-generics/ensure_is_evaluatable.rs
@@ -0,0 +1,20 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn foo<const N: usize, const M: usize>() -> [(); N+2]
+where
+    [(); N + 1]:,
+    [(); M + 1]:,
+{
+    bar()
+    //~^ ERROR: unconstrained
+}
+
+fn bar<const N: usize>() -> [(); N]
+where
+    [(); N + 1]:,
+{
+    [(); N]
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/ensure_is_evaluatable.stderr b/src/test/ui/const-generics/ensure_is_evaluatable.stderr
new file mode 100644
index 00000000000..bf6c35ad8fd
--- /dev/null
+++ b/src/test/ui/const-generics/ensure_is_evaluatable.stderr
@@ -0,0 +1,18 @@
+error: unconstrained generic constant
+  --> $DIR/ensure_is_evaluatable.rs:9:5
+   |
+LL |     bar()
+   |     ^^^
+   |
+   = help: try adding a `where` bound using this expression: `where [(); N + 1]:`
+note: required by a bound in `bar`
+  --> $DIR/ensure_is_evaluatable.rs:15:10
+   |
+LL | fn bar<const N: usize>() -> [(); N]
+   |    --- required by a bound in this
+LL | where
+LL |     [(); N + 1]:,
+   |          ^^^^^ required by this bound in `bar`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/const-generics/fn_with_two_const_inputs.rs b/src/test/ui/const-generics/fn_with_two_const_inputs.rs
new file mode 100644
index 00000000000..0d6246a9f02
--- /dev/null
+++ b/src/test/ui/const-generics/fn_with_two_const_inputs.rs
@@ -0,0 +1,23 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+const fn both(_: usize, b: usize) -> usize {
+    b
+}
+
+fn foo<const N: usize, const M: usize>() -> [(); N + 2]
+where
+    [(); both(N + 1, M + 1)]:,
+{
+    bar()
+    //~^ ERROR: unconstrained generic constant
+}
+
+fn bar<const N: usize>() -> [(); N]
+where
+    [(); N + 1]:,
+{
+    [(); N]
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/fn_with_two_const_inputs.stderr b/src/test/ui/const-generics/fn_with_two_const_inputs.stderr
new file mode 100644
index 00000000000..614e7e0d2fc
--- /dev/null
+++ b/src/test/ui/const-generics/fn_with_two_const_inputs.stderr
@@ -0,0 +1,18 @@
+error: unconstrained generic constant
+  --> $DIR/fn_with_two_const_inputs.rs:12:5
+   |
+LL |     bar()
+   |     ^^^
+   |
+   = help: try adding a `where` bound using this expression: `where [(); N + 1]:`
+note: required by a bound in `bar`
+  --> $DIR/fn_with_two_const_inputs.rs:18:10
+   |
+LL | fn bar<const N: usize>() -> [(); N]
+   |    --- required by a bound in this
+LL | where
+LL |     [(); N + 1]:,
+   |          ^^^^^ required by this bound in `bar`
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/const-generics/fn_with_two_same_const_inputs.rs b/src/test/ui/const-generics/fn_with_two_same_const_inputs.rs
new file mode 100644
index 00000000000..f0ce093e07a
--- /dev/null
+++ b/src/test/ui/const-generics/fn_with_two_same_const_inputs.rs
@@ -0,0 +1,22 @@
+// check-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+const fn both(_: usize, b: usize) -> usize {
+    b
+}
+
+fn foo<const N: usize>()
+where
+    [(); both(N + 1, N + 1)]:,
+{
+    bar::<N>();
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/issues/issue-105037.rs b/src/test/ui/const-generics/issues/issue-105037.rs
new file mode 100644
index 00000000000..f7d23949943
--- /dev/null
+++ b/src/test/ui/const-generics/issues/issue-105037.rs
@@ -0,0 +1,35 @@
+// run-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+#![allow(dead_code)]
+
+trait Table<const D: usize>: Sync {
+    const COLUMNS: usize;
+}
+
+struct Table1<const D: usize>;
+impl<const D: usize> Table<D> for Table1<D> {
+    const COLUMNS: usize = 123;
+}
+
+struct Table2<const D: usize>;
+impl<const D: usize> Table<D> for Table2<D> {
+    const COLUMNS: usize = 456;
+}
+
+fn process_table<T: Table<D>, const D: usize>(_table: T)
+where
+    [(); T::COLUMNS]:,
+{
+}
+
+fn process_all_tables<const D: usize>()
+where
+    [(); Table2::<D>::COLUMNS]:,
+    [(); Table1::<D>::COLUMNS]:,
+{
+    process_table(Table1::<D>);
+    process_table(Table2::<D>);
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/two_matching_preds.rs b/src/test/ui/const-generics/two_matching_preds.rs
new file mode 100644
index 00000000000..de608f73e2c
--- /dev/null
+++ b/src/test/ui/const-generics/two_matching_preds.rs
@@ -0,0 +1,19 @@
+// check-pass
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn foo<const N: usize>()
+where
+    [(); N + 1]:,
+    [(); N + 1]:,
+{
+    bar::<N>();
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/unify_with_nested_expr.rs b/src/test/ui/const-generics/unify_with_nested_expr.rs
new file mode 100644
index 00000000000..1271e0902a3
--- /dev/null
+++ b/src/test/ui/const-generics/unify_with_nested_expr.rs
@@ -0,0 +1,18 @@
+#![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
+fn foo<const N: usize>()
+where
+    [(); N + 1 + 1]:,
+{
+    bar();
+    //~^ ERROR: type annotations
+}
+
+fn bar<const N: usize>()
+where
+    [(); N + 1]:,
+{
+}
+
+fn main() {}
diff --git a/src/test/ui/const-generics/unify_with_nested_expr.stderr b/src/test/ui/const-generics/unify_with_nested_expr.stderr
new file mode 100644
index 00000000000..8bab0dff7f2
--- /dev/null
+++ b/src/test/ui/const-generics/unify_with_nested_expr.stderr
@@ -0,0 +1,22 @@
+error[E0284]: type annotations needed
+  --> $DIR/unify_with_nested_expr.rs:8:5
+   |
+LL |     bar();
+   |     ^^^ cannot infer the value of the const parameter `N` declared on the function `bar`
+   |
+note: required by a bound in `bar`
+  --> $DIR/unify_with_nested_expr.rs:14:10
+   |
+LL | fn bar<const N: usize>()
+   |    --- required by a bound in this
+LL | where
+LL |     [(); N + 1]:,
+   |          ^^^^^ required by this bound in `bar`
+help: consider specifying the generic argument
+   |
+LL |     bar::<N>();
+   |        +++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0284`.