enhance join_vars & sequences (#2697)

- nudge declarations without assignments
  - within `AST_BlockStatement`
  - across `AST_If`

test/compress/conditionals.js

@@ -1203,3 +1203,24 @@ issue_2560: {
         "2",
     ]
 }
+
+hoist_decl: {
+    options = {
+        conditionals: true,
+        join_vars: true,
+        sequences: true,
+    }
+    input: {
+        if (x()) {
+            var a;
+            y();
+        } else {
+            z();
+            var b;
+        }
+    }
+    expect: {
+        var a, b;
+        x() ? y() : z();
+    }
+}

test/compress/functions.js

@@ -800,12 +800,12 @@ issue_2601_1: {
     expect: {
         var a = "FAIL";
         (function() {
+            var b;
             b = "foo",
             function(b) {
                 b && b();
             }(),
             b && (a = "PASS");
-            var b;
         })(),
         console.log(a);
     }

test/compress/sequences.js

@@ -796,3 +796,66 @@ cascade_assignment_in_return: {
         }
     }
 }
+
+hoist_defun: {
+    options = {
+        join_vars: true,
+        sequences: true,
+    }
+    input: {
+        x();
+        function f() {}
+        y();
+    }
+    expect: {
+        function f() {}
+        x(), y();
+    }
+}
+
+hoist_decl: {
+    options = {
+        join_vars: true,
+        sequences: true,
+    }
+    input: {
+        var a;
+        w();
+        var b = x();
+        y();
+        for (var c; 0;) z();
+        var d;
+    }
+    expect: {
+        var a;
+        w();
+        var b = x(), c, d;
+        for (y(); 0;) z();
+    }
+}
+
+for_init_var: {
+    options = {
+        join_vars: true,
+        unused: false,
+    }
+    input: {
+        var a = "PASS";
+        (function() {
+            var b = 42;
+            for (var c = 5; c > 0;) c--;
+            a = "FAIL";
+            var a;
+        })();
+        console.log(a);
+    }
+    expect: {
+        var a = "PASS";
+        (function() {
+            for (var b = 42, c = 5, a; c > 0;) c--;
+            a = "FAIL";
+        })();
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}