Require AST output to be opt-in, rather than opt-out.

packages/babel-core/src/transformation/index.js

@@ -64,7 +64,7 @@ export function runSync(
   return {
     metadata: file.metadata,
     options: opts,
-    ast: opts.ast !== false ? file.ast : null,
+    ast: opts.ast === true ? file.ast : null,
     code: outputCode === undefined ? null : outputCode,
     map: outputMap === undefined ? null : outputMap,
   };

packages/babel-core/test/api.js

@@ -34,6 +34,7 @@ describe("parser and generator options", function() {
 
   function newTransform(string) {
     return babel.transform(string, {
+      ast: true,
       parserOpts: {
         parser: recast.parse,
         plugins: ["flow"],
@@ -47,7 +48,10 @@ describe("parser and generator options", function() {
 
   it("options", function() {
     const string = "original;";
-    assert.deepEqual(newTransform(string).ast, babel.transform(string).ast);
+    assert.deepEqual(
+      newTransform(string).ast,
+      babel.transform(string, { ast: true }).ast,
+    );
     assert.equal(newTransform(string).code, string);
   });
 
@@ -57,6 +61,7 @@ describe("parser and generator options", function() {
     assert.deepEqual(
       newTransform(experimental).ast,
       babel.transform(experimental, {
+        ast: true,
         parserOpts: {
           plugins: ["flow"],
         },
@@ -66,6 +71,7 @@ describe("parser and generator options", function() {
 
     function newTransformWithPlugins(string) {
       return babel.transform(string, {
+        ast: true,
         plugins: [__dirname + "/../../babel-plugin-syntax-flow"],
         parserOpts: {
           parser: recast.parse,
@@ -79,6 +85,7 @@ describe("parser and generator options", function() {
     assert.deepEqual(
       newTransformWithPlugins(experimental).ast,
       babel.transform(experimental, {
+        ast: true,
         parserOpts: {
           plugins: ["flow"],
         },
@@ -93,6 +100,7 @@ describe("parser and generator options", function() {
     assert.notEqual(
       newTransform(experimental).ast,
       babel.transform(experimental, {
+        ast: true,
         parserOpts: {
           allowImportExportEverywhere: true,
         },
@@ -401,6 +409,18 @@ describe("api", function() {
     });
   });
 
+  it("ast option true", function() {
+    return transformAsync("foo('bar');", { ast: true }).then(function(result) {
+      assert.ok(result.ast);
+    });
+  });
+
+  it("ast option default", function() {
+    return transformAsync("foo('bar');").then(function(result) {
+      assert.ok(!result.ast);
+    });
+  });
+
   it("auxiliaryComment option", function() {
     return transformAsync("class Foo {}", {
       auxiliaryCommentBefore: "before",

packages/babel-plugin-transform-modules-commonjs/test/copied-nodes.js

@@ -5,6 +5,7 @@ test("Doesn't use the same object for two different nodes in the AST", function(
   const code = 'import Foo from "bar"; Foo; Foo;';
 
   const ast = babel.transform(code, {
+    ast: true,
     plugins: [[require("../"), { loose: true }]],
   }).ast;