fix corner case in if_return (#5711)

fixes #5710

Author: alexlamsl

Diff for: lib/compress.js

@@ -3536,7 +3536,7 @@ Compressor.prototype.compress = function(node) {
             var declare_only, jump, merge_jump;
             var in_iife = in_lambda && parent && parent.TYPE == "Call" && parent.expression === self;
             var chain_if_returns = in_lambda && compressor.option("conditionals") && compressor.option("sequences");
-            var drop_return_void = !(in_try && in_try.bfinally && in_async_generator(in_lambda));
+            var drop_return_void = !(in_try && in_try.bfinally && in_async_generator(scope));
             var multiple_if_returns = has_multiple_if_returns(statements);
             for (var i = statements.length; --i >= 0;) {
                 var stat = statements[i];

Diff for: test/compress/yields.js

@@ -2039,3 +2039,40 @@ issue_5707: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5710: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        (async function*() {
+            try {
+                switch (42) {
+                  case 42:
+                    {
+                        if (console.log("PASS"))
+                            return;
+                        return null;
+                    }
+                    break;
+                }
+            } finally {}
+        })().next();
+    }
+    expect: {
+        (async function*() {
+            try {
+                switch (42) {
+                  case 42:
+                    if (console.log("PASS"))
+                        return;
+                    return null;
+                    break;
+                }
+            } finally {}
+        })().next();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=10"
+}