Added support for block scoping

README.md

@@ -437,6 +437,18 @@ contains `path.node`. See [scope.ts](lib/scope.ts) for its public
 interface, which currently includes `.isGlobal`, `.getGlobalScope()`,
 `.depth`, `.declares(name)`, `.lookup(name)`, and `.getBindings()`.
 
+A note on block scoping: As of ES2015 (ES6), variable declartions using `const` or `let` are block scoped. It also is the first ECMAScript spec to mention hoisting. However hoisting does not form part of the syntax, it is a runtime behaviour. Therefore `var` declarations are also scoped by block. For example:
+
+```javascript
+function x() {
+  var one = 1; // in x's scope
+  if (true) {
+    const two = 2; // in the if statement's scope
+    var three = 3;  // also in the if statement scope, but it's binding is hoisted and preinitialized at runtime
+  }
+}
+```
+
 Custom AST Node Types
 ---
 

lib/scope.ts

@@ -78,7 +78,14 @@ export default function scopePlugin(fork: Fork) {
 
     // In case you didn't know, the caught parameter shadows any variable
     // of the same name in an outer scope.
-    namedTypes.CatchClause
+    namedTypes.CatchClause,
+
+    // The following are statements that create block scopes
+    namedTypes.IfStatement,
+    namedTypes.ForStatement,
+    namedTypes.ForInStatement,
+    namedTypes.ForOfStatement,
+    namedTypes.TryStatement,
   ];
 
   var ScopeType = Type.or.apply(Type, scopeTypes);

test/ecmascript.ts

@@ -20,6 +20,7 @@ import {
   visit,
   defineMethod,
   astNodesAreEquivalent,
+  Visitor,
 } from "../main";
 import {
   babylonParse,
@@ -1313,6 +1314,108 @@ describe("scope methods", function () {
     assert.strictEqual(romVarDecl.declarations[0].id.name, "$1$0");
     assert.strictEqual(romVarDecl.declarations[1].id.name, "$1$1");
   });
+
+  const cases: Array<[string, Array<string>, Visitor]> = [
+    [
+      "if statement",
+      [
+        "  if (true) {",
+        "    const two = 2;",
+        "    var three = 3;",
+        "  }",
+      ],
+      {
+        visitIfStatement: function (path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['three', 'two'])
+          this.traverse(path)
+        }
+      },
+    ],
+    [
+      'for statement',
+      [
+        "  for (const two = 0; two < 2; two++) {",
+        "    const three = 3;",
+        "    var four = 4;",
+        "  }",
+      ],
+      {
+        visitForStatement: function (path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['four', 'three', 'two'])
+          this.traverse(path)
+        }
+      }
+    ],
+    [
+      'for in statement',
+      [
+        "  for (const two in [1,2,3]) {",
+        "    const three = 3;",
+        "    var four = 4;",
+        "  }",
+      ],
+      {
+        visitForInStatement: function(path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['four', 'three', 'two'])
+          this.traverse(path)
+        }
+      },
+    ],
+    [
+      'for of statement',
+      [
+        "  for (const two of [1,2,3]) {",
+        "    const three = 3;",
+        "    var four = 4;",
+        "  }",
+      ],
+      {
+        visitForOfStatement: function (path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['four', 'three', 'two'])
+          this.traverse(path)
+        }
+      },
+    ],
+    [
+      'try statement',
+      [
+        "  try {",
+        "    const two = 2;",
+        "    var three = 3;",
+        "  } catch(e) {}",
+      ],
+      {
+        visitTryStatement: function (path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['three', 'two'])
+          this.traverse(path)
+        }
+      },
+    ],
+  ];
+  cases.forEach(([desc, nestedScope, visitFns]) => {
+    it("getBindings - block scope - " + desc, () => {
+      var scope = [
+        "function x() {",
+        "  const one = 1;",
+        ...nestedScope,
+        "}"
+      ];
+      var ast = parse(scope.join("\n"));
+      visit(ast, {
+        visitFunctionDeclaration: function(path) {
+          const bindingNames = Object.keys(path.scope.getBindings()).sort()
+          assert.deepEqual(bindingNames, ['one'])
+          this.traverse(path)
+        },
+        ...visitFns,
+      })
+    })
+  })
 });
 
 describe("catch block scope", function() {