Properly compare types for Option::as_deref suggestion

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -3593,7 +3593,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             && let Some(deref_target_did) = tcx.lang_items().deref_target()
             && let projection = tcx.mk_projection(deref_target_did, tcx.mk_substs(&[ty::GenericArg::from(found_ty)]))
             && let Ok(deref_target) = tcx.try_normalize_erasing_regions(param_env, projection)
-            && deref_target == target_ty
+            && infcx.can_eq(param_env, deref_target, target_ty)
         {
             let help = if let hir::Mutability::Mut = needs_mut
                 && let Some(deref_mut_did) = tcx.lang_items().deref_mut_trait()

tests/ui/mismatched_types/suggest-option-asderef-unfixable.rs

@@ -10,10 +10,6 @@ fn no_args() -> Option<()> {
     Some(())
 }
 
-fn generic_ref<T>(_: &T) -> Option<()> {
-    Some(())
-}
-
 extern "C" fn takes_str_but_wrong_abi(_: &str) -> Option<()> {
     Some(())
 }
@@ -33,8 +29,6 @@ fn main() {
     //~^ ERROR expected a `FnOnce<(String,)>` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
     let _ = produces_string().and_then(no_args);
     //~^ ERROR function is expected to take 1 argument, but it takes 0 arguments
-    let _ = produces_string().and_then(generic_ref);
-    //~^ ERROR type mismatch in function arguments
     let _ = Some(TypeWithoutDeref).and_then(takes_str_but_too_many_refs);
     //~^ ERROR type mismatch in function arguments
 }

tests/ui/mismatched_types/suggest-option-asderef-unfixable.stderr

@@ -1,5 +1,5 @@
 error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef-unfixable.rs:28:40
+  --> $DIR/suggest-option-asderef-unfixable.rs:24:40
    |
 LL | fn takes_str_but_too_many_refs(_: &&str) -> Option<()> {
    | ------------------------------------------------------ found signature defined here
@@ -15,7 +15,7 @@ note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
 error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
-  --> $DIR/suggest-option-asderef-unfixable.rs:30:40
+  --> $DIR/suggest-option-asderef-unfixable.rs:26:40
    |
 LL |     let _ = produces_string().and_then(takes_str_but_wrong_abi);
    |                               -------- ^^^^^^^^^^^^^^^^^^^^^^^ expected an `FnOnce<(String,)>` closure, found `for<'a> extern "C" fn(&'a str) -> Option<()> {takes_str_but_wrong_abi}`
@@ -27,7 +27,7 @@ note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
 error[E0277]: expected a `FnOnce<(String,)>` closure, found `for<'a> unsafe fn(&'a str) -> Option<()> {takes_str_but_unsafe}`
-  --> $DIR/suggest-option-asderef-unfixable.rs:32:40
+  --> $DIR/suggest-option-asderef-unfixable.rs:28:40
    |
 LL |     let _ = produces_string().and_then(takes_str_but_unsafe);
    |                               -------- ^^^^^^^^^^^^^^^^^^^^ call the function in a closure: `|| unsafe { /* code */ }`
@@ -40,7 +40,7 @@ note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
 error[E0593]: function is expected to take 1 argument, but it takes 0 arguments
-  --> $DIR/suggest-option-asderef-unfixable.rs:34:40
+  --> $DIR/suggest-option-asderef-unfixable.rs:30:40
    |
 LL | fn no_args() -> Option<()> {
    | -------------------------- takes 0 arguments
@@ -54,28 +54,7 @@ note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
 error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef-unfixable.rs:36:40
+  --> $DIR/suggest-option-asderef-unfixable.rs:32:45
-   |
-LL | fn generic_ref<T>(_: &T) -> Option<()> {
-   | -------------------------------------- found signature defined here
-...
-LL |     let _ = produces_string().and_then(generic_ref);
-   |                               -------- ^^^^^^^^^^^ expected due to this
-   |                               |
-   |                               required by a bound introduced by this call
-   |
-   = note: expected function signature `fn(String) -> _`
-              found function signature `for<'a> fn(&'a _) -> _`
-note: required by a bound in `Option::<T>::and_then`
-  --> $SRC_DIR/core/src/option.rs:LL:COL
-help: do not borrow the argument
-   |
-LL - fn generic_ref<T>(_: &T) -> Option<()> {
-LL + fn generic_ref<T>(_: T) -> Option<()> {
-   |
-
-error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef-unfixable.rs:38:45
    |
 LL | fn takes_str_but_too_many_refs(_: &&str) -> Option<()> {
    | ------------------------------------------------------ found signature defined here
@@ -90,7 +69,7 @@ LL |     let _ = Some(TypeWithoutDeref).and_then(takes_str_but_too_many_refs);
 note: required by a bound in `Option::<T>::and_then`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0277, E0593, E0631.
 For more information about an error, try `rustc --explain E0277`.

