@nrwl/linter: add support/option to builder to run lint only on touched files in affected tree

Description + Motivation

Currently when affected is executed it runs all targets on whole affected tree, which makes 100% sense for:

• build
• test
• e2e
• type-check ( not part of standard targets but we’re using it at work to run tsc)

those afformentioned targets are real safe-guards in terms of not breaking API/application

Now for lint on the other hand, we know it’s not necessary ( for our monorepo project 5k + modules ).

What we can say with confidence, is, that for our use case, it would make sense, to run linter only on touched files per project in particular affected tree, thus rapidly speeding up linting process on CI.

NOTE: you might be thinking, there is this cache option, provided by native eslint —> well in short, that doesn’t work properly, especially on CI

Edge cases:

let’s say we have this simple dep graph

// lib A uses lib B
[ lib A ]  ---> [ lib B ]

• if one uses type aware lint rules from @typescript-eslint/no-unsafe- family and they are set to severity: error, and owner of libB changes api to return any ( which is a type information breaking change, which could be possibly catched by TypeScript anyways ), then consumer of libB (libA) would contain invalid code from linter perspective, thus introduce error to other developers after it was merged

Suggested Implementation

I’d add new option flag to current builder, to support this behaviour as an opt-in feature, which would not introduce breaking changes.

"lint": {
          "builder": "@nrwl/linter:lint",
          "options": {
            "linter": "eslint",
            "config": "path/to/lib/.eslintrc",
            "tsConfig": [
               "path/to/lib/tsconfig.lib.json",
              "path/to/lib/tsconfig.spec.json"
            ],
            "exclude": ["**/node_modules/**"],
+           "touchedOnly": true
          }
        }

with that touchedOnly could just extract touched files internaly and provide those to already supported --files flag

Alternate Implementations

[Hotell]

@cafesanu I’ll soon release lint builder with this functionality 😃

[Hotell]

Nice! is this part of the new eslint builder in 10.3.0?

Nope, my implementation covering this proposal - we use it at work already 😃