From ba71bcc245c7594c42530074f953be3797f54b85 Mon Sep 17 00:00:00 2001
From: alexlamsl <alexlamsl@gmail.com>
Date: Sun, 12 Dec 2021 22:45:15 +0800
Subject: [PATCH] improve `merge_vars` usability

closes #5144
closes #5211
---
 lib/compress.js                  |   6 +-
 test/compress/awaits.js          |  14 +-
 test/compress/destructured.js    |  10 +-
 test/compress/hoist_props.js     |   8 +-
 test/compress/ie.js              |   8 +-
 test/compress/merge_vars.js      | 332 +++++++++++++++----------------
 test/compress/optional-chains.js |   8 +-
 test/compress/rests.js           |  18 +-
 test/compress/varify.js          |  16 +-
 test/compress/yields.js          |  14 +-
 10 files changed, 219 insertions(+), 215 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index b5c67c2d..4ff0b1d0 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6059,13 +6059,17 @@ Compressor.prototype.compress = function(node) {
                 var orig = [], refs = [];
                 tail_refs.forEach(function(sym) {
                     sym.thedef = def;
-                    sym.name = def.name;
                     if (sym instanceof AST_SymbolRef) {
                         refs.push(sym);
                     } else {
                         orig.push(sym);
                     }
                 });
+                var name = tail.definition.name;
+                def.forEach(function(sym) {
+                    sym.name = name;
+                });
+                def.name = name;
                 def.orig = orig.concat(def.orig);
                 def.references = refs.concat(def.references);
                 def.fixed = tail.definition.fixed && def.fixed;
diff --git a/test/compress/awaits.js b/test/compress/awaits.js
index 34479d48..36af41fd 100644
--- a/test/compress/awaits.js
+++ b/test/compress/awaits.js
@@ -1262,10 +1262,10 @@ issue_4454_2: {
         f("PASS");
     }
     expect: {
-        function f(b) {
-            (async function(c = console.log(b)) {})();
-            var b = 42..toString();
-            console.log(b);
+        function f(a) {
+            (async function(c = console.log(a)) {})();
+            var a = 42..toString();
+            console.log(a);
         }
         f("PASS");
     }
@@ -1965,10 +1965,10 @@ issue_5032_normal: {
             console.log(value);
             return value;
         }
-        async function f(c) {
-            var b = log(c), c = b;
+        async function f(a) {
+            var b = log(a), a = b;
             log(b);
-            log(c);
+            log(a);
         }
         f("PASS");
     }
diff --git a/test/compress/destructured.js b/test/compress/destructured.js
index 5acc7f69..81386e37 100644
--- a/test/compress/destructured.js
+++ b/test/compress/destructured.js
@@ -1844,13 +1844,13 @@ issue_4294: {
     expect: {
         A = "PASS";
         (function() {
-            var b = function({
-                [b]: {},
+            var a = function({
+                [a]: {},
             }) {}({
-                [b]: 0,
+                [a]: 0,
             });
-            var b = A;
-            console.log(b);
+            var a = A;
+            console.log(a);
         })();
     }
     expect_stdout: "PASS"
diff --git a/test/compress/hoist_props.js b/test/compress/hoist_props.js
index ab9a16f3..31c8439a 100644
--- a/test/compress/hoist_props.js
+++ b/test/compress/hoist_props.js
@@ -1163,13 +1163,13 @@ issue_5182: {
         log(o.p(42));
     }
     expect: {
-        var o_p = console;
-        log = o_p.log;
-        o_p = function(a) {
+        var o = console;
+        log = o.log;
+        o = function(a) {
             console.log(a ? "PASS" : "FAIL");
             return a;
         };
-        log(o_p(42));
+        log(o(42));
     }
     expect_stdout: [
         "PASS",
diff --git a/test/compress/ie.js b/test/compress/ie.js
index c275c88b..c4a78aeb 100644
--- a/test/compress/ie.js
+++ b/test/compress/ie.js
@@ -3109,9 +3109,9 @@ issue_5081_call: {
         }));
     }
     expect: {
-        function f(b) {
+        function f(a) {
             // IE5-10: TypeError: Function expected
-            return b(b = "A") + (b += "SS");
+            return a(a = "A") + (a += "SS");
         }
         console.log(f(function() {
             return "P";
@@ -3161,8 +3161,8 @@ issue_5081_property_access: {
         console.log(f({ A: "P" }));
     }
     expect: {
-        function f(b) {
-            return b[b = "A"] + (b += "SS");
+        function f(a) {
+            return a[a = "A"] + (a += "SS");
         }
         // IE9-11: undefinedASS
         console.log(f({ A: "P" }));
diff --git a/test/compress/merge_vars.js b/test/compress/merge_vars.js
index 9f89efe5..2fdb185d 100644
--- a/test/compress/merge_vars.js
+++ b/test/compress/merge_vars.js
@@ -19,11 +19,11 @@ merge: {
     expect: {
         var a = "foo";
         console.log(a);
-        function f(c) {
-            var c;
-            console.log(c);
-            c = "bar";
-            console.log(c);
+        function f(b) {
+            var b;
+            console.log(b);
+            b = "bar";
+            console.log(b);
         }
         f("baz");
         var d = "moo";
@@ -56,17 +56,17 @@ merge_toplevel: {
         console.log(d);
     }
     expect: {
-        var d = "foo";
-        console.log(d);
-        function f(c) {
-            var c;
