Fix panic in const eval and parameter destructing

6 files changed, 57 insertions, 17 deletions

diff --git a/crates/hir-ty/src/mir.rs b/crates/hir-ty/src/mir.rs
index d830ae263ba..6d8e73655ed 100644
--- a/crates/hir-ty/src/mir.rs
+++ b/crates/hir-ty/src/mir.rs
@@ -714,13 +714,8 @@ pub enum Rvalue {
 
     /// Creates an array where each element is the value of the operand.
     ///
-    /// This is the cause of a bug in the case where the repetition count is zero because the value
-    /// is not dropped, see [#74836].
-    ///
     /// Corresponds to source code like `[x; 32]`.
-    ///
-    /// [#74836]: https://github.com/rust-lang/rust/issues/74836
-    //Repeat(Operand, ty::Const),
+    Repeat(Operand, Const),
 
     /// Creates a reference of the indicated kind to the place.
     ///
@@ -932,6 +927,7 @@ impl MirBody {
                             Rvalue::ShallowInitBox(o, _)
                             | Rvalue::UnaryOp(_, o)
                             | Rvalue::Cast(_, o, _)
+                            | Rvalue::Repeat(o, _)
                             | Rvalue::Use(o) => for_operand(o, &mut f),
                             Rvalue::CopyForDeref(p)
                             | Rvalue::Discriminant(p)
diff --git a/crates/hir-ty/src/mir/eval.rs b/crates/hir-ty/src/mir/eval.rs
index 218aab93f12..bb33da97e33 100644
--- a/crates/hir-ty/src/mir/eval.rs
+++ b/crates/hir-ty/src/mir/eval.rs
@@ -769,6 +769,7 @@ impl Evaluator<'_> {
                     }
                 }
             }
+            Rvalue::Repeat(_, _) => not_supported!("evaluating repeat rvalue"),
             Rvalue::ShallowInitBox(_, _) => not_supported!("shallow init box"),
             Rvalue::CopyForDeref(_) => not_supported!("copy for deref"),
             Rvalue::Aggregate(kind, values) => {
diff --git a/crates/hir-ty/src/mir/lower.rs b/crates/hir-ty/src/mir/lower.rs
index 687b9835f57..37b27b39834 100644
--- a/crates/hir-ty/src/mir/lower.rs
+++ b/crates/hir-ty/src/mir/lower.rs
@@ -964,7 +964,22 @@ impl<'ctx> MirLowerCtx<'ctx> {
                     self.push_assignment(current, place, r, expr_id.into());
                     Ok(Some(current))
                 }
-                Array::Repeat { .. } => not_supported!("array repeat"),
+                Array::Repeat { initializer, .. } => {
+                    let Some((init, current)) = self.lower_expr_to_some_operand(*initializer, current)? else {
+                        return Ok(None);
+                    };
+                    let len = match &self.expr_ty(expr_id).data(Interner).kind {
+                        TyKind::Array(_, len) => len.clone(),
+                        _ => {
+                            return Err(MirLowerError::TypeError(
+                                "Array repeat expression with non array type",
+                            ))
+                        }
+                    };
+                    let r = Rvalue::Repeat(init, len);
+                    self.push_assignment(current, place, r, expr_id.into());
+                    Ok(Some(current))
+                },
             },
             Expr::Literal(l) => {
                 let ty = self.expr_ty(expr_id);
@@ -1433,7 +1448,12 @@ impl<'ctx> MirLowerCtx<'ctx> {
     fn binding_local(&self, b: BindingId) -> Result<LocalId> {
         match self.result.binding_locals.get(b) {
             Some(x) => Ok(*x),
-            None => Err(MirLowerError::UnaccessableLocal),
+            None => {
+                // FIXME: It should never happens, but currently it will happen in `const_dependent_on_local` test, which
