enhance join_vars (#5824)

closes #5790

Author: alexlamsl

lib/compress.js

@@ -4222,16 +4222,48 @@ Compressor.prototype.compress = function(node) {
                 if (value.left instanceof AST_SymbolRef) names.set(value.left.name, true);
                 value = value.right;
             }
-            if (!(value instanceof AST_Object)) return;
-            var trimmed = false;
-            do {
-                if (!try_join(exprs[0])) break;
-                exprs.shift();
-                trimmed = true;
-            } while (exprs.length);
-            return trimmed;
+            if (value instanceof AST_Array) {
+                var trimmed = false;
+                do {
+                    if (!try_join_array(exprs[0])) break;
+                    exprs.shift();
+                    trimmed = true;
+                } while (exprs.length);
+                return trimmed;
+            } else if (value instanceof AST_Object) {
+                var trimmed = false;
+                do {
+                    if (!try_join_object(exprs[0])) break;
+                    exprs.shift();
+                    trimmed = true;
+                } while (exprs.length);
+                return trimmed;
+            }
+
+            function try_join_array(node) {
+                if (!(node instanceof AST_Assign)) return;
+                if (node.operator != "=") return;
+                if (!(node.left instanceof AST_PropAccess)) return;
+                var sym = node.left.expression;
+                if (!(sym instanceof AST_SymbolRef)) return;
+                if (!names.has(sym.name)) return;
+                if (!node.right.is_constant_expression(scope)) return;
+                var prop = node.left.property;
+                if (prop instanceof AST_Node) {
+                    if (try_join_array(prop)) prop = node.left.property = prop.right.clone();
+                    prop = prop.evaluate(compressor);
+                }
+                if (prop instanceof AST_Node) return;
+                if (!RE_POSITIVE_INTEGER.test("" + prop)) return;
+                prop = +prop;
+                var len = value.elements.length;
+                if (prop > len + 4) return;
+                while (len < prop) value.elements[len++] = make_node(AST_Hole, value);
+                value.elements[prop] = node.right;
+                return true;
+            }
 
-            function try_join(node) {
+            function try_join_object(node) {
                 if (!(node instanceof AST_Assign)) return;
                 if (node.operator != "=") return;
                 if (!(node.left instanceof AST_PropAccess)) return;
@@ -4241,7 +4273,7 @@ Compressor.prototype.compress = function(node) {
                 if (!node.right.is_constant_expression(scope)) return;
                 var prop = node.left.property;
                 if (prop instanceof AST_Node) {
-                    if (try_join(prop)) prop = node.left.property = prop.right.clone();
+                    if (try_join_object(prop)) prop = node.left.property = prop.right.clone();
                     prop = prop.evaluate(compressor);
                 }
                 if (prop instanceof AST_Node) return;

test/compress/join_vars.js

@@ -16,6 +16,104 @@ join_vars_assign: {
     expect_stdout: "PASS"
 }
 
+join_array_assignments_1: {
+    options = {
+        evaluate: true,
+        join_vars: true,
+    }
+    input: {
+        console.log(function () {
+            var a = ["foo", , "bar"];
+            a[1] = "baz";
+            a[7] = "moo";
+            a[0] = "moz";
+            return a;
+        }().join());
+    }
+    expect: {
+        console.log(function () {
+            var a = ["moz", "baz", "bar", , , , , "moo"];
+            return a;
+        }().join());
+    }
+    expect_stdout: "moz,baz,bar,,,,,moo"
+}
+
+join_array_assignments_2: {
+    options = {
+        evaluate: true,
+        join_vars: true,
+    }
+    input: {
+        console.log(function () {
+            var a = ["foo"];
+            a[1] = "bar";
+            a[7] = "baz";
+            a[2] = "moo";
+            return a;
+        }().join());
+    }
+    expect: {
+        console.log(function () {
+            var a = ["foo", "bar"];
+            a[7] = "baz";
+            a[2] = "moo";
+            return a;
+        }().join());
+    }
+    expect_stdout: "foo,bar,moo,,,,,baz"
+}
+
+join_array_assignments_3: {
+    options = {
+        evaluate: true,
+        join_vars: true,
+    }
+    input: {
+        console.log(function () {
+            var a = ["foo"];
+            a[1] = "bar";
+            a.b = "baz";
+            a[2] = "moo";
+            return a;
+        }().join());
+    }
+    expect: {
+        console.log(function () {
+            var a = ["foo", "bar"];
+            a.b = "baz";
+            a[2] = "moo";
+            return a;
+        }().join());
+    }
+    expect_stdout: true
+}
+
+join_array_assignments_4: {
+    options = {
+        evaluate: true,
+        join_vars: true,
+    }
+    input: {
+        console.log(function () {
+            var a = ["foo"];
+            a[0] = "bar";
+            a[1] = a;
+            a[2] = "baz";
+            return a;
+        }().join());
+    }
+    expect: {
+        console.log(function () {
+            var a = ["bar"];
+            a[1] = a;
+            a[2] = "baz";
+            return a;
+        }().join());
+    }
+    expect_stdout: true
+}
+
 join_object_assignments_1: {
     options = {
         evaluate: true,