-            console.log(c);
-            c = "bar";
-            console.log(c);
+        var a = "foo";
+        console.log(a);
+        function f(b) {
+            var b;
+            console.log(b);
+            b = "bar";
+            console.log(b);
         }
         f("baz");
-        var d = "moo";
-        console.log(d);
+        var a = "moo";
+        console.log(a);
     }
     expect_stdout: [
         "foo",
@@ -94,16 +94,16 @@ segment: {
         console.log(d);
     }
     expect: {
-        var d = "foo";
-        console.log(d);
-        for (var c, i = 0; i < 1; i++) {
-            var c = "bar";
-            console.log(c);
-            c = "baz";
-            console.log(c);
+        var a = "foo";
+        console.log(a);
+        for (var b, i = 0; i < 1; i++) {
+            var b = "bar";
+            console.log(b);
+            b = "baz";
+            console.log(b);
         }
-        var d = "moo";
-        console.log(d);
+        var a = "moo";
+        console.log(a);
     }
     expect_stdout: [
         "foo",
@@ -344,9 +344,9 @@ issue_4107: {
     }
     expect: {
         (function() {
-            (function(a) {
-                a = console || a;
-                console.log(typeof a);
+            (function(c) {
+                c = console || c;
+                console.log(typeof c);
             })();
         })();
         console.log(typeof a);
@@ -538,12 +538,12 @@ cross_branch_1_1: {
     expect: {
         var a;
         function f() {
-            var y, y;
+            var x, x;
             if (a)
-                y = "foo";
-            console.log(y);
-            y = "bar";
-            console.log(y);
+                x = "foo";
+            console.log(x);
+            x = "bar";
+            console.log(x);
         }
         a = 0;
         f();
@@ -581,13 +581,13 @@ cross_branch_1_2: {
     expect: {
         var a;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
-                console.log(y);
+                x = "foo";
+                console.log(x);
             }
-            y = "bar";
-            console.log(y);
+            x = "bar";
+            console.log(x);
         }
         a = 0;
         f();
@@ -624,13 +624,13 @@ cross_branch_1_3: {
     expect: {
         var a;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
-                console.log(y);
-                y = "bar";
+                x = "foo";
+                console.log(x);
+                x = "bar";
             }
-            console.log(y);
+            console.log(x);
         }
         a = 0;
         f();
@@ -666,12 +666,12 @@ cross_branch_1_4: {
     expect: {
         var a;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a)
-                console.log(y);
-            y = "bar";
-            console.log(y);
+                console.log(x);
+            x = "bar";
+            console.log(x);
         }
         a = 0;
         f();
@@ -751,12 +751,12 @@ cross_branch_1_6: {
     expect: {
         var a;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a) {
-                console.log(y);
-                y = "bar";
-                console.log(y);
+                console.log(x);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0;
@@ -835,12 +835,12 @@ cross_branch_1_8: {
     expect: {
         var a;
         function f() {
-            var y, y;
-            y = "foo";
-            console.log(y);
+            var x, x;
+            x = "foo";
+            console.log(x);
             if (a) {
-                y = "bar";
-                console.log(y);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0;
@@ -877,12 +877,12 @@ cross_branch_1_9: {
     expect: {
         var a;
         function f() {
-            var y, y;
-            y = "foo";
-            console.log(y);
-            y = "bar";
+            var x, x;
+            x = "foo";
+            console.log(x);
+            x = "bar";
             if (a)
-                console.log(y);
+                console.log(x);
         }
         a = 0;
         f();
@@ -924,14 +924,14 @@ cross_branch_2a_1: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
                 if (b)
-                    y = "foo";
-                console.log(y);
+                    x = "foo";
+                console.log(x);
             }
-            y = "bar";
-            console.log(y);
+            x = "bar";
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -980,14 +980,14 @@ cross_branch_2a_2: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
+                x = "foo";
                 if (b)
-                    console.log(y);
+                    console.log(x);
             }
-            y = "bar";
-            console.log(y);
+            x = "bar";
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -1035,14 +1035,14 @@ cross_branch_2a_3: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
                 if (b)
-                    y = "foo";
-                console.log(y);
-                y = "bar";
+                    x = "foo";
+                console.log(x);
+                x = "bar";
             }
-            console.log(y);
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -1092,15 +1092,15 @@ cross_branch_2a_4: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
                 if (b) {
-                    y = "foo";
-                    console.log(y);
