add eslint

[with-heart]

This PR installs and configures eslint with typescript-eslint.

It uses the new flat config format (which is such a nice improvement imo), along with the recommended rules from @eslint/js and typescript-eslint.

Since #5022 is a thing, I added all test.* files to the global ignores. Once that lands we can remove this and maybe add eslint-plugin-vitest.

[changeset-bot[bot]]

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Latest commit: aee03ce72e0a9d854ee357d581da833a8f70c726

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[with-heart]

I wanted to try this with type-aware linting but it reported hundreds of errors that didn't seem like they'd be easy to fix. They're likely related to having to set @typescript-eslint/no-explicit-any to warn (581 warnings for that rule alone 😬).

[Andarist]

how many we'd get after disabling @typescript-eslint/no-explicit-any?

[with-heart]

@Andarist 0. Should we disable it? I wasn't sure if this was something that'd be worth trying to deal with or not

[with-heart]

I'm not sure what the deal is with the failed check. The error it reports isn't actually relevant.

Here's the actual error:

This syntax is reserved in files with the .mts or .cts extension. Add a trailing comma, as in `<T,>() => ...`. (20:14)

To make build work, I have to add a trailing comma to type params in packages/xstate-solid:

diff --git a/packages/xstate-solid/src/createImmutable.ts b/packages/xstate-solid/src/createImmutable.ts
index 5624473d5b..e3237c7414 100644
--- a/packages/xstate-solid/src/createImmutable.ts
+++ b/packages/xstate-solid/src/createImmutable.ts
@@ -19,7 +19,7 @@ const updateStore = <Path extends unknown[]>(
   store: Store<any>
 ) => {
   const valueRefs = new WeakMap<any, unknown>();
-  const diff = <CompareValue>(
+  const diff = <CompareValue,>(
     next: CompareValue,
     prev: CompareValue,
     path: Path
diff --git a/packages/xstate-solid/src/deepClone.ts b/packages/xstate-solid/src/deepClone.ts
index e829300845..58bc92e28d 100644
--- a/packages/xstate-solid/src/deepClone.ts
+++ b/packages/xstate-solid/src/deepClone.ts
@@ -17,7 +17,7 @@ export function isWrappable(obj: any): obj is object {
  * @param valueRefs A WeakMap that stores a reference from the original
  *   object/array to the cloned object/array
  */
-const clone = <T>(value: T, valueRefs: WeakMap<any, any>): T => {
+const clone = <T,>(value: T, valueRefs: WeakMap<any, any>): T => {
   if (!isWrappable(value)) {
     return value;
   }
@@ -47,4 +47,4 @@ const clone = <T>(value: T, valueRefs: WeakMap<any, any>): T => {
   return clonedValue;
 };

-export const deepClone = <T>(value: T): T => clone(value, new WeakMap());
+export const deepClone = <T,>(value: T): T => clone(value, new WeakMap());

These previously used extends unknown:

diff --git a/packages/xstate-solid/src/createImmutable.ts b/packages/xstate-solid/src/createImmutable.ts
index 7764371bac..e3237c7414 100644
--- a/packages/xstate-solid/src/createImmutable.ts
+++ b/packages/xstate-solid/src/createImmutable.ts
@@ -19,7 +19,7 @@ const updateStore = <Path extends unknown[]>(
   store: Store<any>
 ) => {
   const valueRefs = new WeakMap<any, unknown>();
-  const diff = <CompareValue extends unknown>(
+  const diff = <CompareValue,>(
     next: CompareValue,
     prev: CompareValue,
     path: Path
diff --git a/packages/xstate-solid/src/deepClone.ts b/packages/xstate-solid/src/deepClone.ts
index 1eeaa76a2d..58bc92e28d 100644
--- a/packages/xstate-solid/src/deepClone.ts
+++ b/packages/xstate-solid/src/deepClone.ts
@@ -17,10 +17,7 @@ export function isWrappable(obj: any): obj is object {
  * @param valueRefs A WeakMap that stores a reference from the original
  *   object/array to the cloned object/array
  */
-const clone = <T extends unknown>(
-  value: T,
-  valueRefs: WeakMap<any, any>
-): T => {
+const clone = <T,>(value: T, valueRefs: WeakMap<any, any>): T => {
   if (!isWrappable(value)) {
     return value;
   }
@@ -50,5 +47,4 @@ const clone = <T extends unknown>(
   return clonedValue;
 };

-export const deepClone = <T extends unknown>(value: T): T =>
-  clone(value, new WeakMap());
+export const deepClone = <T,>(value: T): T => clone(value, new WeakMap());

Not really sure what the issue is here and prettier removes the dangling commas so it's not really a fix.

[boneskull]

I wanted to try this with type-aware linting but it reported hundreds of errors that didn't seem like they'd be easy to fix. They're likely related to having to set @typescript-eslint/no-explicit-any to warn (581 warnings for that rule alone 😬).

IMO this is worth doing. You will probably need to disable stuff if using the recommendedTypeChecked preview; it's pretty strict.

Here's some of the rules I'd suggest tweaking:

// and sometimes you gotta use any
'@typescript-eslint/no-explicit-any': 'off',

// allow ! 
'@typescript-eslint/no-non-null-assertion': 'off',

// allow prefixing unused vars with _
'@typescript-eslint/no-unused-vars': [
  'error',
  {
    argsIgnorePattern: '^_',
    varsIgnorePattern: '^_',
  },
],

// better for overloads
'@typescript-eslint/unified-signatures': [
  'error',
  {
    ignoreDifferentlyNamedParameters: true,
  },
],

Something like the above might get you out of the woods.

Also I'd recommend enabling this (if it's not already enabled by default), which surfaces unused // eslint-disable directives:

{
  linterOptions: {
    reportUnusedDisableDirectives: 'error',
  },
}

I'm not sure what you were using for the parser config, but this is what has worked well for me with tseslint@v8.

languageOptions: {
  parserOptions: {
    projectService: {
      // type-aware linting for non-project config files. modify as necessary
      allowDefaultProject: ['*.js', '.*.js'],
    },
    tsconfigRootDir: import.meta.dirname, // (or __dirname, depending)
  },
},

[boneskull]

I don't think T extends unknown is doing anything in that function, and can just be T.

[davidkpiano]

@with-heart Can you resolve merge conflicts?

[with-heart]

@with-heart Can you resolve merge conflicts?

Done! I think we should be good to go assuming the changes look fine 🙏