Check whether the next_node is else-less if in get_return_block

compiler/rustc_middle/src/hir/map/mod.rs

@@ -549,6 +549,7 @@ impl<'hir> Map<'hir> {
                     Node::Block(Block { expr: None, .. }) => return None,
                     // The current node is not the tail expression of its parent.
                     Node::Block(Block { expr: Some(e), .. }) if hir_id != e.hir_id => return None,
+                    Node::Block(Block { expr: Some(e), ..}) if matches!(e.kind, ExprKind::If(_, _, None)) => return None,
                     _ => {}
                 }
             }

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

@@ -0,0 +1,5 @@
+fn main() {
+    if true {
+        "" //~ ERROR mismatched types [E0308]
+    }
+}

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

@@ -0,0 +1,12 @@
+error[E0308]: mismatched types
+  --> $DIR/tail-expr-if-as-return.rs:3:9
+   |
+LL | /     if true {
+LL | |         ""
+   | |         ^^ expected `()`, found `&str`
+LL | |     }
+   | |_____- expected this to be `()`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.