feat(eslint-plugin): [no-duplicate-enum-values] add rule

[aifreedom]

PR Checklist

• Addresses an existing open issue: fixes disallow duplicate enum values #2693
• That issue was marked as accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

This PR creates a new rule in eslint-plugin to disallow duplicate enum values. Per discussion in the issue (#2693), in this version, it only checks enum members initialized with literals, and does not cover the ones without an initializer or initialized with an expression.

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[typescript-eslint]

Thanks for the PR, @aifreedom!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #4833 (5484161) into main (f3cf87b) will increase coverage by 2.48%.
The diff coverage is 100.00%.

❗ Current head 5484161 differs from pull request most recent head 42515fd. Consider uploading reports for the commit 42515fd to get more accurate results

@@            Coverage Diff             @@
##             main    #4833      +/-   ##
==========================================
+ Coverage   91.77%   94.25%   +2.48%     
==========================================
  Files         227      153      -74     
  Lines       10611     8305    -2306     
  Branches     3283     2703     -580     
==========================================
- Hits         9738     7828    -1910     
+ Misses        591      263     -328     
+ Partials      282      214      -68     

Flag	Coverage Δ
unittest	94.25% <100.00%> (+2.48%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/eslint-plugin/src/configs/all.ts	100.00% <ø> (ø)
...slint-plugin/src/rules/no-duplicate-enum-values.ts	100.00% <100.00%> (ø)
...ges/type-utils/src/getConstrainedTypeAtLocation.ts
...ils/src/ast-utils/eslint-utils/ReferenceTracker.ts
...s/utils/src/eslint-utils/batchedSingleLineTests.ts
packages/utils/src/ts-eslint-scope/Referencer.ts
packages/eslint-plugin-tslint/src/custom-linter.ts
packages/type-utils/src/isUnsafeAssignment.ts
...pt-estree/src/create-program/createWatchProgram.ts
packages/utils/src/ast-utils/index.ts
... and 67 more

[JoshuaKGoldberg]

The new rule and tests generally looks great, very nicely done @aifreedom!

Requesting changes for added test coverage. I can't view the Codecov coverage report at the moment to see why the file only has 80% 🙃 -- will take another look when more tests are added.

[JoshuaKGoldberg]

[Nitpicking] Is there a need to separate these two functions out? They both check that node.type === AST_NODE_TYPES.Literal.

I'd suggest either making a single separate function:

function getExpressionLiteralValue(node: TSESTree.Expression) {
  if (node.type === AST_NODE_TYPES.Literal) {
    switch (typeof node.value) {
      // ...
    }  
  }
}

...or inlining them below:

```ts
let value: string | number | undefined;

if (node.type === AST_NODE_TYPES.Literal) {
  // ...
}

Just suggestions, feel free to ignore if you don't like either of these changes 😄

[aifreedom]

I had to do this because typescript doesn't know the type of member.initializer without the util functions, and would complain when I cast its value to String or Number.

[aifreedom]

The coverage drop is a bit weird. It's an unrelated rule's coverage that dropped (no-magic-numbers). The coverage for the new rule is 100%.

[aifreedom]

I had to do this because typescript doesn't know the type of member.initializer without the util functions, and would complain when I cast its value to String or Number.

[aifreedom]

Oh, no… I updated the branch using the “rebase” button and it seemed to have forced push the commits. Sorry about the inconvenience. @JoshuaKGoldberg you can review the last two commits which have the updates addressing your comments.

[JoshuaKGoldberg]

Ha, no worries - thanks for the heads up!

And yeah I don't know what's going on with Codecov. The service has been flaky off and on the last few... years. 🙃

[JoshuaKGoldberg]

Fantastic, thanks so much @aifreedom!