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README.md

logcheck tool

Description

This directory contains a tool for checking structured logging calls to logr.Logger instances (inspired by klog's logcheck). It checks Info, Error and WithValues calls for common programmer-level errors. For example, it verifies that

  • calls are made with key-value pairs (even number of variadic args)
  • messages don't contain printf format specifiers (%s and friends)

Furthermore, it verifies compliance with several aspects of our logging guideline (e.g., constant messages and keys, capitalized messages, etc.).

Motivation

The tool was created to support the migration from unstructured logging with logrus to structured logging with logr in the context of gardener/gardener#4251. With this tool we will be able to prevent bugs caused by switching to a new logging style (e.g. panic due to odd number of args). Also, it helps to make logging in our components more consistent across the entire codebase despite the high number of contributors.

Implementation Details

The tool is implemented using the golang.org/x/tools/go/analysis package, which is a "linter framework" used by go vet and golangci-lint as well. If you are looking for a better understanding of how the tool is implemented, you can take a look at this tutorial on writing custom linters, which explains all the fundamental building blocks.

Installation und Usage

There are two options for installing and using the logcheck tool:

  • standalone binary: simple, but limited
  • golangci-lint plugin (recommended): specific build requirements, but comes with caching, nice output, and flexible configuration options (e.g., excludes and //nolint comments) out of the box

Standalone Binary

Install the tool with:

go install github.com/gardener/gardener/hack/tools/logcheck

Use it with:

logcheck package [package...]

golangci-lint Plugin (Recommended)

golangci-lint features a mechanism for loading custom linters using Go's plugin library.

Build the plugin with:

CGO_ENABLED=1 go build -o logcheck.so -buildmode=plugin github.com/gardener/gardener/hack/tools/logcheck/plugin

⚠️ Both the golangci-lint binary and the logcheck plugin have to be built with CGO_ENABLED=1 for the plugin mechanism to work. See golangci/golangci-lint#1276 for more details. This means, you can't use released binaries from GitHub or Homebrew for example, but have to build the binary yourself.

Load the plugin by adding the following to your .golangci.yaml configuration file:

linters-settings:
  custom:
    logcheck:
      path: hack/tools/bin/logcheck.so
      description: Check structured logging calls to logr.Logger instances
      original-url: github.com/gardener/gardener/hack/tools/logcheck

ℹ️ In order for the plugin mechanism to work, all versions of plugin dependencies that overlap with golangci-lint must be set to the same version. You can see the versions by running go version -m golangci-lint.

Now, logcheck is executed along with all other linters:

golangci-lint run ./...

This repository is configured to run logcheck as a golangci-lint plugin along with all other linters on:

make check