feat: add sloglint linter

[tmzane]

Hello,

I'd like to add the sloglint linter.

It ensures consistent code style when using log/slog.

Currently, the following checks are available:

• Forbid mixing key-value pairs and attributes within a single function call (default)
• Enforce using either key-value pairs or attributes for the entire project (optional)
• Enforce using constants instead of raw keys (optional)
• Enforce putting arguments on separate lines (optional)

I've tested it on several big projects that use log/slog, and it works just fine 😎

[ldez]

In order for a pull request adding a linter to be reviewed, the linter and the PR must follow some requirements.

• The CLA must be signed

Pull Request Description

• It must have a link to the linter repository.
• It must provide a short description of the linter.

Linter

• It must not be a duplicate of another linter or a rule of a linter. (the team will help to verify that)
• It must have a valid license (AGPL is not allowed) and the file must contain the required information by the license, ex: author, year, etc.
• The linter repository must have a CI and tests.
• It must use go/analysis.
• It must have a valid tag, ex: v1.0.0, v0.1.0.
• It must not contain init().
• It must not contain panic().
• It must not contain log.fatal(), os.exit(), or similar.
• It must not modify the AST.
• It must not have false positives/negatives. (the team will help to verify that)
• It must have tests inside golangci-lint.
• It must work with go1.20

The Linter Tests Inside Golangci-lint

• They must have at least one std lib import.
• They must work with T=<name of the linter test file>.go make test_linters. (the team will help to verify that)

.golangci.reference.yml

• The linter must be added to the list of available linters (alphabetical case-insensitive order).
  • enable and disable options
• If the linter has a configuration, the exhaustive configuration of the linter must be added (alphabetical case-insensitive order)
  • The values must be different from the default ones.
  • The default values must be defined in a comment.
  • The option must have a short description.

Others Requirements

• The files (tests and linter) inside golangci-lint must have the same name as the linter.
• The .golangci.yml of golangci-lint itself must not be edited and the linter must not be added to this file.
• The linters must be sorted in the alphabetical order (case-insensitive) in the Manager.GetAllSupportedLinterConfigs(...) and .golangci.reference.yml.
• The load mode (WithLoadMode(...)):
  • if the linter doesn't use types: goanalysis.LoadModeSyntax
  • goanalysis.LoadModeTypesInfo required WithLoadForGoAnalysis() in the Manager.GetAllSupportedLinterConfigs(...)
• The version in WithSince(...) must be the next minor version (v1.X.0) of golangci-lint.
• WithURL() must contain the URL of the repository.

Recommendations

• The linter should not use SSA. (SSA can be a problem with generics)
• The linter repository should have a readme and linting.
• The linter should be published as a binary. (useful to diagnose bug origins)

---

The golangci-lint team will edit this comment to check the boxes before and during the review.

The code review will start after the completion of those checkboxes (except for the specific items that the team will help to verify).

If the author of the PR is a member of the golangci-lint team, he should not edit this message.

This checklist does not imply that we will accept the linter.

[ldez]

hello,

slog is a part of go1.21 but the current minimum requirement for golangci-lint is go1.20.

Another point, this linter is really close to loggercheck.

[tmzane]

Yeah, I can see that there is a problem with 1.20 in CI 🥲

We don't actually need log/slog to build the linter itself, it is imported only in tests. Maybe we can skip those for 1.20? I can also add support for x/slog to prove that it passes the tests.

Another point, this linter is really close to loggercheck.

Hmm, I thought that loggercheck only checks the odd number of keys and values? For slog this check is already covered by govet, so I don't see the point implementing it. Instead, sloglint focuses on slog-specific checks.

UPD: Now I think that x/slog support will be quite useful, since 1.20 is still officially supported. I'll add it anyway.

[ldez]

x/slog has differences with log/slog, it can be complex to support both.
You can add build tags on the test files: I implemented support for the Go version inside the test system.

[ldez]

LGTM