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remcohaszing opened this issue Nov 5, 2020 · 10 comments · Fixed by #5728
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Rule proposal: disallow duplicate union and intersection types #2738

remcohaszing opened this issue Nov 5, 2020 · 10 comments · Fixed by #5728
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accepting prs Go ahead, send a pull request that resolves this issue enhancement: new plugin rule New rule request for eslint-plugin package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin

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@remcohaszing
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I would like to propose a new rule: no-duplicate-union-intersection.

This rule reports duplicates in unions and intersections. The autofixer will remove all duplicates, keeping the first one.

The following lines will be reported:

type A = 1 | 2 | 3 | 1;
type B = 'foo' | 'bar' | 'foo';
type C = A | B | A | B;

This will be autofixed to:

type A = 1 | 2 | 3;
type B = 'foo' | 'bar';
type C = A | B;

The rule won’t try to resolve references. This may be an addition for later.

If this is accepted, I’m willing to implement this.
@remcohaszing remcohaszing added package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin triage Waiting for team members to take a look labels Nov 5, 2020
@bradzacher
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I've thought about doing this in the past!
Definitely would be a good rule to have

@bradzacher bradzacher added enhancement: new plugin rule New rule request for eslint-plugin and removed triage Waiting for team members to take a look labels Nov 6, 2020
@kenkozheng
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Sonarqube has this rule Union and intersection types should not be defined with duplicated elements.
And I think it's a good rule to have in eslint.

Hope to get it soon.

@michaelenglo
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What is the status of this issue? I'm interested to contribute, perhaps by trying to implement this rule.

@bradzacher
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Everything in this project is community maintained! This issue has been open for 2 months and nobody's mentioned they're working on it - so it's safe to assume nobody is.

Happy to accept a PR!

@remcohaszing remcohaszing mentioned this issue Jan 5, 2021
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@remcohaszing
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I started an implementation, but lost interest at some point. The basics are pretty simple, but I can into more and more corner cases. I.e. type literals need to be compared, call signatures need to be compared, nested unions and intersections should be handled.

I might pick it up at some point, but I won’t complain if someone else wants to fix this issue. :)

@michaelenglo
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Cool! I'll see if I can send something EOW. :)

@remcohaszing
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I noticed the sort-type-union-intersection-members rule was added. It might me more worthwile to drop my merge request and reuse some logic of that rule, since basically the difference between the two is that sort-type-union-intersection-members should change the order based on the the comparator result, and no-duplicate-union-intersection should remove one entry if the comparator returns 0.

@geraintwhite geraintwhite mentioned this issue Sep 17, 2021
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@JoshuaKGoldberg JoshuaKGoldberg added the accepting prs Go ahead, send a pull request that resolves this issue label Oct 25, 2021
@JoshuaKGoldberg JoshuaKGoldberg mentioned this issue Dec 18, 2021
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@bradzacher bradzacher changed the title new rule: no-duplicate-union-intersection Rule proposal: disallow duplicate union and intersection types May 3, 2022
@dashed dashed mentioned this issue Jun 2, 2022
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@sajikix
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sajikix commented Sep 27, 2022

What is the status of this issue? (Is anyone working on this issue?)
I would like to implement this rule if no one is working on this issue.

@bradzacher
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Currently open for anyone to work on - just needs a champion to implement it!

@sajikix sajikix mentioned this issue Oct 3, 2022
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@EvgenyOrekhov
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This is available in eslint-plugin-sonar (no-duplicate-in-composite rule)

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accepting prs Go ahead, send a pull request that resolves this issue enhancement: new plugin rule New rule request for eslint-plugin package: eslint-plugin Issues related to @typescript-eslint/eslint-plugin
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feat(eslint-plugin): add no-duplicate-type-constituents rule sajikix/typescript-eslint
7 participants
@remcohaszing @JoshuaKGoldberg @kenkozheng @bradzacher @EvgenyOrekhov @sajikix @michaelenglo