gocritic: add support for variable substitution in ruleguard path settings

[sebastien-rosset]

It makes it possible to use variable substitution in the .golangci.yaml file for the gocritic ruleguard checker:

ruleguard:
        # path to a gorules file for the ruleguard checker
        rules: '${configDir}/rules/*.go'

In the above configuration, ${configDir} is substituted by the directory where the .golangci.yaml config file was found.

For example, suppose the config file is at /users/bob/.golangci.yaml and the ruleguard files are at /users/bob/ruleguard/*.go. Then previously the gocritic settings had to be configured with something like this:

# The gocritic linter has a `ruleguard` checker 
ruleguard:
  # comma-separated list of glob paths to gorules files for the ruleguard checker
  rules: '/users/bob/ruleguard/*.go'

If the ruleguard paths are relative, they are relative to the working directory where the golangci-lint command runs, not the directory where the .golangci.yaml exists.

Details:

1. Add new GetConfigDir() function in pkg/config/config.go
2. In the gocritic settings, perform variable substitution before passing the parameters to the gocritic checkers. Specifically, resolve ${configDir} to the value of Config.GetConfigDir()
3. Add code comments to document existing functions.
4. Fix .golangci.example.yml to remove warnings that can easily be prevented. Using the file as is was causing the following issues. The file (intentionally?) causes validation issues as is, but still it makes sense to reduce the number of issues.

golangci-lint run -c .golangci.example.yml 
ERRO Unable to load custom analyzer example:/path/to/example.so, plugin: not implemented 
WARN No need to enable check "rangeValCopy": it's already enabled 
WARN Gocritic settings were provided for not enabled check "unnamedresult" 
WARN Gocritic settings were provided for not enabled check "nestingreduce" 
WARN Gocritic settings were provided for not enabled check "truncatecmp" 
WARN Gocritic settings were provided for not enabled check "ruleguard" 
ERRO Running error: --presets is incompatible with --enable-all 

If this PR is accepted, then I will add more details to the documentation in #2304.

Fixes #1662
Fixes go-critic/go-critic#1143

[sebastien-rosset]

• @quasilyte since he is the author of gocritic and ruleguard.

[quasilyte]

Does this PR resolve #1662?

[sebastien-rosset]

Does this PR resolve #1662?

Yes

[quasilyte]

LGTM, but someone from the maintainers needs to review it anyway. :)

[SVilgelm]

LGTM, but it definitely needs some tests. Please add at least the functional tests

[sebastien-rosset]

LGTM, but it definitely needs some tests. Please add at least the functional tests

Good point. There didn't seem to be any functional test for ruleguard rules.

1. Add ruleguard check in test/testdata/configs/gocritic.yml.
2. Use ${configDir} variable substitution in rules parameter.
3. Add two ruleguard rules in test/testdata/configs/ruleguard/*.go.
4. Add debug, failOn and rules parameters in the test gocritic functional test.
5. Update test/testdata/gocritic.go to include static analysis issues for ruleguard.

[SVilgelm]

LGTM

[ldez]

There is something that I don't understand: I added myself as a reviewer, some people approved without waiting, after that I added myself as assignee, and the PR is merged.
I'm not sure if it's the right workflow...

[SVilgelm]

sorry, didn't pay attention

[SVilgelm]

we can revert if anything is wrong here