fix corner cases in booleans (#5029)

fixes #5028

lib/compress.js

@@ -8283,7 +8283,9 @@ merge(Compressor.prototype, {
         if (is_empty(self.alternative)) self.alternative = null;
 
         if (!compressor.option("conditionals")) return self;
-        if (compressor.option("booleans")) mark_duplicate_condition(compressor, self.condition);
+        if (compressor.option("booleans") && !self.condition.has_side_effects(compressor)) {
+            mark_duplicate_condition(compressor, self.condition);
+        }
         // if condition can be statically determined, warn and drop
         // one of the blocks.  note, statically determined implies
         // “has no side effects”; also it doesn't work for cases like
@@ -11335,8 +11337,11 @@ merge(Compressor.prototype, {
             return make_sequence(self, expressions);
         }
         if (!compressor.option("conditionals")) return self;
-        if (compressor.option("booleans")) mark_duplicate_condition(compressor, self.condition);
-        var condition = fuzzy_eval(compressor, self.condition);
+        var condition = self.condition;
+        if (compressor.option("booleans") && !condition.has_side_effects(compressor)) {
+            mark_duplicate_condition(compressor, condition);
+        }
+        condition = fuzzy_eval(compressor, condition);
         if (!condition) {
             AST_Node.warn("Condition always false [{file}:{line},{col}]", self.start);
             return make_sequence(self, [ self.condition, self.alternative ]).optimize(compressor);

test/compress/booleans.js

@@ -558,3 +558,79 @@ issue_4374: {
     }
     expect_stdout: "0"
 }
+
+issue_5028_1: {
+    options = {
+        booleans: true,
+        conditionals: true,
+    }
+    input: {
+        var a = 1;
+        console.log(function() {
+            return a-- ? a-- ? "FAIL 1" : "PASS" : "FAIL 2";
+        }());
+    }
+    expect: {
+        var a = 1;
+        console.log(function() {
+            return a-- ? a-- ? "FAIL 1" : "PASS" : "FAIL 2";
+        }());
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5028_2: {
+    options = {
+        booleans: true,
+        conditionals: true,
+        dead_code: true,
+        if_return: true,
+    }
+    input: {
+        var a = 1;
+        (function() {
+            if (a--)
+                if (a--)
+                    a = "FAIL";
+                else
+                    return;
+        })();
+        console.log(a);
+    }
+    expect: {
+        var a = 1;
+        (function() {
+            a-- && a-- && (a = "FAIL");
+        })();
+        console.log(a);
+    }
+    expect_stdout: "-1"
+}
+
+issue_5028_3: {
+    options = {
+        booleans: true,
+        conditionals: true,
+        evaluate: true,
+        if_return: true,
+    }
+    input: {
+        var a = 1;
+        (function() {
+            if (a--)
+                if (a--)
+                    a = "FAIL";
+                else
+                    return;
+        })();
+        console.log(a);
+    }
+    expect: {
+        var a = 1;
+        (function() {
+            a-- && a-- && (a = "FAIL");
+        })();
+        console.log(a);
+    }
+    expect_stdout: "-1"
+}