fix corner cases in switch and undefined (#1762)

- fix side effects in switch condition for singular blocks
- fix `undefined` confusion with local variable
- gate `OPT(AST_Switch)` with `switches`

fixes #1758
fixes #1759

5 files changed, 159 insertions, 15 deletions

diff --git a/lib/compress.js b/lib/compress.js
index fc11840d..5776fb88 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -77,6 +77,7 @@ function Compressor(options, false_by_default) {
         screw_ie8     : true,
         sequences     : !false_by_default,
         side_effects  : !false_by_default,
+        switches      : !false_by_default,
         top_retain    : null,
         toplevel      : !!(options && options["top_retain"]),
         unsafe        : false,
@@ -1054,7 +1055,7 @@ merge(Compressor.prototype, {
                         stat.value = cons_seq(stat.value);
                     }
                     else if (stat instanceof AST_Exit) {
-                        stat.value = cons_seq(make_node(AST_Undefined, stat));
+                        stat.value = cons_seq(make_node(AST_Undefined, stat).transform(compressor));
                     }
                     else if (stat instanceof AST_Switch) {
                         stat.expression = cons_seq(stat.expression);
@@ -2526,6 +2527,7 @@ merge(Compressor.prototype, {
     });
 
     OPT(AST_Switch, function(self, compressor){
+        if (!compressor.option("switches")) return self;
         var branch;
         var value = self.expression.evaluate(compressor);
         if (value !== self.expression) {
@@ -2599,7 +2601,15 @@ merge(Compressor.prototype, {
                     has_break = true;
             });
             self.walk(tw);
-            if (!has_break) return make_node(AST_BlockStatement, self, body[0]).optimize(compressor);
+            if (!has_break) {
+                body = body[0].body.slice();
+                body.unshift(make_node(AST_SimpleStatement, self.expression, {
+                    body: self.expression
+                }));
+                return make_node(AST_BlockStatement, self, {
+                    body: body
+                }).optimize(compressor);
+            }
         }
         return self;
 
@@ -2904,7 +2914,7 @@ merge(Compressor.prototype, {
                 if (name instanceof AST_SymbolRef
                     && name.name == "console"
                     && name.undeclared()) {
-                    return make_node(AST_Undefined, self).transform(compressor);
+                    return make_node(AST_Undefined, self).optimize(compressor);
                 }
             }
         }
diff --git a/test/compress/issue-1750.js b/test/compress/issue-1750.js
index 53a78e65..c1448afe 100644
--- a/test/compress/issue-1750.js
+++ b/test/compress/issue-1750.js
@@ -2,6 +2,7 @@ case_1: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         var a = 0, b = 1;
diff --git a/test/compress/reduce_vars.js b/test/compress/reduce_vars.js
index 87942ab9..cdc4ef20 100644
--- a/test/compress/reduce_vars.js
+++ b/test/compress/reduce_vars.js
@@ -1399,6 +1399,8 @@ issue_1670_1: {
         evaluate: true,
         dead_code: true,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
@@ -1429,6 +1431,8 @@ issue_1670_2: {
         dead_code: true,
         passes: 2,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
@@ -1458,6 +1462,8 @@ issue_1670_3: {
         evaluate: true,
         dead_code: true,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
@@ -1488,6 +1494,8 @@ issue_1670_4: {
         dead_code: true,
         passes: 2,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
@@ -1516,6 +1524,8 @@ issue_1670_5: {
         evaluate: true,
         keep_fargs: false,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
@@ -1544,6 +1554,8 @@ issue_1670_6: {
         evaluate: true,
         keep_fargs: false,
         reduce_vars: true,
+        side_effects: true,
+        switches: true,
         unused: true,
     }
     input: {
diff --git a/test/compress/sequences.js b/test/compress/sequences.js
index f1fa0e87..b3c54635 100644
--- a/test/compress/sequences.js
+++ b/test/compress/sequences.js
@@ -440,3 +440,29 @@ func_def_5: {
     }
     expect_stdout: "true"
 }
+
+issue_1758: {
+    options = {
+        sequences: true,
+        side_effects: true,
+    }
+    input: {
+        console.log(function(c) {
+            var undefined = 42;
+            return function() {
+                c--;
+                c--, c.toString();
+                return;
+            }();
+        }());
+    }
+    expect: {
+        console.log(function(c) {
+            var undefined = 42;
+            return function() {
+                return c--, c--, c.toString(), void 0;
+            }();
+        }());
+    }
+    expect_stdout: "undefined"
+}
diff --git a/test/compress/switch.js b/test/compress/switch.js
index 82d725f2..03c1e00a 100644
--- a/test/compress/switch.js
+++ b/test/compress/switch.js
@@ -1,5 +1,10 @@
 constant_switch_1: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1+1) {
           case 1: foo(); break;
@@ -13,7 +18,12 @@ constant_switch_1: {
 }
 
