Fix setValue not handling block disposal (#3766)

core/field.js

@@ -858,16 +858,20 @@ Blockly.Field.prototype.setValue = function(newValue) {
       return;
     }
   }
+  var source = this.sourceBlock_;
+  if (source && source.disposed) {
+    doLogging && console.log('source disposed, return');
+    return;
+  }
   var oldValue = this.getValue();
   if (oldValue === newValue) {
     doLogging && console.log('same, return');
-    // No change.
     return;
   }
 
-  if (this.sourceBlock_ && Blockly.Events.isEnabled()) {
+  if (source && Blockly.Events.isEnabled()) {
     Blockly.Events.fire(new Blockly.Events.BlockChange(
-        this.sourceBlock_, 'field', this.name || null, oldValue, newValue));
+        source, 'field', this.name || null, oldValue, newValue));
   }
   this.doValueUpdate_(newValue);
   if (this.isDirty_) {

tests/blocks/test_blocks.js

@@ -1343,6 +1343,22 @@ Blockly.Blocks['test_images_clickhandler'] = {
   }
 };
 
+Blockly.Blocks['test_validators_dispose_block'] = {
+  init: function() {
+    this.appendDummyInput()
+        .appendField("dispose block")
+        .appendField(new Blockly.FieldTextInput("default", this.validate), "INPUT");
+    this.setColour(230);
+    this.setCommentText('Any changes to the text cause the block to be disposed');
+  },
+
+  validate: function(newValue) {
+    if (newValue != "default") {
+      this.getSourceBlock().dispose(true);
+    }
+  }
+};
+
 Blockly.Blocks['test_validators_text_null'] = {
   init: function() {
     this.appendDummyInput()

tests/playground.html

@@ -1677,6 +1677,9 @@ var spaghettiXml = [
         <button text="add blocks to workspace" callbackKey="addAllBlocksToWorkspace"></button>
         <sep gap="8"></sep>
         <button text="set input" callbackKey="setInput"></button>
+        <label text="Dispose block"></label>
+        <sep gap="12"></sep>
+        <block type="test_validators_dispose_block"></block>
         <label text="Angles"></label>
         <sep gap="12"></sep>
         <block type="test_validators_angle_null"></block>