fix blockHoist and declarations transformers unneccesarily unshifting use strict statements

lib/6to5/transformation/transformers/_block-hoist.js

@@ -1,3 +1,4 @@
+var useStrict = require("./use-strict");
 var _         = require("lodash");
 
 // Priority:
@@ -17,6 +18,7 @@ exports.Program = {
     }
     if (!hasChange) return;
 
+    useStrict._wrap(node, function () {
       var nodePriorities = _.groupBy(node.body, function (bodyNode) {
         var priority = bodyNode._blockHoist;
         if (priority == null) priority = 1;
@@ -25,5 +27,6 @@ exports.Program = {
       });
 
       node.body = _.flatten(_.values(nodePriorities).reverse());
+    });
   }
 };

lib/6to5/transformation/transformers/_declarations.js

@@ -1,3 +1,4 @@
+var useStrict = require("./use-strict");
 var t         = require("../../types");
 
 exports.secondPass = true;
@@ -7,6 +8,7 @@ exports.Program = function (node) {
   var kinds = {};
   var kind;
 
+  useStrict._wrap(node, function () {
     for (var i in node._declarations) {
       var declar = node._declarations[i];
 
@@ -24,6 +26,7 @@ exports.Program = function (node) {
     for (kind in kinds) {
       node.body.unshift(t.variableDeclaration(kind, kinds[kind]));
     }
+  });
 
   node._declarations = null;
 };

lib/6to5/transformation/transformers/use-strict.js

@@ -1,14 +1,27 @@
 var t = require("../../types");
 
+exports._has = function (node) {
+  var first = node.body[0];
+  return t.isExpressionStatement(first) && t.isLiteral(first.expression, { value: "use strict" });
+};
+
+exports._wrap = function (node, callback) {
+  var useStrictNode;
+  if (exports._has(node)) {
+    useStrictNode = node.body.shift();
+  }
+
+  callback();
+
+  if (useStrictNode) {
+    node.body.unshift(useStrictNode);
+  }
+};
+
 exports.ast = {
   exit: function (ast) {
-    var body = ast.program.body;
-    var first = body[0];
-
-    var noStrict = !first || !t.isExpressionStatement(first) || !t.isLiteral(first.expression) || first.expression.value !== "use strict";
-
-    if (noStrict) {
-      body.unshift(t.expressionStatement(t.literal("use strict")));
+    if (!exports._has(ast.program)) {
+      ast.program.body.unshift(t.expressionStatement(t.literal("use strict")));
     }
   }
 };