fix corner case in `mangle` (#4528)

fixes #4527

2 files changed, 36 insertions, 0 deletions

diff --git a/lib/scope.js b/lib/scope.js
index ea662815..f4a18ca7 100644
--- a/lib/scope.js
+++ b/lib/scope.js
@@ -611,6 +611,7 @@ AST_Toplevel.DEFMETHOD("mangle_names", function(options) {
             if (!(sym instanceof AST_SymbolConst)) return false;
             var scope = def.scope.resolve();
             if (def.scope === scope) return false;
+            if (def.scope.parent_scope.find_variable(sym.name)) return false;
             redef = scope.def_variable(sym);
             scope.to_mangle.push(redef);
         }
diff --git a/test/compress/const.js b/test/compress/const.js
index 0281fd87..38cd8fbd 100644
--- a/test/compress/const.js
+++ b/test/compress/const.js
@@ -1399,3 +1399,38 @@ issue_4365_2: {
     }
     expect_stdout: true
 }
+
+issue_4527: {
+    mangle = {}
+    input: {
+        (function() {
+            try {
+                throw 1;
+            } catch (a) {
+                try {
+                    const a = FAIL;
+                } finally {
+                    if (!b)
+                        return console.log("aaaa");
+                }
+            }
+            var b;
+        })();
+    }
+    expect: {
+        (function() {
+            try {
+                throw 1;
+            } catch (a) {
+                try {
+                    const a = FAIL;
+                } finally {
+                    if (!t)
+                        return console.log("aaaa");
+                }
+            }
+            var t;
+        })();
+    }
+    expect_stdout: "aaaa"
+}