Remove error throwing for svelte guarded features.

Adding the error is error prone due to the ability to include arbitrary
JS in conditionals, and provides a false sense of security due to the
fact that a deprecated feature flag could be used in many locations
other than a conditional.

This changes the strategy for svelte features to:

* **always** replace the imported deprecated flag with its boolean value
* **never** add an arbitrary error
* **always** remove feature source import statements that have no
  specifiers (previously only done in prod builds)

Author: Robert Jackson

fixtures/development-svelte-builds/expectation6.js

@@ -1,24 +1,28 @@
-import { DEPRECATED_PARTIALS, DEPRECATED_CONTROLLERS } from '@ember/features';
 
-export let PartialComponentManager;
-if (DEPRECATED_PARTIALS) {
-  throw new Error('You indicated you don\'t have any deprecations, however you are relying on DEPRECATED_PARTIALS.');
 
+export let PartialComponentManager;
+if (false /* DEPRECATED_PARTIALS */) {
   PartialComponentManager = class {
     constructor() {
       this.isDone = true;
     }
   };
 }
 
-if (DEPRECATED_PARTIALS && someOtherThing()) {
-  throw new Error('You indicated you don\'t have any deprecations, however you are relying on DEPRECATED_PARTIALS.');
-
+if (false /* DEPRECATED_PARTIALS */ && someOtherThing()) {
   doStuff();
 }
 
+if (!false /* DEPRECATED_PARTIALS */ && someOtherThing()) {
+  doStuff2();
+}
+
+if (false /* DEPRECATED_PARTIALS */ === false && someOtherThing()) {
+  doStuff3();
+}
+
 export let ObjectController;
-if (DEPRECATED_CONTROLLERS) {
+if (true /* DEPRECATED_CONTROLLERS */) {
   ObjectController = class {
     constructor() {
       this.isDoneAsWell = true;

fixtures/development-svelte-builds/expectation7.js

@@ -1,8 +1,8 @@
-import { DEPRECATED_PARTIALS, DEPRECATED_CONTROLLERS } from '@ember/features';
 export let PartialComponentManager;
 
-if (DEPRECATED_PARTIALS) {
-  throw new Error("You indicated you don't have any deprecations, however you are relying on DEPRECATED_PARTIALS.");
+if (false
+/* DEPRECATED_PARTIALS */
+) {
   PartialComponentManager = class {
     constructor() {
       this.isDone = true;
@@ -11,14 +11,29 @@ if (DEPRECATED_PARTIALS) {
   };
 }
 
-if (DEPRECATED_PARTIALS && someOtherThing()) {
-  throw new Error("You indicated you don't have any deprecations, however you are relying on DEPRECATED_PARTIALS.");
+if (false
+/* DEPRECATED_PARTIALS */
+&& someOtherThing()) {
   doStuff();
 }
 
+if (!false
+/* DEPRECATED_PARTIALS */
+&& someOtherThing()) {
+  doStuff2();
+}
+
+if (false
+/* DEPRECATED_PARTIALS */
+=== false && someOtherThing()) {
+  doStuff3();
+}
+
 export let ObjectController;
 
-if (DEPRECATED_CONTROLLERS) {
+if (true
+/* DEPRECATED_CONTROLLERS */
+) {
   ObjectController = class {
     constructor() {
       this.isDoneAsWell = true;

fixtures/development-svelte-builds/sample.js

@@ -13,6 +13,14 @@ if (DEPRECATED_PARTIALS && someOtherThing()) {
   doStuff();
 }
 
+if (!DEPRECATED_PARTIALS && someOtherThing()) {
+  doStuff2();
+}
+
+if (DEPRECATED_PARTIALS === false && someOtherThing()) {
+  doStuff3();
+}
+
 export let ObjectController;
 if (DEPRECATED_CONTROLLERS) {
   ObjectController = class {

fixtures/production-svelte-builds/expectation6.js

@@ -1,20 +1,20 @@
 
 
 export let PartialComponentManager;
-if (false) {
+if (false /* DEPRECATED_PARTIALS */) {
   PartialComponentManager = class {
     constructor() {
       this.isDone = true;
     }
   };
 }
 
-if (false && someOtherThing()) {
+if (false /* DEPRECATED_PARTIALS */ && someOtherThing()) {
   doStuff();
 }
 
 export let ObjectController;
-if (true) {
+if (true /* DEPRECATED_CONTROLLERS */) {
   ObjectController = class {
     constructor() {
       this.isDoneAsWell = true;

fixtures/production-svelte-builds/expectation7.js

@@ -1,6 +1,8 @@
 export let PartialComponentManager;
 
-if (false) {
+if (false
+/* DEPRECATED_PARTIALS */
+) {
   PartialComponentManager = class {
     constructor() {
       this.isDone = true;
@@ -9,13 +11,17 @@ if (false) {
   };
 }
 
-if (false && someOtherThing()) {
+if (false
+/* DEPRECATED_PARTIALS */
+&& someOtherThing()) {
   doStuff();
 }
 
 export let ObjectController;
 
