Avoid adding unnecessary closure for block scoping

packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js

@@ -1,6 +1,6 @@
 function wrapper(fn) {
   return (...args) => {
-    if (someCondition) {
+    while (someCondition) {
       const val = fn(...args);
       return val.test(() => {
         console.log(val);

packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js

@@ -2,17 +2,19 @@ function wrapper(fn) {
   return function () {
     var _arguments = arguments;
 
-    if (someCondition) {
-      var _ret = function () {
-        var val = fn(..._arguments);
-        return {
-          v: val.test(function () {
-            console.log(val);
-          })
-        };
-      }();
+    var _loop = function () {
+      var val = fn(..._arguments);
+      return {
+        v: val.test(function () {
+          console.log(val);
+        })
+      };
+    };
+
+    while (someCondition) {
+      var _ret = _loop();
 
       if (typeof _ret === "object") return _ret.v;
     }
   };
-}
+}

packages/babel-plugin-transform-es2015-block-scoping/src/index.js

@@ -112,8 +112,21 @@ function isVar(node) {
 }
 
 const letReferenceBlockVisitor = traverse.visitors.merge([{
+  Loop: {
+    enter(path, state) {
+      state.loopDepth++;
+    },
+    exit(path, state) {
+      state.loopDepth--;
+    },
+  },
   Function(path, state) {
-    path.traverse(letReferenceFunctionVisitor, state);
+    // References to block-scoped variables only require added closures if it's
+    // possible for the code to run more than once -- otherwise it is safe to
+    // simply rename the variables.
+    if (state.loopDepth > 0) {
+      path.traverse(letReferenceFunctionVisitor, state);
+    }
     return path.skip();
   }
 }, tdzVisitor]);
@@ -549,9 +562,19 @@ class BlockScoping {
     const state = {
       letReferences: this.letReferences,
       closurify:     false,
-      file:          this.file
+      file:          this.file,
+      loopDepth:     0,
     };
 
+    const loopOrFunctionParent = this.blockPath.find(
+      (path) => path.isLoop() || path.isFunction()
+    );
+    if (loopOrFunctionParent && loopOrFunctionParent.isLoop()) {
+      // There is a loop ancestor closer than the closest function, so we
+      // consider ourselves to be in a loop.
+      state.loopDepth++;
+    }
+
     // traverse through this block, stopping on functions and checking if they
     // contain any local let references
     this.blockPath.traverse(letReferenceBlockVisitor, state);

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js

@@ -1,11 +1,9 @@
 if (true) {
-  var x;
+  var foo = function () {};
 
-  (function () {
-    function foo() {}
-    function bar() {
-      return foo;
-    }
-    for (x in {}) {}
-  })();
+  var bar = function () {
+    return foo;
+  };
+
+  for (var x in {}) {}
 }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js

@@ -0,0 +1,34 @@
+function foo() {
+  const x = 5;
+  console.log(x);
+
+  {
+    const x = 7;
+    setTimeout(() => x, 0);
+  }
+}
+
+function bar() {
+  const x = 5;
+  console.log(x);
+
+  for (let i = 0; i < 7; i++) {
+    {
+      const x = i;
+      setTimeout(() => x, 0);
+    }
+  }
+}
+
+function baz() {
+  const x = 5;
+  console.log(x);
+
+  for (let i = 0; i < 7; i++) {
+    var qux = function qux(y) {
+      const x = y;
+      setTimeout(() => x, 0);
+    };
+    qux(i);
+  }
+}

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js

@@ -0,0 +1,42 @@
+function foo() {
+  var x = 5;
+  console.log(x);
+
+  {
+    var _x = 7;
+    setTimeout(function () {
+      return _x;
+    }, 0);
+  }
+}
+
+function bar() {
+  var x = 5;
+  console.log(x);
+
+  for (var i = 0; i < 7; i++) {
+    {
+      (function () {
+        var x = i;
+        setTimeout(function () {
+          return x;
+        }, 0);
+      })();
+    }
+  }
+}
+
+function baz() {
+  var x = 5;
+  console.log(x);
+
+  for (var i = 0; i < 7; i++) {
+    var qux = function qux(y) {
+      var x = y;
+      setTimeout(function () {
+        return x;
+      }, 0);
+    };
+    qux(i);
+  }
+}

