Introduce is_block_scope to AST_Node to determine block scope.

Will return false if AST_Node is instance of AST_Scope for now.

lib/ast.js

@@ -282,10 +282,9 @@ var AST_With = DEFNODE("With", "expression", {
 
 /* -----[ scope and functions ]----- */
 
-var AST_Scope = DEFNODE("Scope", "is_block_scope directives variables functions uses_with uses_eval parent_scope enclosed cname", {
+var AST_Scope = DEFNODE("Scope", "directives variables functions uses_with uses_eval parent_scope enclosed cname", {
     $documentation: "Base class for all statements introducing a lexical scope",
     $propdoc: {
-        is_block_scope: "[boolean] identifies a block scope",
         directives: "[string*/S] an array of directives declared in this scope",
         variables: "[Object/S] a map of name -> SymbolDef for all variables/functions defined in this scope",
         functions: "[Object/S] like `variables`, but only lists function declarations",
@@ -297,7 +296,7 @@ var AST_Scope = DEFNODE("Scope", "is_block_scope directives variables functions
     },
     get_defun_scope: function () {
         var self = this;
-        while (self.is_block_scope && self.parent_scope) {
+        while (self.is_block_scope() && self.parent_scope) {
             self = self.parent_scope;
         }
         return self;

lib/scope.js

@@ -110,15 +110,11 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
     var in_destructuring = null;
     var in_export;
     var tw = new TreeWalker(function(node, descend){
-        var create_a_block_scope =
+        if (node.is_block_scope()) {
-            (options.screw_ie8 && node instanceof AST_Catch) ||
-            ((node instanceof AST_Block) && node.creates_block_scope());
-        if (create_a_block_scope) {
             var save_scope = scope;
             scope = new AST_Scope(node);
             scope.init_scope_vars(nesting);
             scope.parent_scope = save_scope;
-            scope.is_block_scope = true;
             if (!(node instanceof AST_Scope)) {
                 scope.uses_with = save_scope.uses_with;
                 scope.uses_eval = save_scope.uses_eval;
@@ -188,7 +184,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             // instanceof AST_Scope) but we get to the symbol a bit
             // later.
             var parent_lambda = defun.parent_scope;
-            while (parent_lambda.is_block_scope) {
+            while (parent_lambda.is_block_scope()) {
                 parent_lambda = parent_lambda.parent_scope;
             }
             (node.scope = parent_lambda).def_function(node, in_export);
@@ -305,11 +301,16 @@ AST_Scope.DEFMETHOD("init_scope_vars", function(nesting){
     this.nesting = nesting;   // the nesting level of this scope (0 means toplevel)
 });
 
-AST_Block.DEFMETHOD("creates_block_scope", function() {
+AST_Node.DEFMETHOD("is_block_scope", function(){
+    return false; // Behaviour will be overridden by AST_Block
+});
+
+AST_Block.DEFMETHOD("is_block_scope", function(){
     return (
         !(this instanceof AST_Lambda) &&
         !(this instanceof AST_Toplevel) &&
-        !(this instanceof AST_Class)
+        !(this instanceof AST_Class) &&
+        !(this instanceof AST_SwitchBranch)
     );
 });
 

test/compress/block-scope.js

@@ -130,3 +130,45 @@ regression_block_scope_resolves: {
         }());
     }
 }
+
+switch_block_scope_mangler: {
+    mangle = {}
+    input: {
+        var fn = function(code) {
+            switch (code) {
+                case 1:
+                    let apple = code + 1;
+                    let dog = code + 4;
+                    console.log(apple, dog);
+                    break;
+                case 2:
+                    let banana = code + 2;
+                    console.log(banana);
+                    break;
+                default:
+                    let cat = code + 3;
+                    console.log(cat);
+            }
+        };
+    }
+    expect: {
+        var fn = function(o) {
+            switch (o) {
+              case 1:
+                let e = o + 1
+                let c = o + 4;
+                console.log(e, c);
+                break;
+
+              case 2:
+                let l = o + 2;
+                console.log(l);
+                break;
+
+              default:
+                let a = o + 3;
+                console.log(a);
+            }
+        };
+    }
+}