fix corner cases in booleans & conditionals (#5695)

fixes #5694

lib/compress.js

@@ -1748,6 +1748,7 @@ Compressor.prototype.compress = function(node) {
 
     var identifier_atom = makePredicate("Infinity NaN undefined");
     function is_lhs_read_only(lhs, compressor) {
+        if (lhs instanceof AST_Atom) return true;
         if (lhs instanceof AST_ObjectIdentity) return true;
         if (lhs instanceof AST_PropAccess) {
             if (lhs.property === "__proto__") return true;
@@ -11589,10 +11590,12 @@ Compressor.prototype.compress = function(node) {
         if (node instanceof AST_Unary) return true;
     }
 
-    function extract_lhs(node) {
-        if (node instanceof AST_Assign) return node.left;
+    function extract_lhs(node, compressor) {
+        if (node instanceof AST_Assign) return is_lhs_read_only(node.left, compressor) ? node : node.left;
         if (node instanceof AST_Sequence) return extract_lhs(node.tail_node());
-        if (node instanceof AST_UnaryPrefix && UNARY_POSTFIX[node.operator]) return node.expression;
+        if (node instanceof AST_UnaryPrefix && UNARY_POSTFIX[node.operator]) {
+            return is_lhs_read_only(node.expression, compressor) ? node : node.expression;
+        }
         return node;
     }
 
@@ -11601,6 +11604,7 @@ Compressor.prototype.compress = function(node) {
         if (node instanceof AST_Sub) {
             return repeatable(compressor, node.expression) && repeatable(compressor, node.property);
         }
+        if (node instanceof AST_Symbol) return true;
         return !node.has_side_effects(compressor);
     }
 
@@ -11637,7 +11641,7 @@ Compressor.prototype.compress = function(node) {
             if (seq !== self) return seq.optimize(compressor);
         }
         if (compressor.option("assignments") && lazy_op[self.operator]) {
-            var lhs = extract_lhs(self.left);
+            var lhs = extract_lhs(self.left, compressor);
             var right = self.right;
             // a || (a = x) ---> a = a || x
             // (a = x) && (a = y) ---> a = (a = x) && y
@@ -11737,7 +11741,7 @@ Compressor.prototype.compress = function(node) {
         var in_bool = false;
         var parent = compressor.parent();
         if (compressor.option("booleans")) {
-            var lhs = extract_lhs(self.left);
+            var lhs = extract_lhs(self.left, compressor);
             if (lazy_op[self.operator] && !lhs.has_side_effects(compressor)) {
                 // a || a ---> a
                 // (a = x) && a --> a = x
@@ -12898,7 +12902,7 @@ Compressor.prototype.compress = function(node) {
         }
         var consequent = self.consequent;
         var alternative = self.alternative;
-        var cond_lhs = extract_lhs(condition);
+        var cond_lhs = extract_lhs(condition, compressor);
         if (repeatable(compressor, cond_lhs)) {
             // x ? x : y ---> x || y
             if (cond_lhs.equals(consequent)) return make_node(AST_Binary, self, {

test/compress/booleans.js

@@ -830,3 +830,20 @@ issue_5469: {
     }
     expect_stdout: "undefined"
 }
+
+issue_5694: {
+    options = {
+        booleans: true,
+        conditionals: true,
+    }
+    input: {
+        var undefined;
+        // Node.js v0.12~6 (vm): 42
+        console.log((undefined = 42) && undefined);
+    }
+    expect: {
+        var undefined;
+        console.log((undefined = 42) && undefined);
+    }
+    expect_stdout: true
+}

test/compress/comparisons.js

@@ -76,14 +76,12 @@ self_comparison_1: {
         comparisons: true,
     }
     input: {
-        var a, b;
         a === a;
         a !== b;
         b.c === a.c;
         b.c !== b.c;
     }
     expect: {
-        var a, b;
         a == a;
         a !== b;
         b.c === a.c;

test/compress/conditionals.js

@@ -3033,3 +3033,21 @@ issue_5673_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5694: {
+    options = {
+        conditionals: true,
+    }
+    input: {
+        FORCE_EXEC = "async()=>{}";
+        var a = "foo";
+        // Node.js v0.12~6 (vm): foo
+        console.log((NaN = a) ? NaN : 42);
+    }
+    expect: {
+        FORCE_EXEC = "async()=>{}";
+        var a = "foo";
+        console.log((NaN = a) ? NaN : 42);
+    }
+    expect_stdout: "NaN"
+}

test/compress/if_return.js

@@ -976,33 +976,33 @@ nested_if_return: {
         if_return: true,
     }
     input: {
-        function f(a, b, c, d, e, f, g, h, i, j, k, l, m, n) {
-            if (a) {
-                if (b)
-                    return b;
-                if (c)
-                    return d;
-                if (e)
-                    return f;
-                if (g)
-                    return h;
-                if (i) {
-                    if (j)
-                        return k;
+        function f() {
+            if (A) {
+                if (B)
+                    return B;
+                if (C)
+                    return D;
+                if (E)
+                    return F;
+                if (G)
+                    return H;
+                if (I) {
+                    if (J)
+                        return K;
                     return;
                 }
-                if (l) {
-                    if (m)
+                if (L) {
+                    if (M)
                         return;
-                    return n;
+                    return N;
                 }
             }
         }
     }
     expect: {
-        function f(a, b, c, d, e, f, g, h, i, j, k, l, m, n) {
-            if (a)
-                return b || (c ? d : e ? f : g ? h : i ? j ? k : void 0 : l && !m ? n : void 0);
+        function f() {
+            if (A)
+                return B || (C ? D : E ? F : G ? H : I ? J ? K : void 0 : L && !M ? N : void 0);
         }
     }
 }