Fix circular fn_sig queries to return the correct number of arguments…

… for methods

compiler/rustc_middle/src/values.rs

@@ -56,7 +56,7 @@ impl<'tcx> Value<TyCtxt<'tcx>> for ty::Binder<'_, ty::FnSig<'_>> {
             && let Some(node) = tcx.hir().get_if_local(def_id)
             && let Some(sig) = node.fn_sig()
         {
-            sig.decl.inputs.len() + sig.decl.implicit_self.has_implicit_self() as usize
+            sig.decl.inputs.len()
         } else {
             tcx.dcx().abort_if_errors();
             unreachable!()

tests/ui/mismatched_types/mismatch-args-crash-issue-130400.rs

@@ -0,0 +1,8 @@
+trait Bar {
+    fn foo(&mut self) -> _ {
+        //~^ ERROR the placeholder `_` is not allowed within types on item signatures for return types
+        Self::foo() //~ ERROR  this function takes 1 argument but 0 arguments were supplied
+    }
+}
+
+fn main() {}

tests/ui/mismatched_types/mismatch-args-crash-issue-130400.stderr

@@ -0,0 +1,26 @@
+error[E0061]: this function takes 1 argument but 0 arguments were supplied
+  --> $DIR/mismatch-args-crash-issue-130400.rs:4:9
+   |
+LL |         Self::foo()
+   |         ^^^^^^^^^-- argument #1 is missing
+   |
+note: method defined here
+  --> $DIR/mismatch-args-crash-issue-130400.rs:2:8
+   |
+LL |     fn foo(&mut self) -> _ {
+   |        ^^^ ---------
+help: provide the argument
+   |
+LL |         Self::foo(/* value */)
+   |                  ~~~~~~~~~~~~~
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
+  --> $DIR/mismatch-args-crash-issue-130400.rs:2:26
+   |
+LL |     fn foo(&mut self) -> _ {
+   |                          ^ not allowed in type signatures
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0061, E0121.
+For more information about an error, try `rustc --explain E0061`.