fix corner case in unused (#4236)

fixes #4235

lib/compress.js

@@ -4774,9 +4774,11 @@ merge(Compressor.prototype, {
                     node.definitions.forEach(function(defn) {
                         var def = defn.name.definition();
                         var_defs_by_id.add(def.id, defn);
+                        if (node instanceof AST_Var && def.orig[0] instanceof AST_SymbolCatch) {
                             var redef = def.redefined();
-                        if (redef && node instanceof AST_Var) var_defs_by_id.add(redef.id, defn);
+                            if (redef) var_defs_by_id.add(redef.id, defn);
-                        if ((!drop_vars || (node instanceof AST_Const ? redef : def.const_redefs))
+                        }
+                        if ((!drop_vars || (node instanceof AST_Const ? def.redefined() : def.const_redefs))
                             && !(def.id in in_use_ids)) {
                             in_use_ids[def.id] = true;
                             in_use.push(def);

test/compress/drop-unused.js

@@ -3085,3 +3085,30 @@ issue_4184: {
     }
     expect_stdout: "42"
 }
+
+issue_4235: {
+    options = {
+        inline: true,
+        reduce_vars: true,
+        unused: true,
+        varify: true,
+    }
+    input: {
+        (function() {
+            {
+                const f = 0;
+            }
+            (function f() {
+                var f = console.log(f);
+            })();
+        })();
+    }
+    expect: {
+        (function() {
+            f = console.log(f),
+            void 0;
+            var f;
+        })();
+    }
+    expect_stdout: "undefined"
+}

test/compress/ie8.js

@@ -2859,3 +2859,21 @@ issue_4186: {
     }
     expect_stdout: "NaN"
 }
+
+issue_4235: {
+    options = {
+        ie8: true,
+        unused: true,
+    }
+    input: {
+        try {} catch (e) {}
+        console.log(function e() {
+            var e = 0;
+        }());
+    }
+    expect: {
+        try {} catch (e) {}
+        console.log(function e() {}());
+    }
+    expect_stdout: "undefined"
+}