fix corner case in evaluate (#5357)

fixes #5356

lib/compress.js

@@ -4404,9 +4404,15 @@ Compressor.prototype.compress = function(node) {
         def(AST_Sequence, function(compressor) {
             return this.tail_node().is_number(compressor);
         });
-        def(AST_SymbolRef, function(compressor) {
+        def(AST_SymbolRef, function(compressor, keep_unary) {
             var fixed = this.fixed_value();
             if (!fixed) return false;
+            if (keep_unary
+                && fixed instanceof AST_UnaryPrefix
+                && fixed.operator == "+"
+                && fixed.expression.equivalent_to(this)) {
+                return false;
+            }
             this.is_number = return_false;
             var result = fixed.is_number(compressor);
             delete this.is_number;
@@ -10772,7 +10778,7 @@ Compressor.prototype.compress = function(node) {
         }
         switch (op) {
           case "+":
-            if (compressor.option("evaluate") && exp.is_number(compressor)) return exp;
+            if (compressor.option("evaluate") && exp.is_number(compressor, true)) return exp;
             break;
           case "-":
             if (exp instanceof AST_Infinity) exp = exp.transform(compressor);

test/compress/arrows.js

@@ -1002,3 +1002,19 @@ issue_5342_2: {
     expect_stdout: "undefined"
     node_version: ">=4"
 }
+
+issue_5356: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log((a => a++)(console));
+    }
+    expect: {
+        console.log((a => +a)(console));
+    }
+    expect_stdout: "NaN"
+    node_version: ">=4"
+}

test/compress/evaluate.js

@@ -3273,3 +3273,24 @@ issue_5354: {
     }
     expect_stdout: "number string number"
 }
+
+issue_5356: {
+    options = {
+        evaluate: true,
+        inline: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        console.log(function() {
+            return a++;
+            var a = a;
+        }());
+    }
+    expect: {
+        console.log(+a);
+        var a;
+    }
+    expect_stdout: "NaN"
+}