Add mage notice target (elastic#3772)

* Add mage notice target

* Make linter happy

Makefile

@@ -29,17 +29,7 @@ help: Makefile
 ## notice : Generates the NOTICE file.
 .PHONY: notice
 notice:
-	@echo "Generating NOTICE"
-	go mod tidy
-	go mod download
-	go list -m -json all | go run go.elastic.co/go-licence-detector \
-		-includeIndirect \
-		-rules dev-tools/notice/rules.json \
-		-overrides dev-tools/notice/overrides.json \
-		-noticeTemplate dev-tools/notice/NOTICE.txt.tmpl \
-		-noticeOut NOTICE.txt \
-		-depsOut ""
-	cat dev-tools/notice/NOTICE.txt.append >> NOTICE.txt
+	@mage notice
 
 ## check-ci: Run all the checks under the ci, this doesn't include the linter which is run via a github action.
 .PHONY: check-ci

dev-tools/mage/target/common/notice.go

@@ -0,0 +1,119 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+package common
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/magefile/mage/sh"
+)
+
+func runCommand(cmd string, args ...string) error {
+	s := strings.Join(append([]string{cmd}, args...), " ")
+	fmt.Printf(">> %s\n", s)
+	err := sh.Run(cmd, args...)
+	if err != nil {
+		return fmt.Errorf("failed running %s, please fix the issues reported: %w", s, err)
+	}
+	return nil
+}
+
+// Notice Generates NOTICE.txt.
+func Notice() (err error) {
+	fmt.Println("Generating NOTICE")
+	if err := runCommand("go", "mod", "tidy"); err != nil {
+		return err
+	}
+	if err := runCommand("go", "mod", "download"); err != nil {
+		return err
+	}
+
+	// piping output of the first command to the second
+	// similar to former Makefile implementation
+	//
+	// go list -m -json all | go run go.elastic.co/go-licence-detector \
+	// -includeIndirect \
+	// -rules dev-tools/notice/rules.json \
+	// -overrides dev-tools/notice/overrides.json \
+	// -noticeTemplate dev-tools/notice/NOTICE.txt.tmpl \
+	// -noticeOut NOTICE.txt \
+	// -depsOut ""
+	listCmd := exec.Command("go", "list", "-m", "-json", "all")
+	licDetectCmd := exec.Command("go", "run", "go.elastic.co/go-licence-detector",
+		"-includeIndirect",
+		"-rules", "dev-tools/notice/rules.json",
+		"-overrides", "dev-tools/notice/overrides.json",
+		"-noticeTemplate", "dev-tools/notice/NOTICE.txt.tmpl",
+		"-noticeOut", "NOTICE.txt",
+		"-depsOut", "")
+
+	fmt.Printf(">> %s | %s\n", strings.Join(listCmd.Args, " "), strings.Join(licDetectCmd.Args, " "))
+
+	r, w := io.Pipe()
+	defer r.Close()
+	defer w.Close()
+
+	var buf bytes.Buffer
+	listCmd.Stdout = w
+	licDetectCmd.Stdin = r
+	licDetectCmd.Stderr = &buf
+
+	if err := listCmd.Start(); err != nil {
+		return err
+	}
+	if err := licDetectCmd.Start(); err != nil {
+		return err
+	}
+
+	if err := listCmd.Wait(); err != nil {
+		return err
+	}
+	w.Close()
+
+	if err := licDetectCmd.Wait(); err != nil {
+		// copy error to stdout, helpful if tool failed
+		if _, cerr := io.Copy(os.Stdout, &buf); cerr != nil {
+			return errors.Join(fmt.Errorf("failed to read stderr: %w", cerr), err)
+		}
+		return err
+	}
+
+	// cat dev-tools/notice/NOTICE.txt.append >> NOTICE.txt
+	fmt.Printf(">> %s\n", "cat dev-tools/notice/NOTICE.txt.append >> NOTICE.txt")
+	const (
+		infn  = "dev-tools/notice/NOTICE.txt.append"
+		outfn = "NOTICE.txt"
+	)
+
+	f, err := os.Open(infn)
+	if err != nil {
+		return fmt.Errorf("failed to open file %s: %w", infn, err)
+	}
+	defer f.Close()
+
+	out, err := os.OpenFile(outfn, os.O_WRONLY|os.O_APPEND, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open file %s: %w", outfn, err)
+	}
+
+	defer func() {
+		cerr := out.Close()
+		if err == nil {
+			err = cerr
+		}
+	}()
+
+	if _, err := io.Copy(out, f); err != nil {
+		return fmt.Errorf("failed to append file %s: %w", outfn, err)
+	}
+
+	return nil
+}