build: in GitHub actions output built images in job summary

Author: joonas-fi

cmd/bob/build.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -571,11 +572,26 @@ func buildEntry() *cobra.Command {
 					buildCtx.Debug = true
 				}
 
-				_, err := build(buildCtx)
+				output, err := build(buildCtx)
 				if err != nil {
 					return err
 				}
 
+				// https://github.blog/news-insights/product-news/supercharging-github-actions-with-job-summaries/
+				if stepSummaryFilename := os.Getenv("GITHUB_STEP_SUMMARY"); stepSummaryFilename != "" && len(output.images) > 0 {
+					if err := func() error {
+						stepSummaryFile, err := os.OpenFile(stepSummaryFilename, os.O_APPEND|os.O_WRONLY|os.O_CREATE, 0600)
+						if err != nil {
+							return err
+						}
+						defer stepSummaryFile.Close()
+
+						return githubStepSummaryWriteImages(stepSummaryFile, output.images)
+					}(); err != nil {
+						log.Printf("WARN: %v", err)
+					}
+				}
+
 				return nil
 			}())
 		},

cmd/bob/utils.go

@@ -6,10 +6,12 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"path"
 	"strings"
 	"sync"
 
 	"github.com/function61/turbobob/pkg/bobfile"
+	"github.com/function61/turbobob/pkg/dockertag"
 )
 
 func passthroughStdoutAndStderr(cmd *exec.Cmd) *exec.Cmd {
@@ -117,3 +119,28 @@ func firstNonEmpty(a, b string) string {
 		return b
 	}
 }
+
+// write image tags as Markdown to GitHub actions's workflow summary so it's easy from their UI to spot
+// which images were published as result of the build.
+func githubStepSummaryWriteImages(stepSummaryFile io.Writer, images []imageBuildOutput) error {
+	withErr := func(err error) error { return fmt.Errorf("githubStepSummaryWriteImages: %w", err) }
+
+	lines := []string{}
+	for _, image := range images {
+		parsed := dockertag.Parse(image.tag)
+		if parsed == nil {
+			return withErr(fmt.Errorf("failed to parse docker tag: %s", image.tag))
+		}
+
+		// "fn61/varasto" => "varasto"
+		imageBasename := path.Base(parsed.Repository)
+
+		lines = append(lines, "## Image: "+imageBasename, "", "```", image.tag, "```", "", "")
+	}
+
+	if _, err := stepSummaryFile.Write([]byte(strings.Join(lines, "\n"))); err != nil {
+		return withErr(err)
+	}
+
+	return nil
+}

cmd/bob/utils_test.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/function61/gokit/testing/assert"
+)
+
+func TestGithubStepSummaryWriteImages(t *testing.T) {
+	output := &bytes.Buffer{}
+
+	assert.Ok(t, githubStepSummaryWriteImages(output, []imageBuildOutput{
+		{tag: "fn61/varasto:v1.2.3"},
+		{tag: "fn61/varasto-somethingelse:v1.2.3"},
+	}))
+
+	assert.EqualString(t, output.String(), "## Image: varasto\n\n```\nfn61/varasto:v1.2.3\n```\n\n\n## Image: varasto-somethingelse\n\n```\nfn61/varasto-somethingelse:v1.2.3\n```\n\n")
+}