add @backstage/eslint-plugin

[Rugvip]

Hey, I just made a Pull Request!

Broke this out of #15816 as it was getting a bit out of hand.

This now adds 3 new rules:

Rule	Description
@backstage/no-forbidden-package-imports	Disallow internal monorepo imports from package subpaths that are not exported.
@backstage/no-relative-monorepo-imports	Forbid relative imports that reach outside of the package in a monorepo.
@backstage/no-undeclared-imports	Forbid imports of external packages that have not been declared in the appropriate dependencies field in package.json.

All in all it adds support for the "exports" field in package.json, bakes in the relative ../*/src check, and replaces the monorepo plugin with our own that works regardless of cwd, fixing #16074.

Custom rules also let us provide more accurate error messages, for example:

lodash must be declared in dependencies of packages/app/package.json, run 'yarn --cwd packages/app add lodash' from the project root.

The replacement of the import/no-extraneous-dependencies rule also comes with a decent speed boost, as it was by far the slowest rule.

before:

yarn lint:all  101.85s user 9.80s system 639% cpu 17.463 total
yarn lint:all  101.67s user 9.93s system 638% cpu 17.491 total
yarn lint:all  100.20s user 9.98s system 644% cpu 17.089 total

Rule                              | Time (ms) | Relative
:---------------------------------|----------:|--------:
import/no-extraneous-dependencies |  1320.333 |    21.0%
@typescript-eslint/no-redeclare   |   798.291 |    12.7%
monorepo/no-relative-import       |   458.716 |     7.3%
notice/notice                     |   318.667 |     5.1%
react/no-multi-comp               |   184.161 |     2.9%
jest/expect-expect                |   181.801 |     2.9%
monorepo/no-internal-import       |   159.004 |     2.5%
react/sort-comp                   |   126.132 |     2.0%
jest/no-standalone-expect         |   118.181 |     1.9%
jest/no-conditional-expect        |   115.060 |     1.8%

after:

yarn lint:all  98.91s user 7.84s system 622% cpu 17.152 total
yarn lint:all  92.07s user 8.19s system 617% cpu 16.229 total
yarn lint:all  97.77s user 7.90s system 634% cpu 16.664 total

Rule                                    | Time (ms) | Relative
:---------------------------------------|----------:|--------:
@typescript-eslint/no-redeclare         |   981.920 |    17.7%
notice/notice                           |   458.716 |     8.3%
@backstage/no-undeclared-imports        |   273.522 |     4.9%
@backstage/no-relative-monorepo-imports |   264.021 |     4.8%
jest/expect-expect                      |   230.718 |     4.2%
react/no-multi-comp                     |   190.179 |     3.4%
jest/no-standalone-expect               |   134.748 |     2.4%
no-restricted-globals                   |   133.390 |     2.4%
jest/no-conditional-expect              |   115.549 |     2.1%
react/sort-comp                         |   113.047 |     2.0%

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)
• All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie]

Missing Changesets

The following package(s) are changed by this PR but do not have a changeset:

• @backstage/backend-defaults
• @backstage/core-plugin-api
• @techdocs/cli
• @backstage/plugin-catalog-backend-module-incremental-ingestion
• @backstage/plugin-cost-insights
• @backstage/plugin-scaffolder-backend
• @backstage/plugin-splunk-on-call

See CONTRIBUTING.md for more information about how to add changesets.

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
example-app	packages/app	none	v0.2.80-next.1
@backstage/backend-defaults	packages/backend-defaults	none	v0.1.7-next.1
@backstage/backend-test-utils	packages/backend-test-utils	patch	v0.1.34-next.1
@backstage/cli	packages/cli	patch	v0.22.2-next.0
@backstage/codemods	packages/codemods	patch	v0.1.42
@backstage/core-plugin-api	packages/core-plugin-api	none	v1.3.0
@backstage/create-app	packages/create-app	patch	v0.4.37-next.1
e2e-test	packages/e2e-test	none	v0.2.0
@backstage/eslint-plugin	packages/eslint-plugin	minor	v0.0.0
@backstage/repo-tools	packages/repo-tools	patch	v0.1.1
techdocs-cli-embedded-app	packages/techdocs-cli-embedded-app	none	v0.2.79-next.1
@techdocs/cli	packages/techdocs-cli	none	v1.3.2-next.1
@backstage/plugin-catalog-backend-module-incremental-ingestion	plugins/catalog-backend-module-incremental-ingestion	none	v0.2.0-next.1
@backstage/plugin-cost-insights	plugins/cost-insights	none	v0.12.4-next.1
@backstage/plugin-scaffolder-backend	plugins/scaffolder-backend	none	v1.11.0-next.1
@backstage/plugin-splunk-on-call	plugins/splunk-on-call	none	v0.4.4-next.1

[github-actions]

Uffizzi Preview deployment-13522 was deleted.

[github-actions]

Thank you for contributing to Backstage! The changes in this pull request will be part of the 1.11.0 release, scheduled for Tue, 14 Feb 2023.

[torsami77]

Hi @Rugvip, job well done, I'm having issue with Disallow internal monorepo imports from package subpaths that are not exported. since this update despite exporting package from internal monorepo. Please can you provide a code snippet example or reference, I keep getting @internal/plugin-core-react does not export ....

[Rugvip]

@torsami77 thanks! Could you show an example where you get that error? The rule is there to forbid importing of subpaths like @internal/my-plugin/components where /components is the subpath that will only be allowed if it's listed in the package.json exports field.

[torsami77]

Thanks for your quick response @Rugvip, I need an example on how to properly config the export in package.json

[Rugvip]

@torsami77 that's all over here https://backstage.io/docs/local-dev/cli-build-system#subpath-exports

[torsami77]

okay thanks, let me take a look

[torsami77]

@Rugvip , thank you for your help, the reference you provided above helped me resolve the lint error, but now I'm trying to run the app and I'm getting similar issues as on #13982