 constant_switch_2: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1) {
           case 1: foo();
@@ -28,7 +38,12 @@ constant_switch_2: {
 }
 
 constant_switch_3: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (10) {
           case 1: foo();
@@ -44,7 +59,12 @@ constant_switch_3: {
 }
 
 constant_switch_4: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (2) {
           case 1:
@@ -65,7 +85,12 @@ constant_switch_4: {
 }
 
 constant_switch_5: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         switch (1) {
           case 1:
@@ -94,7 +119,12 @@ constant_switch_5: {
 }
 
 constant_switch_6: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: {
             foo();
@@ -123,7 +153,12 @@ constant_switch_6: {
 }
 
 constant_switch_7: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: {
             foo();
@@ -161,7 +196,12 @@ constant_switch_7: {
 }
 
 constant_switch_8: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: switch (1) {
           case 1:
@@ -185,7 +225,12 @@ constant_switch_8: {
 }
 
 constant_switch_9: {
-    options = { dead_code: true, evaluate: true };
+    options = {
+        dead_code: true,
+        evaluate: true,
+        side_effects: true,
+        switches: true,
+    }
     input: {
         OUT: switch (1) {
           case 1:
@@ -210,7 +255,10 @@ constant_switch_9: {
 }
 
 drop_default_1: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz();
@@ -225,7 +273,10 @@ drop_default_1: {
 }
 
 drop_default_2: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz(); break;
@@ -241,7 +292,10 @@ drop_default_2: {
 }
 
 keep_default: {
-    options = { dead_code: true };
+    options = {
+        dead_code: true,
+        switches: true,
+    }
     input: {
         switch (foo) {
           case 'bar': baz();
@@ -263,6 +317,8 @@ issue_1663: {
     options = {
         dead_code: true,
         evaluate: true,
+        side_effects: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -294,6 +350,7 @@ issue_1663: {
 drop_case: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -312,6 +369,7 @@ drop_case: {
 keep_case: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -332,6 +390,7 @@ issue_376: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         switch (true) {
@@ -354,6 +413,7 @@ issue_376: {
 issue_441_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -381,6 +441,7 @@ issue_441_1: {
 issue_441_2: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (foo) {
@@ -414,6 +475,8 @@ issue_1674: {
     options = {
         dead_code: true,
         evaluate: true,
+        side_effects: true,
+        switches: true,
     }
     input: {
         switch (0) {
@@ -435,6 +498,7 @@ issue_1679: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -482,6 +546,7 @@ issue_1680_1: {
     options = {
         dead_code: true,
         evaluate: true,
+        switches: true,
     }
     input: {
         function f(x) {
@@ -522,6 +587,7 @@ issue_1680_1: {
 issue_1680_2: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         var a = 100, b = 10;
@@ -557,6 +623,7 @@ issue_1680_2: {
 issue_1690_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (console.log("PASS")) {}
@@ -570,6 +637,7 @@ issue_1690_1: {
 issue_1690_2: {
     options = {
         dead_code: false,
+        switches: true,
     }
     input: {
         switch (console.log("PASS")) {}
@@ -585,6 +653,7 @@ if_switch_typeof: {
         conditionals: true,
         dead_code: true,
         side_effects: true,
+        switches: true,
     }
     input: {
         if (a) switch(typeof b) {}
@@ -597,6 +666,7 @@ if_switch_typeof: {
 issue_1698: {
     options = {
         side_effects: true,
+        switches: true,
     }
     input: {
         var a = 1;
@@ -618,6 +688,7 @@ issue_1698: {
 issue_1705_1: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         var a = 0;
@@ -646,6 +717,7 @@ issue_1705_2: {
         reduce_vars: true,
         sequences: true,
         side_effects: true,
+        switches: true,
         toplevel: true,
         unused: true,
     }
@@ -666,6 +738,7 @@ issue_1705_2: {
 issue_1705_3: {
     options = {
         dead_code: true,
+        switches: true,
     }
     input: {
         switch (a) {
@@ -721,3 +794,25 @@ beautify: {
         "}",
     ]
 }
+
+issue_1758: {
+    options = {
+        dead_code: true,
+        switches: true,
+    }
+    input: {
+        var a = 1, b = 2;
+        switch (a--) {
+          default:
+            b++;
+        }
+        console.log(a, b);
+    }
+    expect: {
+        var a = 1, b = 2;
+        a--;
+        b++;
+        console.log(a, b);
+    }
+    expect_stdout: "0 3"
+}