enhance merge_vars (#5349)

lib/compress.js

@@ -6025,10 +6025,7 @@ Compressor.prototype.compress = function(node) {
             }
             if (node instanceof AST_Binary) {
                 if (!lazy_op[node.operator]) return;
-                node.left.walk(tw);
+                walk_cond(node);
-                push();
-                node.right.walk(tw);
-                pop();
                 return true;
             }
             if (node instanceof AST_Break) {
@@ -6053,13 +6050,7 @@ Compressor.prototype.compress = function(node) {
                 return true;
             }
             if (node instanceof AST_Conditional) {
-                node.condition.walk(tw);
+                walk_cond(node.condition, node.consequent, node.alternative);
-                push();
-                node.consequent.walk(tw);
-                pop();
-                push();
-                node.alternative.walk(tw);
-                pop();
                 return true;
             }
             if (node instanceof AST_Continue) {
@@ -6100,15 +6091,7 @@ Compressor.prototype.compress = function(node) {
                 return true;
             }
             if (node instanceof AST_If) {
-                node.condition.walk(tw);
+                walk_cond(node.condition, node.body, node.alternative);
-                push();
-                node.body.walk(tw);
-                pop();
-                if (node.alternative) {
-                    push();
-                    node.alternative.walk(tw);
-                    pop();
-                }
                 return true;
             }
             if (node instanceof AST_LabeledStatement) {
@@ -6276,6 +6259,41 @@ Compressor.prototype.compress = function(node) {
                 }
                 return true;
             }
+
+            function walk_cond(condition, consequent, alternative) {
+                var save = segment;
+                var segments = [ save, save ];
+                if (condition instanceof AST_Binary) switch (condition.operator) {
+                  case "&&":
+                    segments[0] = walk_cond(condition.left, condition.right)[0];
+                    break;
+                  case "||":
+                  case "??":
+                    segments[1] = walk_cond(condition.left, null, condition.right)[1];
+                    break;
+                  default:
+                    condition.walk(tw);
+                    break;
+                } else if (condition instanceof AST_Conditional) {
+                    walk_cond(condition.condition, condition.consequent, condition.alternative);
+                } else {
+                    condition.walk(tw);
+                }
+                segment = segments[0];
+                if (consequent) {
+                    push();
+                    consequent.walk(tw);
+                }
+                segments[0] = segment;
+                segment = segments[1];
+                if (alternative) {
+                    push();
+                    alternative.walk(tw);
+                }
+                segments[1] = segment;
+                segment = save;
+                return segments;
+            }
         });
         tw.directives = Object.create(compressor.directives);
         self.walk(tw);

test/compress/merge_vars.js

@@ -169,6 +169,158 @@ conditional_branch: {
     expect_stdout: "PASS"
 }
 
+conditional_chain_1: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        function f(a, b) {
+            var c, d;
+            if (a && (c = a))
+                console.log(c);
+            else
+                b || (d = b) ? console.log("foo") : console.log(d);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect: {
+        function f(a, b) {
+            var a, a;
+            if (a && (a = a))
+                console.log(a);
+            else
+                b || (a = b) ? console.log("foo") : console.log(a);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect_stdout: [
+        "null",
+        "foo",
+        "42",
+        "42",
+    ]
+}
+
+conditional_chain_2: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        function f(a, b) {
+            var c, d;
+            if (a && (c = a))
+                console.log(c);
+            else
+                b || (d = b) ? console.log(c) : console.log(d);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect: {
+        function f(a, b) {
+            var c, a;
+            if (a && (c = a))
+                console.log(c);
+            else
+                b || (a = b) ? console.log(c) : console.log(a);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect_stdout: [
+        "null",
+        "undefined",
+        "42",
+        "42",
+    ]
+}
+
+conditional_chain_3: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        function f(a, b) {
+            var c, d;
+            if (a && (c = a) || b || (d = b))
+                console.log(c);
+            else
+                console.log(d);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect: {
+        function f(a, b) {
+            var c, a;
+            if (a && (c = a) || b || (a = b))
+                console.log(c);
+            else
+                console.log(a);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect_stdout: [
+        "null",
+        "undefined",
+        "42",
+        "42",
+    ]
+}
+
+conditional_chain_4: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        function f(a, b) {
+            var c, d;
+            if (a && b ? c = a : d = b)
+                console.log(c);
+            else
+                console.log(d);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect: {
+        function f(a, b) {
+            var c, d;
+            if (a && b ? c = a : d = b)
+                console.log(c);
+            else
+                console.log(d);
+        }
+        f("", null);
+        f("", true);
+        f(42, null);
+        f(42, true);
+    }
+    expect_stdout: [
+        "null",
+        "undefined",
+        "null",
+        "42",
+    ]
+}
+
 if_branch: {
     options = {
         merge_vars: true,