add type inferrence that expires when a binding is reassigned

lib/6to5/traversal/scope.js

@@ -185,16 +185,24 @@ Scope.prototype.inferType = function (node) {
     target = node.init;
   }
 
+  if (t.isArrayExpression(target)) {
+    return t.genericTypeAnnotation(t.identifier("Array"));
+  }
+
+  if (t.isObjectExpression(target)) {
+    return;
+  }
+
+  if (t.isLiteral(target)) {
+    return;
+  }
+
   if (t.isCallExpression(target)) {
     // todo: resolve this to a return type
   }
 
-  if (t.isMemberExpression(target)) {
-    // todo: crawl this and find the correct type, bail on anything that we cannot possibly be 100% confident on
-  }
-
   if (t.isIdentifier(target)) {
-    // todo
+    return;
   }
 };
 
@@ -217,7 +225,12 @@ Scope.prototype.assignType = function (name, type) {
   info.identifier.typeAnnotation = info.typeAnnotation = type;
 };
 
-Scope.prototype.getTypeAnnotation = function (key, id, node) {
+Scope.prototype.getTypeAnnotation = function (name, id, node) {
+  var info = {
+    annotation: null,
+    inferred: false
+  };
+
   var type;
 
   if (id.typeAnnotation) {
@@ -225,13 +238,16 @@ Scope.prototype.getTypeAnnotation = function (key, id, node) {
   }
 
   if (!type) {
+    info.inferred = true;
     type = this.inferType(node);
   }
 
   if (type) {
     if (t.isTypeAnnotation(type)) type = type.typeAnnotation;
-    return type;
+    info.annotation = type;
   }
+
+  return info;
 };
 
 Scope.prototype.toArray = function (node, i) {
@@ -284,7 +300,14 @@ Scope.prototype.registerBindingReassignment = function (node) {
   var ids = t.getBindingIdentifiers(node);
   for (var name in ids) {
     var info = this.getBindingInfo(name);
-    if (info) info.reassigned = true;
+    if (info) {
+      info.reassigned = true;
+
+      if (info.typeAnnotationInferred) {
+        // destroy the inferred typeAnnotation
+        info.typeAnnotation = null;
+      }
+    }
   }
 };
 
@@ -298,12 +321,15 @@ Scope.prototype.registerBinding = function (kind, node) {
 
     this.checkBlockScopedCollisions(kind, name, id);
 
+    var typeInfo = this.getTypeAnnotation(name, id, node);
+
     this.bindings[name] = {
-      typeAnnotation: this.getTypeAnnotation(name, id, node),
-      reassigned:     false,
-      identifier:     id,
-      scope:          this,
-      kind:           kind
+      typeAnnotationInferred: typeInfo.inferred,
+      typeAnnotation:         typeInfo.annotation,
+      reassigned:             false,
+      identifier:             id,
+      scope:                  this,
+      kind:                   kind
     };
   }
 };