include source repo, revision and go package version as build-args

Signed-off-by: Avi Deitcher <avi@deitcher.net>

docs/packages.md

@@ -264,6 +264,23 @@ linuxkit pkg build --platforms=linux/arm64 --builders linux/arm64=my-remote-arm6
 
 linuxkit will try to build for `linux/arm64` using the context `my-remote-arm64`. Since that context does not exist, you will get an error.
 
+##### Preset build arguments
+
+When building packages, the following build-args automatically are set for you:
+
+* `SOURCE` - the source repository of the package
+* `REVISION` - the git commit that was used for the build
+* `GOPKGVERSION` - the go package version or pseudo-version per https://go.dev/ref/mod#glos-pseudo-version
+
+Note that the above are set **only** if you do not set them in `build.yaml`. Your settings _always_
+override these built-in ones.
+
+To use them, simply address them in your `Dockerfile`:
+
+```dockerfile
+ARG SOURCE
+```
+
 ### Build packages as a maintainer
 
 All official LinuxKit packages are multi-arch manifests and most of

src/cmd/linuxkit/pkglib/build.go

@@ -309,12 +309,23 @@ func (p Pkg) Build(bos ...BuildOpt) error {
 		if p.git != nil && p.gitRepo != "" {
 			imageBuildOpts.Labels["org.opencontainers.image.source"] = p.gitRepo
 		}
-		if p.git != nil && !p.dirty {
-			commit, err := p.git.commitHash("HEAD")
+		var (
+			gitCommit    string
+			goPkgVersion string
+		)
+		if p.git != nil {
+			if !p.dirty {
+				gitCommit, err = p.git.commitHash("HEAD")
+				if err != nil {
+					return err
+				}
+				imageBuildOpts.Labels["org.opencontainers.image.revision"] = gitCommit
+			}
+			// get the go version or pseudo-version
+			goPkgVersion, err = p.git.goPkgVersion()
 			if err != nil {
 				return err
 			}
-			imageBuildOpts.Labels["org.opencontainers.image.revision"] = commit
 		}
 
 		imageBuildOpts.NetworkMode = "default"
@@ -342,6 +353,16 @@ func (p Pkg) Build(bos ...BuildOpt) error {
 				imageBuildOpts.BuildArgs[parts[0]] = &parts[1]
 			}
 		}
+		// add in information about the build process that might be useful
+		if _, ok := imageBuildOpts.BuildArgs["SOURCE"]; !ok && p.gitRepo != "" {
+			imageBuildOpts.BuildArgs["SOURCE"] = &p.gitRepo
+		}
+		if _, ok := imageBuildOpts.BuildArgs["REVISION"]; !ok && gitCommit != "" {
+			imageBuildOpts.BuildArgs["REVISION"] = &gitCommit
+		}
+		if _, ok := imageBuildOpts.BuildArgs["GOPKGVERSION"]; !ok && goPkgVersion != "" {
+			imageBuildOpts.BuildArgs["GOPKGVERSION"] = &goPkgVersion
+		}
 
 		// build for each arch and save in the linuxkit cache
 		for _, platform := range platformsToBuild {

src/cmd/linuxkit/pkglib/git.go

@@ -211,3 +211,36 @@ func (g git) isDirty(pkg, commit string) (bool, error) {
 		return false, err
 	}
 }
+
+// goPkgVersion return a version that is compliant with go package versioning.
+// This would either be:
+//
+// - The tag name if the most recent commit is tagged
+// - The structure <version>-<count>-<commmit> if the most recent commit is not tagged
+//
+// See https://go.dev/ref/mod for more information
+func (g git) goPkgVersion() (string, error) {
+	lastSemver, _ := g.commandStdout(nil, "--no-pager", "describe", "--match='v[0-9].[0-9].[0-9]*'", "--abbrev=0", "--tags")
+	if lastSemver == "" {
+		lastSemver = "v0.0.0"
+	}
+	commitList := "HEAD"
+	if lastSemver != "v0.0.0" {
+		commitList = fmt.Sprintf("%s..HEAD", lastSemver)
+	}
+	count, err := g.commandStdout(nil, "rev-list", commitList, "--count")
+	if err != nil {
+		return "", err
+	}
+	version := ""
+	if count == "0" {
+		version = lastSemver
+	} else {
+		dateCommit, err := g.commandStdout(nil, "--no-pager", "show", "--quiet", "--abbrev=12", "--date=format-local:%Y%m%d%H%M%S", "--format=%cd-%h")
+		if err != nil {
+			return "", err
+		}
+		version = fmt.Sprintf("%s-%s", lastSemver, dateCommit)
+	}
+	return version, nil
+}

test/cases/000_build/030_build_args/test.sh

@@ -10,7 +10,7 @@ set -ex
 . "${RT_PROJECT_ROOT}/_lib/lib.sh"
 
 # Test code goes here
-echo Linuxkig is "$(which linuxkit)"
+echo Linuxkit is "$(which linuxkit)"
 RESULT="$(2>&1 linuxkit pkg build --force . | grep PASSED)"
 echo RESULT="${RESULT}"
 echo "${RESULT}" | grep  "Build-arg test PASSED"

test/cases/000_build/031_fixed_build_args/Dockerfile

@@ -0,0 +1,11 @@
+FROM alpine:3.17
+
+ARG SOURCE=FAILED
+ARG REVISION=FAILED
+ARG GOPKGVERSION=FAILED
+
+RUN echo "printf \"Build-arg test source $SOURCE\\n\"" >> check.sh
+RUN echo "printf \"Build-arg test revision $REVISION\\n\"" >> check.sh
+RUN echo "printf \"Build-arg test gopkgversion $GOPKGVERSION\\n\"" >> check.sh
+
+ENTRYPOINT ["/bin/sh", "/check.sh"]

test/cases/000_build/031_fixed_build_args/build.yml

@@ -0,0 +1,5 @@
+image: build-args-test
+network: true
+arches:
+    - amd64
+    - arm64

test/cases/000_build/031_fixed_build_args/test.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+# SUMMARY: Check that the build-args are correctly passed to Dockerfiles
+# LABELS:
+# REPEAT:
+
+set -ex
+
+# Source libraries. Uncomment if needed/defined
+#. "${RT_LIB}"
+. "${RT_PROJECT_ROOT}/_lib/lib.sh"
+
+# Test code goes here
+echo Linuxkit is "$(which linuxkit)"
+RESULT="$(2>&1 linuxkit pkg build --force . | grep 'Build-arg test' || echo)"
+echo RESULT="${RESULT}"
+echo "${RESULT}" | grep  -v "FAILED"
+
+exit 0