feat: add untypedconst linter

[leonklingele]

The untypedconst linter ensures that untyped constant expressions are not used as values of defined (= named) types.

// The first call is valid as it is passing a typed-constant to "takesExString" which expects a typed-constant as its first parameter.
// The second call is invalid as it passes an untyped-constant which has the same underlying type as the one expected (string)
func Call() {
	takesExString(external.ExStr)
	takesExString("hoge")         // want `passing untyped constant to parameter of defined type "github.com/jiftechnify/untypedconst/pkg/external.ExString"`
[..]

https://github.com/jiftechnify/untypedconst

Fixes #3478

[ldez]

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

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(), log.fatal(), os.exit(), or similar.
• It must not have false positives/negatives. (the team will help to verify that)
• It must have tests inside golangci-lint.

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.

Recommendations

• The linter should not use SSA. (currently, SSA does not support 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.

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

[leonklingele]

Is there anything I can do to get this reviewed? Friendly ping towards @ldez :)

[leonklingele]

I really think this is a great addition to the project. I use the linter on quite a few projects already and it has proven to be super helpful. Is there anything I could do to get this merged?

[alexandear]

@leonklingele could you please resolve conflicts and update the PR according to the #3527 (comment)?

[leonklingele]

Updated, ptal.

Upstream has made some changes to comply with our requirements since: jiftechnify/untypedconst#1 (comment) 🥳

[alexandear]

@leonklingele could you address the point regarding "The Linter Tests Inside Golangci-lint: They must have at least one std lib import"?

[leonklingele]

Done 😊

EDIT: CI is failing, apparently: analysis.go:189: untypedconst.go:5:2: unexpected diagnostic: could not import fmt (Config.Importer.Import(fmt) returned nil but no error) What does that mean?