Edit Post: Select blocks only once multiple verified

[aduth]

Related: #5031

This pull request seeks to optimize the multiple-use validation to avoid calling the getBlocks selector until after verifying that a non-multiple-supporting block is present in the post. This should help alleviate some performance bottleneck for a currently-underperforming selector (getBlocks), particularly when the the condition will not apply for the vast majority of blocks.

This is effectively a refactoring to reorganize code to only assign a variable value at a point where it is certain to be relevant for use by the remainder of the function. As an aside, it would be very interesting to try to develop a lint rule to verify that a variable is used before the next return statement.

Testing instructions:

Repeat testing instructions from #5031

Add a console.count at the point the getBlocks function is called, and verify that it is not called while authoring paragraph content (unlike before).

[jorgefilipecosta]

Looks good in my tests, as expected no behavior changes were noticed 👍
As referred, this would for sure be an excellent lint rule. Maybe it was already implemented by someone and is available.
The end 2 end tests fail seems totally unrelated and an intermittent problem, I restarted them.

[aduth]

As referred, this would for sure be an excellent lint rule. Maybe it was already implemented by someone and is available.

I looked around a bit, and unfortunately couldn't find much. I started working on a rule, and found a few edge cases, mostly stylistic:

• We often destructure-assign a variable which may not be used before the return (example)
  • Solution Exempt destructuring?
• Sometimes it's not a "big deal" to assign a variable (example)
  • Solution: Limit to expensive operations; namely when initialized to CallExpression (a function call)?

Here's my work-in-progress:

https://astexplorer.net/#/gist/dc29d9096eac1664d8eb287139fa55ac/94f70e52c05456e1092f3109e5f882d60b68f076

It finds a lot of very interesting faults!

Full report

/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/bin/packages/watch.js
  40:5  error  Assigned variable `filePath` needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/block-library/src/cover/index.js

329:5  error  Assigned variable classes needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/block-library/src/image/edit.js

419:4  error  Assigned variable imageSizeOptions needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/blocks/src/api/factory.js

125:3  error  Assigned variable sourceBlock needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

131:3  error  Assigned variable sourceBlock needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/blocks/src/api/serializer.js

271:4  error  Assigned variable saveAttributes needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/core-data/src/queried-data/selectors.js

33:3  error  Assigned variable page needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

33:3  error  Assigned variable perPage needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

38:3  error  Assigned variable page needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

38:3  error  Assigned variable perPage needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/dom/src/dom.js

395:4  error  Assigned variable selection needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

399:3  error  Assigned variable selection needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/edit-post/src/hooks/validate-multiple-use/index.js

42:4  error  Assigned variable blocks needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/components/block-drop-zone/index.js

101:4  error  Assigned variable srcRootClientId needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

101:4  error  Assigned variable srcIndex needlessly assigned         rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/components/block-switcher/index.js

61:5  error  Assigned variable blockType needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/components/post-saved-state/index.js

69:4  error  Assigned variable hasPublishAction needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

78:4  error  Assigned variable hasPublishAction needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

82:4  error  Assigned variable hasPublishAction needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

86:4  error  Assigned variable hasPublishAction needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/components/rich-text/index.js

246:5  error  Assigned variable item needlessly assigned    rule-no-unused-vars-before-return/no-unused-vars-before-return

621:4  error  Assigned variable record needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/editor-styles/ast/parse.js

179:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

189:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

236:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

242:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

304:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

323:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

330:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

335:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

347:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

367:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

372:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

372:4  error  Assigned variable supports needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

378:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

378:4  error  Assigned variable supports needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

378:4  error  Assigned variable style needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

397:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

401:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

407:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

407:4  error  Assigned variable style needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

425:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

430:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

430:4  error  Assigned variable media needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

436:4  error  Assigned variable media needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

436:4  error  Assigned variable style needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

436:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

454:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

472:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

478:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

491:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

509:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

516:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

516:4  error  Assigned variable vendor needlessly assigned    rule-no-unused-vars-before-return/no-unused-vars-before-return

516:4  error  Assigned variable doc needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

522:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

522:4  error  Assigned variable vendor needlessly assigned    rule-no-unused-vars-before-return/no-unused-vars-before-return

522:4  error  Assigned variable doc needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

522:4  error  Assigned variable style needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

541:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

545:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

558:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

595:5  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return

634:4  error  Assigned variable pos needlessly assigned       rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/editor-styles/ast/stringify/identity.js

250:3  error  Assigned variable indent needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/store/effects.js

167:4  error  Assigned variable blockB needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/store/effects/posts.js

58:3  error  Assigned variable post needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return
/Users/andrew/Documents/Code/vvv/www/editor/htdocs/wp-content/plugins/gutenberg/packages/editor/src/store/selectors.js

298:4  error  Assigned variable edits needlessly assigned     rule-no-unused-vars-before-return/no-unused-vars-before-return

355:3  error  Assigned variable password needlessly assigned  rule-no-unused-vars-before-return/no-unused-vars-before-return

[jorgefilipecosta]

Nice exploration 👍

We often destructure-assign a variable which may not be used before the return (example)
Solution Exempt destructuring?

For the destructuring case, I guess an error should be thrown if none of the variables destructured is used before the return if at least one is used I think it is fine.

Solution: Limit to expensive operations; namely when initialized to CallExpression (a function call)?

Yes, I think only limiting to function calls makes sense.