Blockly: Headless Workspaces Require a Theme to Be Defined

[BeksOmega]

Problem statement

Headless workspaces require a theme to be defined, even though they are not rendered.

Expected Behavior

I can create themed blocks on a headless workspace.

Actual Behavior

I recieve an error.

Steps to Reproduce

1. Disable the changeTheme function of the playground.
2. Remove all of the code from the start function and replace it with the below:

  var altWorkspace = new Blockly.Workspace();
  // JSON block def.
  var block = new Blockly.Block(altWorkspace, 'controls_if');
  // JS block def.
  var block = new Blockly.Block(altWorkspace, 'text_getSubstring');

Stack Traces

block.js:1520 Block "controls_if": Style does not exist:  logic_blocks
  Blockly.Block.jsonInitStyle_ @ block.js:1520
  Blockly.Block.jsonInit @ block.js:1426
  (anonymous) @ blockly.js:414
  Blockly.Block @ block.js:181
  start @ playground.html:146
  onload @ playground.html:429

block.js:975 Uncaught Error: Trying to set block style to text_blocks before theme was defined via Blockly.setTheme().
    at Blockly.Block.setStyle (block.js:975)
    at Blockly.Block.init (text.js:224)
    at new Blockly.Block (block.js:181)
    at start (playground.html:147)
    at onload (playground.html:429)

Additional Information

Just noticed this when I was writing some unit tests, and thought I should send it in.

Oh I also noticed that colour functions (some of them my own additions) are defined on the block rather than the rendered block, not sure if this is intensional.

[alschmiedt]

I think this and #2540 are related

[kbruneel]

I have the same problem. Is there a workaround?

code:

var Blockly = require('node-blockly/browser');
var xml = Blockly.Xml.textToDom(xml_text);
var workspace = new Blockly.Workspace();
Blockly.Xml.domToWorkspace(xml, workspace);
var code = Blockly.JavaScript.workspaceToCode(workspace);

error:

Error: Trying to set block style to procedure_blocks before theme was defined via Blockly.setTheme().
    at module.exports.Blockly.Block.setStyle (blockly_compressed_browser.js:1460)
    at module.exports.Blockly.Block.init (blocks_compressed_browser.js:106)
    at new module.exports.Blockly.Block (blockly_compressed_browser.js:1440)
    at module.exports.Blockly.Workspace.newBlock (blockly_compressed_browser.js:1029)
    at Object.module.exports.Blockly.Xml.domToBlockHeadless_ (blockly_compressed_browser.js:993)
    at Object.module.exports.Blockly.Xml.domToBlock (blockly_compressed_browser.js:990)
    at Object.module.exports.Blockly.Xml.domToWorkspace (blockly_compressed_browser.js:986)

[kbruneel]

The following seems to work:

var Blockly = require('node-blockly/browser');
Blockly.setTheme(Blockly.Themes.Classic);