Add comprehensive tests for typeof guard patterns in side effect analysis

Co-authored-by: sapphi-red <49056869+sapphi-red@users.noreply.github.com>

Author: Copilot

crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs

@@ -832,3 +832,68 @@ fn test_object_with_to_primitive_related_properties_overridden() {
     test("+{ ...{ valueOf() { return Symbol() } } }", true);
     test("+{ ...{ [Symbol.toPrimitive]() { return Symbol() } } }", true);
 }
+
+#[test]
+fn test_typeof_guard_patterns() {
+    // Test patterns with global variables that should be side-effect-free
+    // when properly guarded with typeof checks
+
+    // Logical AND patterns - typeof x !== 'undefined' && x
+    test_with_global_variables("typeof x !== 'undefined' && x", vec!["x".to_string()], false);
+    test_with_global_variables("typeof x != 'undefined' && x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' !== typeof x && x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' != typeof x && x", vec!["x".to_string()], false);
+
+    // Logical OR patterns - typeof x === 'undefined' || x
+    test_with_global_variables("typeof x === 'undefined' || x", vec!["x".to_string()], false);
+    test_with_global_variables("typeof x == 'undefined' || x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' === typeof x || x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' == typeof x || x", vec!["x".to_string()], false);
+
+    // String comparison patterns - typeof x < 'u' && x
+    test_with_global_variables("typeof x < 'u' && x", vec!["x".to_string()], false);
+    test_with_global_variables("typeof x <= 'u' && x", vec!["x".to_string()], false);
+    test_with_global_variables("'u' > typeof x && x", vec!["x".to_string()], false);
+    test_with_global_variables("'u' >= typeof x && x", vec!["x".to_string()], false);
+
+    // Conditional patterns - typeof x === 'undefined' ? fallback : x
+    test_with_global_variables("typeof x === 'undefined' ? 0 : x", vec!["x".to_string()], false);
+    test_with_global_variables("typeof x == 'undefined' ? 0 : x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' === typeof x ? 0 : x", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' == typeof x ? 0 : x", vec!["x".to_string()], false);
+
+    // Conditional patterns - typeof x !== 'undefined' ? x : fallback
+    test_with_global_variables("typeof x !== 'undefined' ? x : 0", vec!["x".to_string()], false);
+    test_with_global_variables("typeof x != 'undefined' ? x : 0", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' !== typeof x ? x : 0", vec!["x".to_string()], false);
+    test_with_global_variables("'undefined' != typeof x ? x : 0", vec!["x".to_string()], false);
+
+    // These should still have side effects because the fallback/other expressions have side effects
+    test_with_global_variables("typeof x !== 'undefined' && (x + foo())", vec!["x".to_string()], true);
+    test_with_global_variables("typeof x === 'undefined' || (x + foo())", vec!["x".to_string()], true);
+    test_with_global_variables("typeof x === 'undefined' ? foo() : x", vec!["x".to_string()], true);
+    test_with_global_variables("typeof x !== 'undefined' ? x : foo()", vec!["x".to_string()], true);
+
+    // These should still have side effects because the guard condition itself has side effects
+    test_with_global_variables("typeof foo() !== 'undefined' && x", vec!["x".to_string()], true);
+    test_with_global_variables("typeof foo() === 'undefined' || x", vec!["x".to_string()], true);
+    test_with_global_variables("typeof foo() === 'undefined' ? 0 : x", vec!["x".to_string()], true);
+
+    // These should still have side effects because the variable name doesn't match
+    test_with_global_variables("typeof y !== 'undefined' && x", vec!["x".to_string(), "y".to_string()], true);
+    test_with_global_variables("typeof y === 'undefined' || x", vec!["x".to_string(), "y".to_string()], true);
+    test_with_global_variables("typeof y === 'undefined' ? 0 : x", vec!["x".to_string(), "y".to_string()], true);
+
+    // Test that accessing non-global variables is side-effect-free
+    test("localVar", false);
+    
+    // These should be side-effect-free when the variable is not declared as global
+    // because such variables are treated as having no side effects when accessed
+    test("typeof localVar !== 'undefined' && localVar", false);
+    test("typeof localVar === 'undefined' || localVar", false);
+    test("typeof localVar === 'undefined' ? 0 : localVar", false);
+
+    // Test multiple variables
+    test_with_global_variables("typeof x !== 'undefined' && typeof y !== 'undefined' && x && y", vec!["x".to_string(), "y".to_string()], true); // Still has side effects because both x and y are accessed
+    test_with_global_variables("typeof x !== 'undefined' && x", vec!["x".to_string(), "y".to_string()], false);
+}