fix corner case in collapse_vars (#3591)

lib/compress.js

@@ -1691,13 +1691,17 @@ merge(Compressor.prototype, {
                 if (expr instanceof AST_Unary) return false;
                 if (side_effects) return false;
                 if (value_def) return true;
-                if (lhs instanceof AST_SymbolRef) {
-                    var def = lhs.definition();
-                    if (def.references.length - def.replaced == (candidate instanceof AST_VarDef ? 1 : 2)) {
-                        return true;
-                    }
+                if (!(lhs instanceof AST_SymbolRef)) return false;
+                var referenced;
+                if (expr instanceof AST_VarDef) {
+                    referenced = 1;
+                } else if (expr.operator == "=") {
+                    referenced = 2;
+                } else {
+                    return false;
                 }
-                return false;
+                var def = lhs.definition();
+                return def.references.length - def.replaced == referenced;
             }
 
             function symbol_in_lvalues(sym, parent) {

test/compress/collapse_vars.js

@@ -6238,7 +6238,7 @@ issue_3439_2: {
     expect_stdout: "number"
 }
 
-cond_sequence_return: {
+cond_sequence_return_1: {
     options = {
         collapse_vars: true,
     }
@@ -6259,6 +6259,27 @@ cond_sequence_return: {
     expect_stdout: "2"
 }
 
+cond_sequence_return_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        console.log(function(n) {
+            var c = 0;
+            for (var k in [0, 1])
+                if (c += 1, k == n) return c;
+        }(1));
+    }
+    expect: {
+        console.log(function(n) {
+            var c = 0;
+            for (var k in [0, 1])
+                if (c += 1, k == n) return c;
+        }(1));
+    }
+    expect_stdout: "2"
+}
+
 issue_3520: {
     options = {
         collapse_vars: true,

test/mocha/cli.js

@@ -12,7 +12,9 @@ describe("bin/uglifyjs", function() {
     it("Should produce a functional build when using --self", function(done) {
         this.timeout(30000);
         var command = uglifyjscmd + ' --self -cm --wrap WrappedUglifyJS';
-        exec(command, function(err, stdout) {
+        exec(command, {
+            maxBuffer: 1048576
+        }, function(err, stdout) {
             if (err) throw err;
             eval(stdout);
             assert.strictEqual(typeof WrappedUglifyJS, "object");

test/mocha/spidermonkey.js

@@ -10,7 +10,9 @@ describe("spidermonkey export/import sanity test", function() {
         var command = uglifyjs + " --self -cm --wrap SpiderUglify -o spidermonkey | " +
             uglifyjs + " -p spidermonkey -cm";
 
-        exec(command, function(err, stdout) {
+        exec(command, {
+            maxBuffer: 1048576
+        }, function(err, stdout) {
             if (err) throw err;
 
             eval(stdout);