skip unsupported platforms

Signed-off-by: Casey Lee <cplee@nektos.com>

pkg/runner/run_context.go

@@ -24,15 +24,16 @@ import (
 
 // RunContext contains info about current job
 type RunContext struct {
-	Config      *Config
-	Matrix      map[string]interface{}
-	Run         *model.Run
-	EventJSON   string
-	Env         map[string]string
-	Tempdir     string
-	ExtraPath   []string
-	CurrentStep string
-	StepResults map[string]*stepResult
+	Config       *Config
+	Matrix       map[string]interface{}
+	Run          *model.Run
+	EventJSON    string
+	Env          map[string]string
+	Tempdir      string
+	ExtraPath    []string
+	CurrentStep  string
+	StepResults  map[string]*stepResult
+	PlatformName string
 }
 
 type stepResult struct {
@@ -55,6 +56,10 @@ func (rc *RunContext) Close(ctx context.Context) error {
 
 // Executor returns a pipeline executor for all the steps in the job
 func (rc *RunContext) Executor() common.Executor {
+	if img := platformImage(rc.PlatformName); img == "" {
+		return common.NewInfoExecutor("  \U0001F6A7  Skipping unsupported platform '%s'", rc.PlatformName)
+	}
+
 	err := rc.setupTempDir()
 	if err != nil {
 		return common.NewErrorExecutor(err)

pkg/runner/runner.go

@@ -79,6 +79,9 @@ func (runner *runnerImpl) NewRunExecutor(run *model.Run, matrix map[string]inter
 	rc.EventJSON = runner.eventJSON
 	rc.StepResults = make(map[string]*stepResult)
 	rc.Matrix = matrix
+
+	ee := rc.NewExpressionEvaluator()
+	rc.PlatformName = ee.Interpolate(run.Job().RunsOn)
 	return func(ctx context.Context) error {
 		ctx = WithJobLogger(ctx, rc.Run.String())
 		return rc.Executor()(ctx)

pkg/runner/step.go

@@ -34,7 +34,7 @@ func (rc *RunContext) newStepExecutor(step *model.Step) common.Executor {
 			containerSpec.Volumes = job.Container.Volumes
 			containerSpec.Options = job.Container.Options
 		} else {
-			containerSpec.Image = platformImage(ee.Interpolate(job.RunsOn))
+			containerSpec.Image = platformImage(rc.PlatformName)
 		}
 		return common.NewPipelineExecutor(
 			rc.setupShellCommand(containerSpec, step.Shell, step.Run),
@@ -154,7 +154,7 @@ func (rc *RunContext) setupShellCommand(containerSpec *model.ContainerSpec, shel
 }
 
 func platformImage(platform string) string {
-	switch platform {
+	switch strings.ToLower(platform) {
 	case "ubuntu-latest", "ubuntu-18.04":
 		return "ubuntu:18.04"
 	case "ubuntu-16.04":