feat: Tanka version constraint (#396)

Adds `spec.versions.tanka` to validate the current Tanka version against
a SemVer constraint (e.g. `>=0.12`).

This is a struct and not a top level field to allow for extending in the
future, as there are other versions we could validate as well (Helm,
Kubectl, etc)

Makefile

@@ -14,7 +14,7 @@ test:
 dev:
 	go build -ldflags "-X main.Version=dev-${VERSION}" ./cmd/tk
 
-LDFLAGS := '-s -w -extldflags "-static" -X main.Version=${VERSION}'
+LDFLAGS := '-s -w -extldflags "-static" -X github.com/grafana/tanka/pkg/tanka.CURRENT_VERSION=${VERSION}'
 static:
 	CGO_ENABLED=0 go build -ldflags=${LDFLAGS} ./cmd/tk
 

cmd/tk/main.go

@@ -13,12 +13,9 @@ import (
 	"github.com/grafana/tanka/pkg/jsonnet/jpath"
 	"github.com/grafana/tanka/pkg/spec"
 	"github.com/grafana/tanka/pkg/spec/v1alpha1"
+	"github.com/grafana/tanka/pkg/tanka"
 )
 
-// Version is the current version of the tk command.
-// To be overwritten at build time
-var Version = "dev"
-
 // describing variables
 var (
 	verbose     = false
@@ -31,7 +28,7 @@ func main() {
 	rootCmd := &cli.Command{
 		Use:     "tk",
 		Short:   "tanka <3 jsonnet",
-		Version: Version,
+		Version: tanka.CURRENT_VERSION,
 	}
 
 	// workflow commands

pkg/spec/v1alpha1/config.go

@@ -54,7 +54,14 @@ type Spec struct {
 	Namespace        string           `json:"namespace"`
 	DiffStrategy     string           `json:"diffStrategy,omitempty"`
 	InjectLabels     bool             `json:"injectLabels,omitempty"`
-	ResourceDefaults ResourceDefaults `json:"resourceDefaults,omitempty"`
+	ResourceDefaults ResourceDefaults `json:"resourceDefaults"`
+	ExpectVersions   ExpectVersions   `json:"expectVersions"`
+}
+
+// ExpectVersions holds semantic version constraints
+// TODO: extend this to handle more than Tanka
+type ExpectVersions struct {
+	Tanka string `json:"tanka,omitempty"`
 }
 
 // ResourceDefaults will be inserted in any manifests that tanka processes.

pkg/tanka/parse.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"path/filepath"
 
+	"github.com/Masterminds/semver"
 	"github.com/pkg/errors"
 
 	"github.com/grafana/tanka/pkg/jsonnet"
@@ -17,6 +18,13 @@ import (
 	"github.com/grafana/tanka/pkg/spec/v1alpha1"
 )
 
+// DEFAULT_DEV_VERSION is the placeholder version used when no actual semver is
+// provided using ldflags
+const DEFAULT_DEV_VERSION = "dev"
+
+// CURRENT_VERSION is the current version of the running Tanka code
+var CURRENT_VERSION = DEFAULT_DEV_VERSION
+
 // loaded is the final result of all processing stages:
 // 1. jpath.Resolve: Consruct import paths
 // 2. parseSpec: load spec.json
@@ -61,6 +69,10 @@ func load(dir string, opts Opts) (*loaded, error) {
 		return nil, err
 	}
 
+	if err := checkVersion(env.Spec.ExpectVersions.Tanka); err != nil {
+		return nil, err
+	}
+
 	rec, err := process.Process(raw, *env, opts.Filters)
 	if err != nil {
 		return nil, err
@@ -149,3 +161,28 @@ func evalJsonnet(baseDir string, env *v1alpha1.Config, opts jsonnet.Opts) (inter
 	}
 	return data, nil
 }
+
+func checkVersion(constraint string) error {
+	if constraint == "" {
+		return nil
+	}
+	if CURRENT_VERSION == DEFAULT_DEV_VERSION {
+		return nil
+	}
+
+	c, err := semver.NewConstraint(constraint)
+	if err != nil {
+		return fmt.Errorf("Parsing version constraint: '%w'. Please check 'spec.expectVersions.tanka'", err)
+	}
+
+	v, err := semver.NewVersion(CURRENT_VERSION)
+	if err != nil {
+		return fmt.Errorf("'%s' is not a valid semantic version: '%w'.\nThis likely means your build of Tanka is broken, as this is a compile-time value. When in doubt, please raise an issue", CURRENT_VERSION, err)
+	}
+
+	if !c.Check(v) {
+		return fmt.Errorf("Current version '%s' does not satisfy the version required by the environment: '%s'. You likely need to use another version of Tanka", CURRENT_VERSION, constraint)
+	}
+
+	return nil
+}