Reorganise the magefile

.ci/Jenkinsfile

@@ -37,7 +37,7 @@ pipeline {
         withGithubNotify(context: "Lint") {
           dir("${BASE_DIR}"){
             withMageEnv(){
-              sh(label: 'Mage check', script: 'mage check')
+              sh(label: 'Mage check', script: 'mage -v check')
             }
           }
         }

.golangci.yml

@@ -3,6 +3,16 @@ run:
   # timeout for analysis, e.g. 30s, 5m, default is 1m
   timeout: 1m
 
+issues:
+  # Maximum count of issues with the same text.
+  # Set to 0 to disable.
+  # Default: 3
+  max-same-issues: 0
+  # Maximum issues count per one linter.
+  # Set to 0 to disable.
+  # Default: 50
+  max-issues-per-linter: 0
+
 output:
   sort-results: true
 

magefile.go

@@ -36,81 +36,137 @@ import (
 )
 
 const (
-	linterInstallFilename = "./intall-golang-ci.sh"
-	linterBinaryFilename  = "./bin/golangci-lint"
+	linterInstallURL      = "https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh"
+	linterInstallFilename = "./build/intall-golang-ci.sh"
+	linterBinaryFilename  = "./build/golangci-lint"
 	linterVersion         = "v1.44.0"
 )
 
-// InstallLinter installs golangci-lint (https://golangci-lint.run) to `./bin`
+// Aliases are shortcuts to long target names.
+// nolint: deadcode // it's used by `mage`.
+var Aliases = map[string]interface{}{
+	"llc":  Linter.LastChange,
+	"lint": Linter.All,
+}
+
+// Linter contains targets related to linting the Go code
+type Linter mg.Namespace
+
+// Install installs golangci-lint (https://golangci-lint.run) to `./build`
 // using the official installation script downloaded from GitHub.
 // If the linter binary already exists does nothing.
-func InstallLinter() error {
-	_, err := os.Stat(linterBinaryFilename)
+func (Linter) Install() error {
+	dirPath := filepath.Dir(linterBinaryFilename)
+	err := os.MkdirAll(dirPath, 0700)
+	if err != nil {
+		return fmt.Errorf("failed to create path %q: %w", dirPath, err)
+	}
+
+	_, err = os.Stat(linterBinaryFilename)
 	if err == nil {
-		log.Println("already installed, exiting...")
+		log.Println("the linter has been already installed, skipping...")
 		return nil
 	}
 	if !errors.Is(err, os.ErrNotExist) {
-		return err
+		return fmt.Errorf("failed check if file %q exists: %w", linterBinaryFilename, err)
 	}
 
 	log.Println("preparing the installation script file...")
+
 	installScript, err := os.OpenFile(linterInstallFilename, os.O_TRUNC|os.O_CREATE|os.O_WRONLY, 0700)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to create file %q: %w", linterInstallFilename, err)
 	}
 	defer installScript.Close()
 
 	log.Println("downloading the linter installation script...")
-	resp, err := http.Get("https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh")
+	// nolint: noctx // valid use since there is no context
+	resp, err := http.Get(linterInstallURL)
 	if err != nil {
-		return err
+		return fmt.Errorf("cannot download the linter installation script from %q: %w", linterInstallURL, err)
 	}
 	defer resp.Body.Close()
 
-	lr := io.LimitReader(resp.Body, 1024*100) // not more than 100 KB
+	lr := io.LimitReader(resp.Body, 1024*100) // not more than 100 KB, just to be safe
 	_, err = io.Copy(installScript, lr)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to finish downloading the linter installation script: %w", err)
 	}
 
 	err = installScript.Close() // otherwise we cannot run the script
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to close file %q: %w", linterInstallFilename, err)
+	}
+
+	binaryDir := filepath.Dir(linterBinaryFilename)
+	err = os.MkdirAll(binaryDir, 0700)
+	if err != nil {
+		return fmt.Errorf("cannot create path %q: %w", binaryDir, err)
 	}
 
-	return sh.Run(linterInstallFilename, linterVersion)
+	// there must be no space after `-b`, otherwise the script does not work correctly ¯\_(ツ)_/¯
+	return sh.Run(linterInstallFilename, "-b"+binaryDir, linterVersion)
 }
 