+                    x = "foo";
+                    console.log(x);
                 }
-                y = "bar";
+                x = "bar";
             }
-            console.log(y);
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -1148,14 +1148,14 @@ cross_branch_2a_5: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
+                x = "foo";
                 if (b)
-                    console.log(y);
-                y = "bar";
+                    console.log(x);
+                x = "bar";
             }
-            console.log(y);
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -1427,13 +1427,13 @@ cross_branch_2a_10: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a) {
                 if (b)
-                    console.log(y);
-                y = "bar";
-                console.log(y);
+                    console.log(x);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0, b = 0;
@@ -1590,13 +1590,13 @@ cross_branch_2a_13: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a) {
-                console.log(y);
+                console.log(x);
                 if (b) {
-                    y = "bar";
-                    console.log(y);
+                    x = "bar";
+                    console.log(x);
                 }
             }
         }
@@ -1644,13 +1644,13 @@ cross_branch_2a_14: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a) {
-                console.log(y);
-                y = "bar";
+                console.log(x);
+                x = "bar";
                 if (b)
-                    console.log(y);
+                    console.log(x);
             }
         }
         a = 0, b = 0;
@@ -1753,13 +1753,13 @@ cross_branch_2a_16: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
-            console.log(y);
+            var x, x;
+            x = "foo";
+            console.log(x);
             if (a) {
-                y = "bar";
+                x = "bar";
                 if (b)
-                    console.log(y);
+                    console.log(x);
             }
         }
         a = 0, b = 0;
@@ -1807,13 +1807,13 @@ cross_branch_2b_1: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a)
-                y = "foo";
+                x = "foo";
             if (b)
-                console.log(y);
-            y = "bar";
-            console.log(y);
+                console.log(x);
+            x = "bar";
+            console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -1918,13 +1918,13 @@ cross_branch_2b_3: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a)
-                y = "foo";
+                x = "foo";
             if (b) {
-                console.log(y);
-                y = "bar";
-                console.log(y);
+                console.log(x);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0, b = 0;
@@ -2028,13 +2028,13 @@ cross_branch_2b_5: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a)
-                y = "foo";
-            console.log(y);
+                x = "foo";
+            console.log(x);
             if (b) {
-                y = "bar";
-                console.log(y);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0, b = 0;
@@ -2141,14 +2141,14 @@ cross_branch_2b_7: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
-                console.log(y);
+                x = "foo";
+                console.log(x);
             }
             if (b) {
-                y = "bar";
-                console.log(y);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0, b = 0;
@@ -2195,13 +2195,13 @@ cross_branch_2b_8: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a)
-                y = "foo";
-            console.log(y);
-            y = "bar";
+                x = "foo";
+            console.log(x);
+            x = "bar";
             if (b)
-                console.log(y);
+                console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -2250,14 +2250,14 @@ cross_branch_2b_9: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
-                console.log(y);
+                x = "foo";
+                console.log(x);
             }
-            y = "bar";
+            x = "bar";
             if (b)
-                console.log(y);
+                console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -2304,14 +2304,14 @@ cross_branch_2b_10: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
+            var x, x;
             if (a) {
-                y = "foo";
-                console.log(y);
-                y = "bar";
+                x = "foo";
+                console.log(x);
+                x = "bar";
             }
             if (b)
-                console.log(y);
+                console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -2412,13 +2412,13 @@ cross_branch_2b_12: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a)
-                console.log(y);
+                console.log(x);
             if (b) {
-                y = "bar";
-                console.log(y);
+                x = "bar";
+                console.log(x);
             }
         }
         a = 0, b = 0;
@@ -2465,13 +2465,13 @@ cross_branch_2b_13: {
     expect: {
         var a, b;
         function f() {
-            var y, y;
-            y = "foo";
+            var x, x;
+            x = "foo";
             if (a)
-                console.log(y);