tests/ui/mismatched_types/suggest-option-asderef.fixed

@@ -16,6 +16,11 @@ fn generic<T>(_: T) -> Option<()> {
     Some(())
 }
 
+fn generic_ref<T>(_: T) -> Option<()> {
+    //~^ HELP do not borrow the argument
+    Some(())
+}
+
 fn main() {
     let _: Option<()> = produces_string().as_deref().and_then(takes_str);
     //~^ ERROR type mismatch in function arguments
@@ -27,4 +32,8 @@ fn main() {
     //~^ ERROR type mismatch in function arguments
     //~| HELP call `Option::as_deref_mut()` first
     let _ = produces_string().and_then(generic);
+
+    let _ = produces_string().as_deref().and_then(generic_ref);
+    //~^ ERROR type mismatch in function arguments
+    //~| HELP call `Option::as_deref()` first
 }

tests/ui/mismatched_types/suggest-option-asderef.rs

@@ -16,6 +16,11 @@ fn generic<T>(_: T) -> Option<()> {
     Some(())
 }
 
+fn generic_ref<T>(_: &T) -> Option<()> {
+    //~^ HELP do not borrow the argument
+    Some(())
+}
+
 fn main() {
     let _: Option<()> = produces_string().and_then(takes_str);
     //~^ ERROR type mismatch in function arguments
@@ -27,4 +32,8 @@ fn main() {
     //~^ ERROR type mismatch in function arguments
     //~| HELP call `Option::as_deref_mut()` first
     let _ = produces_string().and_then(generic);
+
+    let _ = produces_string().and_then(generic_ref);
+    //~^ ERROR type mismatch in function arguments
+    //~| HELP call `Option::as_deref()` first
 }

tests/ui/mismatched_types/suggest-option-asderef.stderr

@@ -1,5 +1,5 @@
 error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef.rs:20:52
+  --> $DIR/suggest-option-asderef.rs:25:52
    |
 LL | fn takes_str(_: &str) -> Option<()> {
    | ----------------------------------- found signature defined here
@@ -19,7 +19,7 @@ LL |     let _: Option<()> = produces_string().as_deref().and_then(takes_str);
    |                                          +++++++++++
 
 error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef.rs:23:55
+  --> $DIR/suggest-option-asderef.rs:28:55
    |
 LL | fn takes_str(_: &str) -> Option<()> {
    | ----------------------------------- found signature defined here
@@ -39,7 +39,7 @@ LL |     let _: Option<Option<()>> = produces_string().as_deref().map(takes_str)
    |                                                  +++++++++++
 
 error[E0631]: type mismatch in function arguments
-  --> $DIR/suggest-option-asderef.rs:26:55
+  --> $DIR/suggest-option-asderef.rs:31:55
    |
 LL | fn takes_str_mut(_: &mut str) -> Option<()> {
    | ------------------------------------------- found signature defined here
@@ -58,6 +58,31 @@ help: call `Option::as_deref_mut()` first
 LL |     let _: Option<Option<()>> = produces_string().as_deref_mut().map(takes_str_mut);
    |                                                  +++++++++++++++
 
-error: aborting due to 3 previous errors
+error[E0631]: type mismatch in function arguments
+  --> $DIR/suggest-option-asderef.rs:36:40
+   |
+LL | fn generic_ref<T>(_: &T) -> Option<()> {
+   | -------------------------------------- found signature defined here
+...
+LL |     let _ = produces_string().and_then(generic_ref);
+   |                               -------- ^^^^^^^^^^^ expected due to this
+   |                               |
+   |                               required by a bound introduced by this call
+   |
+   = note: expected function signature `fn(String) -> _`
+              found function signature `for<'a> fn(&'a _) -> _`
+note: required by a bound in `Option::<T>::and_then`
+  --> $SRC_DIR/core/src/option.rs:LL:COL
+help: do not borrow the argument
+   |
+LL - fn generic_ref<T>(_: &T) -> Option<()> {
+LL + fn generic_ref<T>(_: T) -> Option<()> {
+   |
+help: call `Option::as_deref()` first
+   |
+LL |     let _ = produces_string().as_deref().and_then(generic_ref);
+   |                              +++++++++++
+
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0631`.