fix corner cases in functions & merge_vars (#4156)

fixes #4155

test/compress/functions.js

@@ -4777,3 +4777,34 @@ issue_4006: {
     }
     expect_stdout: "-1"
 }
+
+issue_4155: {
+    options = {
+        functions: true,
+        inline: true,
+        merge_vars: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function() {
+            var a;
+            (function() {
+                console.log(a);
+            })(a);
+            var b = function() {};
+            b && console.log(typeof b);
+        })();
+    }
+    expect: {
+        (function() {
+            void console.log(b);
+            var b = function() {};
+            b && console.log(typeof b);
+        })();
+    }
+    expect_stdout: [
+        "undefined",
+        "function",
+    ]
+}

test/compress/merge_vars.js

@@ -2822,3 +2822,41 @@ conditional_write: {
     }
     expect_stdout: "PASS,42"
 }
+
+issue_4155: {
+    options = {
+        inline: true,
+        merge_vars: true,
+    }
+    input: {
+        (function() {
+            try {
+                throw "PASS";
+            } catch (e) {
+                var a;
+                (function() {
+                    console.log(e, a);
+                })(a = NaN);
+            }
+            var e = function() {};
+            e && console.log(typeof e);
+        })();
+    }
+    expect: {
+        (function() {
+            try {
+                throw "PASS";
+            } catch (e) {
+                var a;
+                a = NaN,
+                void console.log(e, a);
+            }
+            var e = function() {};
+            e && console.log(typeof e);
+        })();
+    }
+    expect_stdout: [
+        "PASS NaN",
+        "function",
+    ]
+}