Don't try to resolve methods on unknown types

Fixes #10454, and some type mismatches.

Author: flodiebold

crates/hir_ty/src/autoderef.rs

@@ -108,8 +108,13 @@ fn builtin_deref(ty: &Ty) -> Option<&Ty> {
 }
 
 fn deref_by_trait(table: &mut InferenceTable, ty: Ty) -> Option<Ty> {
-    let db = table.db;
     let _p = profile::span("deref_by_trait");
+    if table.resolve_ty_shallow(&ty).inference_var(Interner).is_some() {
+        // don't try to deref unknown variables
+        return None;
+    }
+
+    let db = table.db;
     let deref_trait = db
         .lang_item(table.trait_env.krate, SmolStr::new_inline("deref"))
         .and_then(|l| l.as_trait())?;

crates/hir_ty/src/method_resolution.rs

@@ -681,6 +681,11 @@ fn iterate_method_candidates_with_autoref(
     name: Option<&Name>,
     mut callback: &mut dyn FnMut(ReceiverAdjustments, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
+    if receiver_ty.value.is_general_var(Interner, &receiver_ty.binders) {
+        // don't try to resolve methods on unknown types
+        return ControlFlow::Continue(());
+    }
+
     iterate_method_candidates_by_receiver(
         receiver_ty,
         first_adjustment.clone(),

crates/hir_ty/src/tests/method_resolution.rs

@@ -2,7 +2,7 @@ use expect_test::expect;
 
 use crate::tests::check;
 
-use super::{check_infer, check_types};
+use super::{check_infer, check_no_mismatches, check_types};
 
 #[test]
 fn infer_slice_method() {
@@ -1697,3 +1697,56 @@ fn test() {
 "#,
     );
 }
+
+#[test]
+fn bad_inferred_reference_1() {
+    check_no_mismatches(
+        r#"
+//- minicore: sized
+pub trait Into<T>: Sized {
+    fn into(self) -> T;
+}
+impl<T> Into<T> for T {
+    fn into(self) -> T { self }
+}
+
+trait ExactSizeIterator {
+    fn len(&self) -> usize;
+}
+
+pub struct Foo;
+impl Foo {
+    fn len(&self) -> usize { 0 }
+}
+
+pub fn test(generic_args: impl Into<Foo>) {
+    let generic_args = generic_args.into();
+    generic_args.len();
+    let _: Foo = generic_args;
+}
+"#,
+    );
+}
+
+#[test]
+fn bad_inferred_reference_2() {
+    check_no_mismatches(
+        r#"
+//- minicore: deref
+trait ExactSizeIterator {
+    fn len(&self) -> usize;
+}
+
+pub struct Foo;
+impl Foo {
+    fn len(&self) -> usize { 0 }
+}
+
+pub fn test() {
+    let generic_args;
+    generic_args.len();
+    let _: Foo = generic_args;
+}
+"#,
+    );
+}