fix corner case in spreads (#4883)

fixes #4882

lib/compress.js

@@ -11649,13 +11649,23 @@ merge(Compressor.prototype, {
             found = true;
             var exp = prop.expression;
             if (compressor.option("spreads") && exp instanceof AST_Object && all(exp.properties, function(prop) {
-                return !(prop instanceof AST_ObjectGetter || prop instanceof AST_Spread);
+                if (prop instanceof AST_ObjectGetter) return false;
+                if (prop instanceof AST_Spread) return false;
+                if (prop.key !== "__proto__") return true;
+                if (prop instanceof AST_ObjectSetter) return true;
+                return !prop.value.has_side_effects(compressor);
             })) {
                 changed = true;
                 exp.properties.forEach(function(prop) {
-                    process(prop instanceof AST_ObjectSetter ? make_node(AST_ObjectKeyVal, prop, {
-                        key: prop.key,
-                        value: make_node(AST_Undefined, prop).optimize(compressor)
+                    var key = prop.key;
+                    var setter = prop instanceof AST_ObjectSetter;
+                    if (key === "__proto__") {
+                        if (!setter) return;
+                        key = make_node_from_constant(key, prop);
+                    }
+                    process(setter ? make_node(AST_ObjectKeyVal, prop, {
+                        key: key,
+                        value: make_node(AST_Undefined, prop).optimize(compressor),
                     }) : prop);
                 });
             } else {
@@ -11695,7 +11705,7 @@ merge(Compressor.prototype, {
             if (key instanceof AST_Node) {
                 found = true;
                 key = key.evaluate(compressor);
-                if (key === prop.key) {
+                if (key === prop.key || key === "__proto__") {
                     generated = true;
                 } else {
                     key = prop.key = "" + key;
@@ -11711,9 +11721,7 @@ merge(Compressor.prototype, {
             if (found && !generated && typeof key == "string" && RE_POSITIVE_INTEGER.test(key)) {
                 generated = true;
                 if (keys.has(key)) prop = keys.get(key)[0];
-                prop.key = make_node(AST_Number, prop, {
-                    value: +key
-                });
+                prop.key = make_node(AST_Number, prop, { value: +key });
             }
         }
     });

test/compress/spreads.js

@@ -1068,3 +1068,91 @@ issue_4849: {
     expect_stdout: "object"
     node_version: ">=8"
 }
+
+issue_4882_1: {
+    options = {
+        objects: true,
+        spreads: true,
+    }
+    input: {
+        var o = {
+            p: "PASS",
+            ... {
+                __proto__: {
+                    p: "FAIL 1",
+                    q: "FAIL 2",
+                },
+            },
+        };
+        console.log(o.p);
+        console.log(o.q);
+    }
+    expect: {
+        var o = {
+            p: "PASS",
+        };
+        console.log(o.p);
+        console.log(o.q);
+    }
+    expect_stdout: [
+        "PASS",
+        "undefined",
+    ]
+    node_version: ">=8"
+}
+
+issue_4882_2: {
+    options = {
+        objects: true,
+        spreads: true,
+    }
+    input: {
+        console.log(null == Object.getPrototypeOf({
+            ... {
+                __proto__: (console.log(42), null),
+            },
+        }) ? "FAIL" : "PASS");
+    }
+    expect: {
+        console.log(null == Object.getPrototypeOf({
+            ... {
+                __proto__: (console.log(42), null),
+            },
+        }) ? "FAIL" : "PASS");
+    }
+    expect_stdout: [
+        "42",
+        "PASS",
+    ]
+    node_version: ">=8"
+}
+
+issue_4882_3: {
+    options = {
+        objects: true,
+        spreads: true,
+    }
+    input: {
+        var o = {
+            __proto__: { p: 42 },
+            ... {
+                set __proto__(v) {},
+            },
+        };
+        console.log(o.__proto__ === Object.getPrototypeOf(o) ? "FAIL" : "PASS");
+        console.log(o.p);
+    }
+    expect: {
+        var o = {
+            __proto__: { p: 42 },
+            ["__proto__"]: void 0,
+        };
+        console.log(o.__proto__ === Object.getPrototypeOf(o) ? "FAIL" : "PASS");
+        console.log(o.p);
+    }
+    expect_stdout: [
+        "PASS",
+        "42",
+    ]
+    node_version: ">=8"
+}