-if (true) {
+if (true
+/* DEPRECATED_CONTROLLERS */
+) {
   ObjectController = class {
     constructor() {
       this.isDoneAsWell = true;

src/index.js

@@ -5,8 +5,6 @@ const Macros = require('./utils/macros');
 const normalizeOptions = require('./utils/normalize-options').normalizeOptions;
 
 function macros(babel) {
-  const t = babel.types;
-
   let options;
 
   return {
@@ -15,7 +13,7 @@ function macros(babel) {
       Program: {
         enter(path, state) {
           options = normalizeOptions(state.opts);
-          this.macroBuilder = new Macros(t, options);
+          this.macroBuilder = new Macros(babel, options);
 
           let body = path.get('body');
 

src/utils/macros.js

@@ -6,7 +6,8 @@ const DEBUG = 'DEBUG';
 const SUPPORTED_MACROS = ['assert', 'deprecate', 'warn', 'log'];
 
 module.exports = class Macros {
-  constructor(t, options) {
+  constructor(babel, options) {
+    this.babel = babel;
     this.localDebugBindings = [];
     this.envFlagBindings = [];
     this.hasEnvFlags = false;
@@ -19,7 +20,7 @@ module.exports = class Macros {
     this.svelteVersions = options.svelte;
     this.featureFlags = options.features || [];
     this.debugHelpers = options.externalizeHelpers || {};
-    this.builder = new Builder(t, {
+    this.builder = new Builder(babel.types, {
       module: this.debugHelpers.module,
       global: this.debugHelpers.global,
       assertPredicateIndex: options.debugTools.assertPredicateIndex,
@@ -88,43 +89,42 @@ module.exports = class Macros {
 
   _inlineSvelteFlags(path) {
     let svelteMap = this.svelteMap;
-    let envFlags = this.envFlags;
-    let builder = this.builder;
+    let t = this.babel.types;
+
+    function buildIdentifier(value, name) {
+      let replacement = t.booleanLiteral(value);
+
+      // when we only support babel@7 we should change this
+      // to `path.addComment` or `t.addComment`
+      let comment = {
+        type: 'CommentBlock',
+        value: ` ${name} `,
+        leading: false,
+        trailing: true,
+      };
+      replacement.trailingComments = [comment];
+
+      return replacement;
+    }
 
     let sources = Object.keys(svelteMap);
     sources.forEach(source => {
-      Object.keys(svelteMap[source]).forEach(flag => {
+      let flagsForSource = svelteMap[source];
+
+      for (let flag in flagsForSource) {
+        let flagValue = flagsForSource[flag];
+
         let binding = path.scope.getBinding(flag);
         if (binding !== undefined) {
           binding.referencePaths.forEach(p => {
-            let t = builder.t;
-            // in debug builds add an error after a conditional (to ensure if the
-            // specific branch is taken, an error is thrown)
-            if (envFlags.DEBUG && svelteMap[source][flag] === false) {
-              let parentIfStatement = p.find(p => p.isIfStatement());
-              if (parentIfStatement) {
-                let consequent = parentIfStatement.get('consequent');
-                consequent.unshiftContainer(
-                  'body',
-                  t.throwStatement(
-                    t.newExpression(t.identifier('Error'), [
-                      t.stringLiteral(
-                        `You indicated you don't have any deprecations, however you are relying on ${flag}.`
-                      ),
-                    ])
-                  )
-                );
-              }
-            } else if (envFlags.DEBUG === false) {
-              p.replaceWith(t.booleanLiteral(svelteMap[source][flag]));
-            }
+            let replacement = buildIdentifier(flagValue, flag);
+
+            p.replaceWith(replacement);
           });
 
-          if (!envFlags.DEBUG && binding) {
-            binding.path.remove();
-          }
+          binding.path.remove();
         }
-      });
+      }
     });
   }
 
@@ -183,19 +183,17 @@ module.exports = class Macros {
   _cleanImports(path) {
     let body = path.get('body');
 
-    if (!this.envFlags.DEBUG) {
-      for (let i = 0; i < body.length; i++) {
-        let decl = body[i];
-
-        if (this.builder.t.isImportDeclaration(decl)) {
-          let source = decl.node.source.value;
-          if (this.featureSources.indexOf(source) > -1) {
-            if (decl.node.specifiers.length > 0) {
-              this._detectForeignFeatureFlag(decl.node.specifiers, source);
-            } else {
-              decl.remove();
-              break;
-            }
+    for (let i = 0; i < body.length; i++) {
+      let decl = body[i];
+
+      if (this.builder.t.isImportDeclaration(decl)) {
+        let source = decl.node.source.value;
+        if (this.featureSources.indexOf(source) > -1) {
+          if (decl.node.specifiers.length > 0) {
+            this._detectForeignFeatureFlag(decl.node.specifiers, source);
+          } else {
+            decl.remove();
+            break;
           }
         }
       }