From 0ce71bbec0c9f0d49ec86f8b959f12a7bf9df21d Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Thu, 16 Apr 2020 22:31:33 +0100
Subject: [PATCH] enhance `join_vars` (#3783)

---
 lib/compress.js                | 37 +++++++++++++++++++++++++++++-----
 test/compress/collapse_vars.js |  7 ++++---
 test/compress/drop-unused.js   | 18 +++++++++++++++++
 test/compress/hoist_props.js   | 20 +++++++++---------
 test/compress/properties.js    |  4 ++--
 5 files changed, 65 insertions(+), 21 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index e5b7bf09..18cbd05e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2338,10 +2338,7 @@ merge(Compressor.prototype, {
                 exprs = body.expressions.slice();
             }
             if (!exprs) return;
-            if (defn instanceof AST_Definitions) {
-                var def = defn.definitions[defn.definitions.length - 1];
-                if (trim_assigns(def.name, def.value, exprs)) return exprs;
-            }
+            var trimmed = false;
             for (var i = exprs.length - 1; --i >= 0;) {
                 var expr = exprs[i];
                 if (!(expr instanceof AST_Assign)) continue;
@@ -2349,8 +2346,38 @@ merge(Compressor.prototype, {
                 if (!(expr.left instanceof AST_SymbolRef)) continue;
                 var tail = exprs.slice(i + 1);
                 if (!trim_assigns(expr.left, expr.right, tail)) continue;
-                return exprs.slice(0, i + 1).concat(tail);
+                trimmed = true;
+                exprs = exprs.slice(0, i + 1).concat(tail);
             }
+            if (defn instanceof AST_Definitions) {
+                var def = defn.definitions[defn.definitions.length - 1];
+                if (trim_assigns(def.name, def.value, exprs)) trimmed = true;
+                if (join_var_assign(defn.definitions, exprs)) trimmed = true;
+            }
+            return trimmed && exprs;
+        }
+
+        function join_var_assign(definitions, exprs) {
+            var trimmed = false;
+            while (exprs.length) {
+                var expr = exprs[0];
+                if (!(expr instanceof AST_Assign)) break;
+                if (expr.operator != "=") break;
+                var lhs = expr.left;
+                if (!(lhs instanceof AST_SymbolRef)) break;
+                var def = lhs.definition();
+                if (def.scope !== scope) break;
+                var name = make_node(AST_SymbolVar, lhs, lhs);
+                definitions.push(make_node(AST_VarDef, expr, {
+                    name: name,
+                    value: expr.right
+                }));
+                def.orig.push(name);
+                def.replaced++;
+                exprs.shift();
+                trimmed = true;
+            }
+            return trimmed;
         }
 
         function trim_assigns(name, value, exprs) {
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 99e57b32..a9167262 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -804,7 +804,7 @@ collapse_vars_assignment: {
         function log(x) { return console.log(x), x; }
         function f0(c) {
             var a = 3 / c;
-            return a = a;
+            return a;
         }
         function f1(c) {
             return 1 - 3 / c;
@@ -2012,6 +2012,7 @@ issue_1631_3: {
         join_vars: true,
         sequences: true,
         side_effects: true,
+        unused: true,
     }
     input: {
         function g() {
@@ -2031,8 +2032,8 @@ issue_1631_3: {
             function f() {
                 return a = 2, 4;
             }
-            var a = 0, b = 1, t = f();
-            return b = a + t;
+            var a = 0, t = f();
+            return a + t;
         }
         console.log(g());
     }
diff --git a/test/compress/drop-unused.js b/test/compress/drop-unused.js
index 99ab7b40..949106c2 100644
--- a/test/compress/drop-unused.js
+++ b/test/compress/drop-unused.js
@@ -2444,3 +2444,21 @@ issue_3746: {
     }
     expect_stdout: "PASS"
 }
+
+join_vars_assign: {
+    options = {
+        join_vars: true,
+        unused: true,
+    }
+    input: {
+        var y, x;
+        x = Object("PAS");
+        y = Object("S");
+        console.log(x + y);
+    }
+    expect: {
+        var x = Object("PAS"), y = Object("S");
+        console.log(x + y);
+    }
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/hoist_props.js b/test/compress/hoist_props.js
index c647ccc1..563c7aab 100644
--- a/test/compress/hoist_props.js
+++ b/test/compress/hoist_props.js
@@ -767,18 +767,17 @@ issue_3071_1: {
             var obj = {};
             obj.one = 1;
             obj.two = 2;
-            console.log(obj.one);
+            console.log(obj.one, obj.two);
         })();
     }
     expect: {
-        console.log(1);
+        console.log(1, 2);
     }
-    expect_stdout: "1"
+    expect_stdout: "1 2"
 }
 
 issue_3071_2: {
     options = {
-        evaluate: true,
         hoist_props: true,
         inline: true,
         join_vars: true,
@@ -793,19 +792,18 @@ issue_3071_2: {
             obj = {};
             obj.one = 1;
             obj.two = 2;
-            console.log(obj.one);
+            console.log(obj.one, obj.two);
             var obj;
         })();
     }
     expect: {
-        console.log(1);
+        console.log(1, 2);
     }
-    expect_stdout: "1"
+    expect_stdout: "1 2"
 }
 
 issue_3071_2_toplevel: {
     options = {
-        evaluate: true,
         hoist_props: true,
         inline: true,
         join_vars: true,
@@ -821,14 +819,14 @@ issue_3071_2_toplevel: {
             obj = {};
             obj.one = 1;
             obj.two = 2;
-            console.log(obj.one);
+            console.log(obj.one, obj.two);
             var obj;
         })();
     }
     expect: {
-        console.log(1);
+        console.log(1, 2);
     }
-    expect_stdout: "1"
+    expect_stdout: "1 2"
 }
 
 issue_3071_3: {
diff --git a/test/compress/properties.js b/test/compress/properties.js
index 9270f438..b23c362c 100644
--- a/test/compress/properties.js
+++ b/test/compress/properties.js
@@ -1875,8 +1875,8 @@ join_expr: {
     expect: {
         var c = "FAIL";
         (function() {
-            var a = 0;
-            switch (a = { b: 0 }, a.b) {
+            var a = 0, a = { b: 0 };
+            switch (a.b) {
               case 0:
                 c = "PASS";
             }
-- 
2.34.1