fix corner case in keep_fargs (#3424)

fixes #3423

lib/compress.js

@@ -108,7 +108,7 @@ function Compressor(options, false_by_default) {
     this.drop_fargs = keep_fargs == "strict" ? function(lambda, parent) {
         if (lambda.length_read) return false;
         var name = lambda.name;
-        if (!name) return parent && parent.TYPE == "Call";
+        if (!name) return parent && parent.TYPE == "Call" && parent.expression === lambda;
         if (name.fixed_value() !== lambda) return false;
         var def = name.definition();
         if (def.direct_access) return false;

test/compress/keep_fargs.js

@@ -1117,3 +1117,41 @@ issue_3420_3: {
     }
     expect_stdout: "4"
 }
+
+issue_3423_1: {
+    options = {
+        keep_fargs: "strict",
+        unused: true,
+    }
+    input: {
+        function f(g) {
+            console.log(g.length);
+        }
+        f(function(a) {});
+    }
+    expect: {
+        function f(g) {
+            console.log(g.length);
+        }
+        f(function(a) {});
+    }
+    expect_stdout: "1"
+}
+
+issue_3423_2: {
+    options = {
+        keep_fargs: "strict",
+        unused: true,
+    }
+    input: {
+        new function(a) {
+            console.log(this.constructor.length);
+        }();
+    }
+    expect: {
+        new function(a) {
+            console.log(this.constructor.length);
+        }();
+    }
+    expect_stdout: "1"
+}