-// LintAll runs the linter against the entire codebase
-func LintAll() error {
-	mg.Deps(InstallLinter)
-	return sh.Run(linterBinaryFilename, "-v", "run", "./...")
+// All runs the linter against the entire codebase
+func (l Linter) All() error {
+	mg.Deps(l.Install)
+	return runLinter()
 }
 
+// LastChange runs the linter against all files changed since the fork point from `main`.
+// If the current branch is `main` then runs against the files changed in the last commit.
+func (l Linter) LastChange() error {
+	mg.Deps(l.Install)
+
+	branch, err := sh.Output("git", "branch", "--show-current")
+	if err != nil {
+		return fmt.Errorf("failed to get the current branch: %w", err)
+	}
+
+	// the linter is supposed to support linting changed diffs only but,
+	// for some reason, it simply does not work - does not output any
+	// results without linting the whole files, so we have to use `--whole-files`
+	// which can lead to some frustration from developers who would like to
+	// fix a single line in an existing codebase and the linter would force them
+	// into fixing all linting issues in the whole file instead
+
+	if branch == "main" {
+		// files changed in the last commit
+		return runLinter("--new-from-rev=HEAD~", "--whole-files")
+	}
+
+	return runLinter("--new-from-rev=origin/main", "--whole-files")
+}
+
+// Check runs all the checks
+// nolint: deadcode,unparam // it's used as a `mage` target and requires returning an error
 func Check() error {
-	mg.Deps(CheckNoBeatsDependency, CheckModuleTidy, LintAll)
+	mg.Deps(Deps.CheckNoBeats, Deps.CheckModuleTidy, Linter.LastChange)
 	return nil
 }
 
-// CheckNoBeatsDependency is required to make sure we are not introducing
+// Deps contains targets related to checking dependencies
+type Deps mg.Namespace
+
+// CheckNoBeats is required to make sure we are not introducing
 // dependency on elastic/beats.
-func CheckNoBeatsDependency() error {
+func (Deps) CheckNoBeats() error {
 	goModPath, err := filepath.Abs("go.mod")
 	if err != nil {
 		return err
 	}
 	goModFile, err := os.Open(goModPath)
 	if err != nil {
-		return fmt.Errorf("failed to open module file: %+v", err)
+		return fmt.Errorf("failed to open module file: %w", err)
 	}
 	beatsImport := []byte("github.com/elastic/beats")
 	scanner := bufio.NewScanner(goModFile)
 	lineCount := 1
 	for scanner.Scan() {
 		line := scanner.Bytes()
 		if bytes.Contains(line, beatsImport) {
-			return fmt.Errorf("line %d is beats dependency: '%s'\nPlease, make sure you are not adding anything that depends on %s", lineCount, line, beatsImport)
+			return fmt.Errorf("line %d is a beats dependency: '%s'\nPlease, make sure you are not adding anything that depends on %s", lineCount, line, beatsImport)
 		}
 		lineCount++
 	}
@@ -120,16 +176,38 @@ func CheckNoBeatsDependency() error {
 	return nil
 }
 
-// CheckModuleTidy checks if `go mod tidy` was run before.
-func CheckModuleTidy() error {
+// CheckModuleTidy checks if `go mod tidy` was run before the last commit.
+func (Deps) CheckModuleTidy() error {
 	err := sh.Run("go", "mod", "tidy")
 	if err != nil {
 		return err
 	}
-	err = sh.Run("git", "diff", "--exit-code")
+	err = sh.Run("git", "diff", "--exit-code", "go.mod")
 	if err != nil {
-		return fmt.Errorf("`go mod tidy` was not called before committing: %w", err)
+		return fmt.Errorf("`go mod tidy` was not called before the last commit: %w", err)
 	}
 
 	return nil
 }
+
+// runWithStdErr runs a command redirecting its stderr to the console instead of discarding it
+func runWithStdErr(command string, args ...string) error {
+	_, err := sh.Exec(nil, os.Stdout, os.Stderr, command, args...)
+	return err
+}
+
+// runLinter runs the linter passing the `mage -v` (verbose mode) and given arguments.
+// Also redirects linter's output to the `stderr` instead of discarding it.
+func runLinter(runFlags ...string) error {
+	var args []string
+
+	if mg.Verbose() {
+		args = append(args, "-v")
+	}
+
+	args = append(args, "run")
+	args = append(args, runFlags...)
+	args = append(args, "./...")
+
+	return runWithStdErr(linterBinaryFilename, args...)
+}