From 22e79ae49617e7fe655a46f473e564396ee200f5 Mon Sep 17 00:00:00 2001
From: Monica Kozbial <kozbial@google.com>
Date: Thu, 26 Sep 2019 13:23:45 -0700
Subject: [PATCH] Updating behavior of register functions and adding
 unregister. (#3085)

* Updating behavior of register functions and adding unregister.

* Updates jsdoc comments.
---
 core/extensions.js                       | 13 +++++++++++++
 core/field_registry.js                   | 23 ++++++++++++++++++++---
 core/renderers/common/block_rendering.js | 13 +++++++++++++
 tests/mocha/field_registry_test.js       |  6 +++---
 4 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/core/extensions.js b/core/extensions.js
index 938f7c684..1f19a087d 100644
--- a/core/extensions.js
+++ b/core/extensions.js
@@ -128,6 +128,19 @@ Blockly.Extensions.registerMutator = function(name, mixinObj, opt_helperFn,
   });
 };
 
+/**
+ * Unregisters the extension registered with the given name.
+ * @param {string} name The name of the extension to unregister.
+ */
+Blockly.Extensions.unregister = function(name) {
+  if (Blockly.Extensions.ALL_[name]) {
+    Blockly.Extensions.ALL_[name] = undefined;
+  } else {
+    console.warn('No extension mapping for name "' + name +
+        '" found to unregister');
+  }
+};
+
 /**
  * Applies an extension method to a block. This should only be called during
  * block construction.
diff --git a/core/field_registry.js b/core/field_registry.js
index 7556bd0d6..c20be98b7 100644
--- a/core/field_registry.js
+++ b/core/field_registry.js
@@ -38,20 +38,24 @@ goog.provide('Blockly.fieldRegistry');
 Blockly.fieldRegistry.typeMap_ = {};
 
 /**
- * Registers a field type. May also override an existing field type.
+ * Registers a field type.
  * Blockly.fieldRegistry.fromJson uses this registry to
  * find the appropriate field type.
  * @param {string} type The field type name as used in the JSON definition.
  * @param {!{fromJson: Function}} fieldClass The field class containing a
  *     fromJson function that can construct an instance of the field.
- * @throws {Error} if the type name is empty, or the fieldClass is not an
- *     object containing a fromJson function.
+ * @throws {Error} if the type name is empty, the field is already
+ *     registered, or the fieldClass is not an object containing a fromJson
+ *     function.
  */
 Blockly.fieldRegistry.register = function(type, fieldClass) {
   if ((typeof type != 'string') || (type.trim() == '')) {
     throw Error('Invalid field type "' + type + '". The type must be a' +
       ' non-empty string.');
   }
+  if (Blockly.fieldRegistry.typeMap_[type]) {
+    throw Error('Error: Field "' + type + '" is already registered.');
+  }
   if (!fieldClass || (typeof fieldClass.fromJson != 'function')) {
     throw Error('Field "' + fieldClass + '" must have a fromJson function');
   }
@@ -59,6 +63,19 @@ Blockly.fieldRegistry.register = function(type, fieldClass) {
   Blockly.fieldRegistry.typeMap_[type] = fieldClass;
 };
 
+/**
+ * Unregisters the field registered with the given type.
+ * @param {string} type The field type name as used in the JSON definition.
+ */
+Blockly.fieldRegistry.unregister = function(type) {
+  if (Blockly.fieldRegistry.typeMap_[type]) {
+    Blockly.fieldRegistry.typeMap_[type] = undefined;
+  } else {
+    console.warn('No field mapping for type "' + type +
+        '" found to unregister');
+  }
+};
+
 /**
  * Construct a Field from a JSON arg object.
  * Finds the appropriate registered field by the type name as registered using
diff --git a/core/renderers/common/block_rendering.js b/core/renderers/common/block_rendering.js
index 353936e08..f476d1400 100644
--- a/core/renderers/common/block_rendering.js
+++ b/core/renderers/common/block_rendering.js
@@ -61,6 +61,19 @@ Blockly.blockRendering.register = function(name, rendererClass) {
   Blockly.blockRendering.rendererMap_[name] = rendererClass;
 };
 
+/**
+ * Unregisters the renderer registered with the given name.
+ * @param {string} name The name of the renderer.
+ */
+Blockly.blockRendering.unregister = function(name) {
+  if (Blockly.blockRendering.rendererMap_[name]) {
+    Blockly.blockRendering.rendererMap_[name] = undefined;
+  } else {
+    console.warn('No renderer mapping for name "' + name +
+        '" found to unregister');
+  }
+};
+
 /**
  * Turn on the blocks debugger.
  * @package
diff --git a/tests/mocha/field_registry_test.js b/tests/mocha/field_registry_test.js
index 7f636f540..7f1e4574e 100644
--- a/tests/mocha/field_registry_test.js
+++ b/tests/mocha/field_registry_test.js
@@ -57,11 +57,11 @@ suite('Field Registry', function() {
         Blockly.fieldRegistry.register(CustomFieldType.fromJson, '');
       }, 'Invalid field type');
     });
-    // TODO (#2788): What do you want it to do if you overwrite a key?
     test('Overwrite a Key', function() {
       Blockly.fieldRegistry.register('field_custom_test', CustomFieldType);
-
-      Blockly.fieldRegistry.register('field_custom_test', CustomFieldType);
+      chai.assert.throws(function() {
+        Blockly.fieldRegistry.register('field_custom_test', CustomFieldType);
+      }, 'already registered');
     });
     test('Null Value', function() {
       chai.assert.throws(function() {