ensure nil step does not cause problems

engine/linter/linter.go

@@ -77,6 +77,9 @@ func checkPipeline(pipeline *resource.Pipeline, trusted bool) error {
 func checkSteps(pipeline *resource.Pipeline, trusted bool) error {
 	steps := append(pipeline.Services, pipeline.Steps...)
 	for _, step := range steps {
+		if step == nil {
+			return errors.New("linter: nil step")
+		}
 		if err := checkStep(step, trusted); err != nil {
 			return err
 		}

engine/resource/parser.go

@@ -39,6 +39,9 @@ func lint(pipeline *Pipeline) error {
 	// ensure pipeline steps are not unique.
 	names := map[string]struct{}{}
 	for _, step := range pipeline.Steps {
+		if step == nil {
+			return errors.New("Linter: detected nil step")
+		}
 		if step.Name == "" {
 			return errors.New("Linter: invalid or missing step name")
 		}

engine/resource/parser_test.go

@@ -105,6 +105,14 @@ func TestParseLintErr(t *testing.T) {
 	}
 }
 
+func TestParseLintNilStep(t *testing.T) {
+	_, err := manifest.ParseFile("testdata/nilstep.yml")
+	if err == nil {
+		t.Errorf("Expect linter returns error")
+		return
+	}
+}
+
 func TestParseNoMatch(t *testing.T) {
 	r := &manifest.RawResource{Kind: "pipeline", Type: "exec"}
 	_, match, _ := parse(r)

engine/resource/testdata/nilstep.yml

@@ -0,0 +1,9 @@
+---
+kind: pipeline
+type: docker
+name: test
+
+steps:
+- ~
+
+...

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/drone/drone-runtime v1.0.7-0.20190729202838-87c84080f4a1
 	github.com/drone/drone-yaml v1.2.2
 	github.com/drone/envsubst v1.0.2
-	github.com/drone/runner-go v1.2.3-0.20191017212814-48a0db6f4ed7
+	github.com/drone/runner-go v1.2.3-0.20191017224419-ef1504fb90be
 	github.com/drone/signal v1.0.0
 	github.com/ghodss/yaml v1.0.0
 	github.com/google/go-cmp v0.3.0

go.sum

@@ -53,6 +53,8 @@ github.com/drone/runner-go v1.2.3-0.20191008184914-35b0486b7f23 h1:sj9myNBjsR7C6
 github.com/drone/runner-go v1.2.3-0.20191008184914-35b0486b7f23/go.mod h1:GvB5hX023g0n5UZUjMBmudk6givdDDuLcls7Nolm5v8=
 github.com/drone/runner-go v1.2.3-0.20191017212814-48a0db6f4ed7 h1:qGsY45PRwKdbaKZqa2jswjS5nbLEp1sDXFbVaIcbi4I=
 github.com/drone/runner-go v1.2.3-0.20191017212814-48a0db6f4ed7/go.mod h1:GvB5hX023g0n5UZUjMBmudk6givdDDuLcls7Nolm5v8=
+github.com/drone/runner-go v1.2.3-0.20191017224419-ef1504fb90be h1:tk4tW92ajKvIxlepMUX0iOAJ0CFdO5x3LsKP0H30OMs=
+github.com/drone/runner-go v1.2.3-0.20191017224419-ef1504fb90be/go.mod h1:GvB5hX023g0n5UZUjMBmudk6givdDDuLcls7Nolm5v8=
 github.com/drone/signal v1.0.0 h1:NrnM2M/4yAuU/tXs6RP1a1ZfxnaHwYkd0kJurA1p6uI=
 github.com/drone/signal v1.0.0/go.mod h1:S8t92eFT0g4WUgEc/LxG+LCuiskpMNsG0ajAMGnyZpc=
 github.com/ghodss/yaml v1.0.0 h1:wQHKEahhL6wmXdzwWG11gIVCkOv05bNOh+Rxn0yngAk=