Crash if a field click deletes a block

[maribethb]

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• I have searched for similar issues before opening a new one.

Description

If you have a block with a field that deletes the block*, Blockly will crash because the gesture handling code assumes the block continues to exist.

We can fix this in several ways:

1. Move bringBlockToFront to the beginning of doFieldClick (so that it happens before the field has a chance to handle the click)
2. Have bringBlockToFront make sure disposed is false on the block before calling the bringToFront method. This would prevent trying to move a dead/dying block.

Reproduction steps

1. Add the following block definition to the playground above the start call.

Blockly.Blocks['test'] = {
        init: function() {
          this.setStyle('math_blocks');
          this.appendDummyInput()
              .appendField(new Blockly.FieldImage(
                  'media/arrow.png',
                  30,
                  30,
                  'test',
                  function() {
                    this.getSourceBlock().dispose();
                  }
              ));
        }

2. Run npm run start to start the playground.
3. Load the following JSON into the playground:

{
  "blocks": {
    "languageVersion": 0,
    "blocks": [
      {
        "type": "test"
      }
    ]
  }
}

4. Open the browser.
5. Click the arrow on the block.
6. Observe the error in the console.

Stack trace

Uncaught TypeError: Cannot read properties of null (reading 'childNodes')
    at BlockSvg$$module$build$src$core$block_svg.bringToFront (block_svg.ts:1227:34)
    at Gesture$$module$build$src$core$gesture.bringBlockToFront_ (gesture.ts:940:25)
    at Gesture$$module$build$src$core$gesture.doFieldClick_ (gesture.ts:880:10)
    at Gesture$$module$build$src$core$gesture.handleUp (gesture.ts:591:14)
    at HTMLDocument.g (browser_events.ts:70:9)

Additional Info

This should also be fixed for icons since, #7588 is fixed.

To Fix

1. Run the reproduction steps above to make sure you can reproduce the issue.
2. Add a check in bringToFront that checks if this.isDeadOrDying(), and returns early if so.
3. Run the reproduction steps again to make sure the issue doesn't reproduce.

[Apoorvgarg-creator]

Interested to solve the issue

[maribethb]

Great, I'll assign you @Apoorvgarg-creator ! If you have any questions please feel free to ask here.

[Apoorvgarg-creator]

Great, I'll assign you @Apoorvgarg-creator ! If you have any questions please feel free to ask here.

Thank you !

[Apoorvgarg-creator]

@maribethb I am working on this issue, I cloned the repo and ran npm i after that I want to build and reproduce the issue, can you please help me !

[Apoorvgarg-creator]

Getting this on running npm run start

[BeksOmega]

Getting this on running npm run start

Looks like you're probably using an old version of node. Can you upgrade to Node v20 @Apoorvgarg-creator and see if that fixes the issue?

[Apoorvgarg-creator]

@BeksOmega Thank you, It worked !

I was able to reproduce the error. Solving the issue. Thank you !!

[Apoorvgarg-creator]

@maribethb @BeksOmega I have solved the bug with the solution proposed in the issue.
But I wanted to know if this solution is also logically correct or not -
if I add parent !== null check before accessing properties of parent ?