fix corner case in collapse_vars (#5482)

fixes #5481

lib/compress.js

@@ -2466,6 +2466,13 @@ Compressor.prototype.compress = function(node) {
                     abort = false;
                     return true;
                 }
+                if (node instanceof AST_Class) {
+                    if (!in_try) return false;
+                    var base = node.extends;
+                    if (!base) return false;
+                    if (base instanceof AST_SymbolRef) base = base.fixed_value();
+                    return !safe_for_extends(base);
+                }
                 if (node instanceof AST_Exit) {
                     if (in_try) {
                         if (in_try.bfinally) return true;

test/compress/classes.js

@@ -2852,3 +2852,33 @@ issue_5436: {
     expect_stdout: "PASS"
     node_version: ">=12"
 }
+
+issue_5481: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        "use strict";
+        var a = "FAIL 1", log = console.log;
+        try {
+            a = "PASS";
+            (class extends 42 {});
+            log("FAIL 2", a);
+        } catch (e) {
+            log(a);
+        }
+    }
+    expect: {
+        "use strict";
+        var a = "FAIL 1", log = console.log;
+        try {
+            a = "PASS";
+            (class extends 42 {});
+            log("FAIL 2", a);
+        } catch (e) {
+            log(a);
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}

test/ufuzz/index.js

@@ -2398,7 +2398,7 @@ function patch_try_catch(orig, toplevel) {
                     "throw " + match[1] + ";",
                 ].join("\n");
             }
-            var new_code = code.slice(0, index) + insert + code.slice(index) + tail_throw;
+            var new_code = code.slice(0, index) + insert + code.slice(index) + tail_throw + "var UFUZZ_ERROR;";
             var result = run_code(new_code, toplevel);
             if (!sandbox.is_error(result)) {
                 if (!stack.filled && match[1]) stack.push({