+                // is a hir lowering problem IMO.
+                // never!("Using unaccessable local for binding is always a bug");
+                Err(MirLowerError::UnaccessableLocal)
+            }
         }
     }
 }
@@ -1588,14 +1608,23 @@ pub fn lower_to_mir(
         }
     };
     // 1 to param_len is for params
-    let current = if let DefWithBodyId::FunctionId(fid) = owner {
-        let substs = TyBuilder::placeholder_subst(db, fid);
-        let callable_sig = db.callable_item_signature(fid.into()).substitute(Interner, &substs);
-        ctx.lower_params_and_bindings(
-            body.params.iter().zip(callable_sig.params().iter()).map(|(x, y)| (*x, y.clone())),
-            binding_picker,
-        )?
-    } else {
+    // FIXME: replace with let chain once it becomes stable
+    let current = 'b: {
+        if body.body_expr == root_expr {
+            // otherwise it's an inline const, and has no parameter
+            if let DefWithBodyId::FunctionId(fid) = owner {
+                let substs = TyBuilder::placeholder_subst(db, fid);
+                let callable_sig =
+                    db.callable_item_signature(fid.into()).substitute(Interner, &substs);
+                break 'b ctx.lower_params_and_bindings(
+                    body.params
+                        .iter()
+                        .zip(callable_sig.params().iter())
+                        .map(|(x, y)| (*x, y.clone())),
+                    binding_picker,
+                )?;
+            }
+        }
         ctx.lower_params_and_bindings([].into_iter(), binding_picker)?
     };
     if let Some(b) = ctx.lower_expr_to_place(root_expr, return_slot().into(), current)? {
diff --git a/crates/hir-ty/src/mir/lower/pattern_matching.rs b/crates/hir-ty/src/mir/lower/pattern_matching.rs
index a5b48b6b936..86c3ce9eec9 100644
--- a/crates/hir-ty/src/mir/lower/pattern_matching.rs
+++ b/crates/hir-ty/src/mir/lower/pattern_matching.rs
@@ -129,7 +129,7 @@ impl MirLowerCtx<'_> {
                 _ => not_supported!("expression path literal"),
             },
             Pat::Bind { id, subpat } => {
-                let target_place = self.result.binding_locals[*id];
+                let target_place = self.binding_local(*id)?;
                 let mode = self.body.bindings[*id].mode;
                 if let Some(subpat) = subpat {
                     (current, current_else) = self.pattern_match(
diff --git a/crates/hir-ty/src/mir/pretty.rs b/crates/hir-ty/src/mir/pretty.rs
index 3e1f2ecef1b..a7dff396135 100644
--- a/crates/hir-ty/src/mir/pretty.rs
+++ b/crates/hir-ty/src/mir/pretty.rs
@@ -321,6 +321,11 @@ impl<'a> MirPrettyCtx<'a> {
                 self.operand_list(x);
                 w!(self, "]");
             }
+            Rvalue::Repeat(op, len) => {
+                w!(self, "[");
+                self.operand(op);
+                w!(self, "; {}]", len.display(self.db));
+            }
             Rvalue::Aggregate(AggregateKind::Adt(_, _), x) => {
                 w!(self, "Adt(");
                 self.operand_list(x);
diff --git a/crates/ide-diagnostics/src/handlers/mutability_errors.rs b/crates/ide-diagnostics/src/handlers/mutability_errors.rs
index 9184125286a..d60007b48a6 100644
--- a/crates/ide-diagnostics/src/handlers/mutability_errors.rs
+++ b/crates/ide-diagnostics/src/handlers/mutability_errors.rs
@@ -546,6 +546,15 @@ fn f(x: i32) {
 }
 "#,
         );
+        check_diagnostics(
+            r#"
+fn f((x, y): (i32, i32)) {
+    let t = [0; 2];
+   x = 5;
+ //^^^^^ 💡 error: cannot mutate immutable variable `x`
+}
+"#,
+        );
     }
 
     #[test]