feat: add zero linter

[leonklingele]

The zero linter finds unnecessary zero-value assignments when short-hand declaring & initializing a variable:

package a

var _ string = "" // want "shoud not assign zero value"

func _() {
	n := 0 // want "shoud not assign zero value"
	_ = n

	var _ []int = nil     // want "shoud not assign zero value"
	var _ []int = []int{} // OK
	m := int32(0)         // OK
	_ = m
	var _ *int = nil            // want "shoud not assign zero value"
	var _ struct{} = struct{}{} // want "shoud not assign zero value"
	var _, _ int                // OK
	var _, _ int = 0, 1         // want "shoud not assign zero value"
	var _, _ int = 1, 2         // OK
	var _, _ int = 1 - 1, 2 - 2 // want "shoud not assign zero value" "shoud not assign zero value"
	var _ bool = false          // want "shoud not assign zero value"
	var _ bool = true           // OK

	type T struct{ N int }
	var _ T = T{} // want "shoud not assign zero value"
}

https://github.com/gostaticanalysis/zero

Fixes #3491

[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.

[alexandear]

please fix the typo in should

[Antonboom]

1. Naming proposal – nozeroassign. zero is too general, is not it?
2. Maybe better to make it part of ineffassign?
3. Does it cover How to check 'Declaring Empty Slices' #3248?