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js

@@ -0,0 +1,11 @@
+var f1, f2;
+{
+  let z = 'z1 value';
+  f1 = function() { return z; };
+}
+{
+  let z = 'z2 value';
+  f2 = function() { return z; };
+}
+f1();
+f2();

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js

@@ -0,0 +1,15 @@
+var f1, f2;
+{
+  var z = 'z1 value';
+  f1 = function () {
+    return z;
+  };
+}
+{
+  var _z = 'z2 value';
+  f2 = function () {
+    return _z;
+  };
+}
+f1();
+f2();

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js

@@ -1,16 +1,18 @@
 function foo() {
-  switch (2) {
-    case 0: {
-      if (true) {
-        return;
-      }
+  while (true) {
+    switch (2) {
+      case 0: {
+        if (true) {
+          return;
+        }
 
-      const stuff = new Map();
-      const data = 0;
-      stuff.forEach(() => {
-        const d = data;
-      });
-      break;
+        const stuff = new Map();
+        const data = 0;
+        stuff.forEach(() => {
+          const d = data;
+        });
+        break;
+      }
     }
   }
 }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js

@@ -1,29 +1,31 @@
 function foo() {
-  switch (2) {
-    case 0:
-      {
-        var _ret = function () {
-          if (true) {
-            return {
-              v: void 0
-            };
-          }
+  while (true) {
+    switch (2) {
+      case 0:
+        {
+          var _ret = function () {
+            if (true) {
+              return {
+                v: void 0
+              };
+            }
 
-          var stuff = new Map();
-          var data = 0;
-          stuff.forEach(function () {
-            var d = data;
-          });
-          return "break";
-        }();
+            var stuff = new Map();
+            var data = 0;
+            stuff.forEach(function () {
+              var d = data;
+            });
+            return "break";
+          }();
 
-        switch (_ret) {
-          case "break":
-            break;
+          switch (_ret) {
+            case "break":
+              break;
 
-          default:
-            if (typeof _ret === "object") return _ret.v;
+            default:
+              if (typeof _ret === "object") return _ret.v;
+          }
         }
-      }
+    }
   }
 }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js

@@ -1,10 +1,12 @@
 function fn() {
-    switch (true) {
-    default:
-        let foo = 4;
-        if (true) {
-            let bar = () => foo;
-            console.log(bar());
+    while (true) {
+        switch (true) {
+        default:
+            let foo = 4;
+            if (true) {
+                let bar = () => foo;
+                console.log(bar());
+            }
         }
     }
 }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js

@@ -1,14 +1,16 @@
 function fn() {
-    (function () {
-        switch (true) {
-            default:
-                var foo = 4;
-                if (true) {
-                    var bar = function () {
-                        return foo;
-                    };
-                    console.log(bar());
-                }
-        }
-    })();
+    while (true) {
+        (function () {
+            switch (true) {
+                default:
+                    var foo = 4;
+                    if (true) {
+                        var bar = function () {
+                            return foo;
+                        };
+                        console.log(bar());
+                    }
+            }
+        })();
+    }
 }

packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js

@@ -0,0 +1,6 @@
+for (var i = 0; i < 5; i++) {
+  var l = i;
+  setTimeout(function () {
+    console.log(l);
+  }, 1);
+}

packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js

@@ -1,17 +1,11 @@
 function render(flag) {
   if (flag) {
-    var _ret = function () {
-      var bar = "bar";
+    var bar = "bar";
 
-      [].map(() => bar);
+    [].map(() => bar);
 
-      return {
-        v: <foo bar={bar} />
-      };
-    }();
-
-    if (typeof _ret === "object") return _ret.v;
+    return <foo bar={bar} />;
   }
 
   return null;
-}
+}