New Linter Rule - set() must return a value

[caseywatts]

having a linter rule for this would help prevent some bugs
(at least until the behavior changes to be what people expect)
emberjs/rfcs#79

Bad:

height: 100,
goldenRatioWidth: computed('height', {
  get() {
    return this.get('height') * 1.618;
  },
  set(_, value) {
    this.set('height', value / 1.618);
  }
})

Good

height: 100,
goldenRatioWidth: computed('height', {
  get() {
    return this.get('height') * 1.618;
  },
  set(_, value) {
    const newHeight = value / 1.618;
    this.set('height', newHeight);
    return newHeight;
  }
})

set() must have a return.

(I mistakenly created this over here first)

[caseywatts]

I just glanced at some of the other rules, and I'm not sure how to get started implementing this lol

@clcuevas I believe you've done some things around return statements in the past (based on my codebase spelunking) - would you have any ideas or suggestions?

[Turbo87]

@caseywatts my naive idea would be this:

In the AST look for a CallExpression node with an Identifier of computed. If the last argument is a ObjectExpression look for a Property with an Identifier of set and check if the value is a FunctionExpression. Now iterate over the body contents and check for any ReturnStatement nodes and if you can't find any you can report a lint failure.

You can use https://astexplorer.net/ to view the AST corresponding to any JS code you put in.

[clcuevas]

@caseywatts Pretty much what @Turbo87 summarized. Wish I knew of astexplorer in my previous PRs. It would have helped a lot!

Good luck!