-            y = "bar";
+                console.log(x);
+            x = "bar";
             if (b)
-                console.log(y);
+                console.log(x);
         }
         a = 0, b = 0;
         f();
@@ -2620,11 +2620,11 @@ issue_4126_1: {
             try {
                 console.log("PASS");
             } catch (e) {
-                var c = a;
+                var b = a;
             } finally {
-                var c = c;
+                var b = b;
             }
-            console.log(c);
+            console.log(b);
         }
         f("FAIL");
     }
@@ -2816,11 +2816,11 @@ conditional_write: {
         console.log(b);
     }
     expect: {
-        var b = "FAIL", b;
+        var a = "FAIL", a;
         if (console)
-            b = "PASS";
-        b = [b, 42].join();
-        console.log(b);
+            a = "PASS";
+        a = [a, 42].join();
+        console.log(a);
     }
     expect_stdout: "PASS,42"
 }
@@ -2994,13 +2994,13 @@ issue_4168_use_strict: {
     expect: {
         "use strict";
         var o = {
-            f: function(d, e, f) {
-                var d = d.d;
-                var e = e.e;
-                var f = f.f;
+            f: function(a, b, c) {
+                var a = a.d;
+                var b = b.e;
+                var c = c.f;
                 this.g(arguments);
-                if (d)
-                    console.log(e, f);
+                if (a)
+                    console.log(b, c);
             },
             g: function(args) {
                 console.log(args[0], args[1], args[2]);
@@ -3228,10 +3228,10 @@ issue_4653: {
         f(a++ + (b = b), b |= console.log(a));
     }
     expect: {
-        var b = 1;
+        var a = 1;
         (function(c, d) {
             c || console.log(d);
-        })(+b + (b = void 0), b |= console.log(2));
+        })(+a + (a = void 0), a |= console.log(2));
     }
     expect_stdout: [
         "2",
diff --git a/test/compress/optional-chains.js b/test/compress/optional-chains.js
index 8d16fdac..2cea8648 100644
--- a/test/compress/optional-chains.js
+++ b/test/compress/optional-chains.js
@@ -455,11 +455,11 @@ issue_5091: {
         console.log(f("FAIL 1") || "PASS");
     }
     expect: {
-        function f(b) {
-            var b = b.p;
+        function f(a) {
+            var a = a.p;
             var c;
-            b?.[c = "FAIL 2"];
-            return b || c;
+            a?.[c = "FAIL 2"];
+            return a || c;
         }
         console.log(f("FAIL 1") || "PASS");
     }
diff --git a/test/compress/rests.js b/test/compress/rests.js
index f377f637..8f032c67 100644
--- a/test/compress/rests.js
+++ b/test/compress/rests.js
@@ -436,9 +436,9 @@ merge_funarg: {
         })();
     }
     expect: {
-        (function(...b) {
-            var b = b.length;
-            console.log(b);
+        (function(...a) {
+            var a = a.length;
+            console.log(a);
         })();
     }
     expect_stdout: "0"
@@ -456,9 +456,9 @@ merge_funarg_destructured_array: {
         })([]);
     }
     expect: {
-        (function([ ...b ]) {
-            var b = b.length;
-            console.log(b);
+        (function([ ...a ]) {
+            var a = a.length;
+            console.log(a);
         })([]);
     }
     expect_stdout: "0"
@@ -476,9 +476,9 @@ merge_funarg_destructured_object: {
         })([ "PASS" ]);
     }
     expect: {
-        (function({ ...b }) {
-            var b = b[0];
-            console.log(b);
+        (function({ ...a }) {
+            var a = a[0];
+            console.log(a);
         })([ "PASS" ]);
     }
     expect_stdout: "PASS"
diff --git a/test/compress/varify.js b/test/compress/varify.js
index 4a90a955..0bc9ada2 100644
--- a/test/compress/varify.js
+++ b/test/compress/varify.js
@@ -13,10 +13,10 @@ reduce_merge_const: {
         console.log(b);
     }
     expect: {
-        var b = console;
-        console.log(typeof b);
-        b = typeof b;
-        console.log(b);
+        var a = console;
+        console.log(typeof a);
+        a = typeof a;
+        console.log(a);
     }
     expect_stdout: [
         "object",
@@ -41,10 +41,10 @@ reduce_merge_let: {
     }
     expect: {
         "use strict";
-        var b = console;
-        console.log(typeof b);
-        b = typeof b;
-        console.log(b);
+        var a = console;
+        console.log(typeof a);
+        a = typeof a;
+        console.log(a);
     }
     expect_stdout: [
         "object",
diff --git a/test/compress/yields.js b/test/compress/yields.js
index f0ffded3..7e28905e 100644
--- a/test/compress/yields.js
+++ b/test/compress/yields.js
@@ -864,10 +864,10 @@ issue_4454_2: {
         f("PASS");
     }
     expect: {
-        function f(b) {
-            (function*(c = console.log(b)) {})();
-            var b = 42..toString();
-            console.log(b);
+        function f(a) {
+            (function*(c = console.log(a)) {})();
+            var a = 42..toString();
+            console.log(a);
         }
         f("PASS");
     }
@@ -1177,10 +1177,10 @@ issue_5032_normal: {
             console.log(value);
             return value;
         }
-        function *f(c) {
-            var b = log(c), c = b;
+        function *f(a) {
+            var b = log(a), a = b;
             log(b);
-            log(c);
+            log(a);
         }
         f("PASS").next();
     }