Block Switcher does not always show all Text block types

[hedgefield]

It confused me that the options you get in the Text block switcher are contextually limited. It makes sense that you cannot convert text into an image (or whatever non-text blocks there may be), but for example, if I have a Text block I get the option to turn it into a Quote/List/Formatted/Heading, but when it is a Heading, I can only change it to Text or Quote. Why is that?

[westonruter]

Each block can have a transforms property that defines how the block converts from and into other block types. For example:

• list: https://github.com/WordPress/gutenberg/blob/master/blocks/library/list/index.js#L79-L134
• preformatted:

  gutenberg/blocks/library/preformatted/index.js

  Lines 26 to 43 in 3037de6

  	transforms: {
  	from: [
  	{
  	type: 'block',
  	blocks: [ 'core/text' ],
  	transform: ( attributes ) =>
  	createBlock( 'core/preformatted', attributes ),
  	},
  	],
  	to: [
  	{
  	type: 'block',
  	blocks: [ 'core/text' ],
  	transform: ( attributes ) =>
  	createBlock( 'core/text', attributes ),
  	},
  	],
  	},

• heading:

  gutenberg/blocks/library/heading/index.js

  Lines 40 to 92 in 3037de6

  	transforms: {
  	from: [
  	{
  	type: 'block',
  	blocks: [ 'core/text' ],
  	transform: ( { content, ...attrs } ) => {
  	const isMultiParagraph = Array.isArray( content ) && isObject( content[ 0 ] ) && content[ 0 ].type === 'p';
  	if ( isMultiParagraph ) {
  	const headingContent = isObject( content[ 0 ] ) && content[ 0 ].type === 'p'
  	? content[ 0 ].props.children
  	: content[ 0 ];
  	const heading = createBlock( 'core/heading', {
  	content: headingContent,
  	} );
  	const blocks = [ heading ];
  	const remainingContent = content.slice( 1 );
  	if ( remainingContent.length ) {
  	const text = createBlock( 'core/text', {
  	...attrs,
  	content: remainingContent,
  	} );
  	blocks.push( text );
  	}
  	return blocks;
  	}
  	return createBlock( 'core/heading', {
  	content,
  	} );
  	},
  	},
  	{
  	type: 'raw',
  	matcher: ( node ) => /H\d/.test( node.nodeName ),
  	attributes: {
  	content: children( 'h1,h2,h3,h4,h5,h6' ),
  	nodeName: prop( 'h1,h2,h3,h4,h5,h6', 'nodeName' ),
  	},
  	},
  	],
  	to: [
  	{
  	type: 'block',
  	blocks: [ 'core/text' ],
  	transform: ( { content } ) => {
  	return createBlock( 'core/text', {
  	content,
  	} );
  	},
  	},
  	],
  	},

So if a block doesn't have a transforms definition to convert to the desired block, then the option won't be available, as I understand.

[hedgefield]

Gotcha, so if someone feels compelled to add a transform they can append those files with the 'conversion formula' so to speak?

[westonruter]

Yes, that's right. I'm pretty sure a plugin could add their own transforms to, say, the Text block by amending the object returned by wp.blocks.getBlockType('core/text').transforms.