Use full expr span for return suggestion on type error/ambiguity

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2042,7 +2042,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                     if block_num > 1 && found_semi {
                         err.span_suggestion_verbose(
-                            span.shrink_to_lo(),
+                            // use the span of the *whole* expr
+                            self.tcx.hir().span(binding_hir_id).shrink_to_lo(),
                             "you might have meant to return this to infer its type parameters",
                             "return ",
                             Applicability::MaybeIncorrect,

tests/ui/return/tail-expr-as-potential-return.rs

@@ -45,3 +45,19 @@ async fn foo2() -> i32 {
     }
     0
 }
+
+struct Receiver;
+impl Receiver {
+    fn generic<T>(self) -> Option<T> {
+        None
+    }
+}
+fn method() -> Option<i32> {
+    if true {
+        Receiver.generic();
+        //~^ ERROR type annotations needed
+        //| HELP you might have meant to return this value
+    }
+
+    None
+}

tests/ui/return/tail-expr-as-potential-return.stderr

@@ -47,6 +47,22 @@ help: you might have meant to return this value
 LL |         return Err(42);
    |         ++++++        +
 
-error: aborting due to 3 previous errors
+error[E0282]: type annotations needed
+  --> $DIR/tail-expr-as-potential-return.rs:57:18
+   |
+LL |         Receiver.generic();
+   |                  ^^^^^^^ cannot infer type of the type parameter `T` declared on the method `generic`
+   |
+help: consider specifying the generic argument
+   |
+LL |         Receiver.generic::<T>();
+   |                         +++++
+help: you might have meant to return this to infer its type parameters
+   |
+LL |         return Receiver.generic();
+   |         ++++++
+
+error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0282, E0308.
+For more information about an error, try `rustc --explain E0282`.