Do not use make use of InferenceResult::has_errors flag for mir building

It generaly does not work as expected right now as we fallback type parameters to errors

Author: Veykril

crates/hir-ty/src/infer.rs

@@ -466,6 +466,9 @@ pub struct InferenceResult {
     pub type_of_for_iterator: FxHashMap<ExprId, Ty>,
     type_mismatches: FxHashMap<ExprOrPatId, TypeMismatch>,
     /// Whether there are any type-mismatching errors in the result.
+    // FIXME: This isn't as useful as initially thought due to us falling back placeholders to
+    // `TyKind::Error`.
+    // Which will then mark this field.
     pub(crate) has_errors: bool,
     /// Interned common types to return references to.
     // FIXME: Move this into `InferenceContext`

crates/hir-ty/src/mir/eval.rs

@@ -1202,7 +1202,7 @@ impl Evaluator<'_> {
                     ty = z.clone();
                     let size = if ty.is_str() {
                         if *op != BinOp::Eq {
-                            never!("Only eq is builtin for `str`");
+                            never!("Only `eq` is builtin for `str`");
                         }
                         let ls = from_bytes!(usize, &lc[self.ptr_size()..self.ptr_size() * 2]);
                         let rs = from_bytes!(usize, &rc[self.ptr_size()..self.ptr_size() * 2]);

crates/hir-ty/src/mir/lower.rs

@@ -2156,7 +2156,7 @@ pub fn lower_to_mir(
     // need to take this input explicitly.
     root_expr: ExprId,
 ) -> Result<MirBody> {
-    if infer.has_errors {
+    if infer.type_mismatches().next().is_some() {
         return Err(MirLowerError::HasErrors);
     }
     let mut ctx = MirLowerCtx::new(db, owner, body, infer);