enhance unsafe (#5903)

Author: alexlamsl

lib/compress.js

@@ -12642,6 +12642,7 @@ Compressor.prototype.compress = function(node) {
         }
 
         function is_indexFn(node) {
+            while (node instanceof AST_Assign && node.operator == "=") node = node.right;
             return node.TYPE == "Call"
                 && node.expression instanceof AST_Dot
                 && indexFns[node.expression.property];

test/compress/comparisons.js

@@ -471,6 +471,28 @@ unsafe_indexOf: {
     ]
 }
 
+unsafe_indexOf_assignment: {
+    options = {
+        booleans: true,
+        comparisons: true,
+        unsafe: true,
+    }
+    input: {
+        var a;
+        if ((a = Object.keys({ foo: 42 }).indexOf("bar")) < 0) console.log("PASS");
+        if (0 > (a = Object.keys({ foo: 42 }).indexOf("bar"))) console.log("PASS");
+    }
+    expect: {
+        var a;
+        if (!~(a = Object.keys({ foo: 42 }).indexOf("bar"))) console.log("PASS");
+        if (!~(a = Object.keys({ foo: 42 }).indexOf("bar"))) console.log("PASS");
+    }
+    expect_stdout: [
+        "PASS",
+        "PASS",
+    ]
+}
+
 issue_3413: {
     options = {
         comparisons: true,