fix: Parsing fails for named multistage dockerfile using build artifact dependency

Author: gsquared94

pkg/skaffold/docker/dependencies_test.go

@@ -63,6 +63,21 @@ FROM nginx
 ADD *.go *.none /tmp/
 `
 
+const simpleArtifactDependency = `
+ARG BASE
+FROM $BASE
+COPY worker.go .
+`
+
+const multiStageArtifactDependency = `
+ARG BASE
+FROM golang:1.9.2
+COPY worker.go .
+
+FROM $BASE AS foo
+FROM foo as bar
+`
+
 const multiStageDockerfile1 = `
 FROM golang:1.9.2
 WORKDIR /go/src/github.com/r2d4/leeroy/
@@ -325,6 +340,18 @@ func TestGetDependencies(t *testing.T) {
 			workspace:   "",
 			expected:    []string{"Dockerfile", "server.go", "worker.go"},
 		},
+		{
+			description: "simple dockerfile with artifact dependency",
+			dockerfile:  simpleArtifactDependency,
+			workspace:   "",
+			expected:    []string{"Dockerfile", "worker.go"},
+		},
+		{
+			description: "multistage dockerfile with artifact dependency",
+			dockerfile:  multiStageArtifactDependency,
+			workspace:   "",
+			expected:    []string{"Dockerfile", "worker.go"},
+		},
 		{
 			description: "copy twice",
 			dockerfile:  multiCopy,

pkg/skaffold/docker/parse.go

@@ -214,15 +214,16 @@ func extractCopyCommands(nodes []*parser.Node, onlyLastImage bool, cfg Config) (
 		switch node.Value {
 		case command.From:
 			from := fromInstruction(node)
+			if from.as != "" {
+				// Stage names are case insensitive
+				stages[strings.ToLower(from.as)] = true
+			}
+
 			if from.image == "" {
 				// some build args like artifact dependencies are not available until the first build sequence has completed.
 				// skip check if there are unavailable images
 				continue
 			}
-			if from.as != "" {
-				// Stage names are case insensitive
-				stages[strings.ToLower(from.as)] = true
-			}
 
 			// If `from` references a previous stage, then the `workdir`
 			// was already changed.
@@ -324,15 +325,13 @@ func expandOnbuildInstructions(nodes []*parser.Node, cfg Config) ([]*parser.Node
 			expandedNodes = append(expandedNodes, nodes[n:m+1]...)
 			n = m + 1
 
-			if from.image == "" {
-				// some build args like artifact dependencies are not available until the first build sequence has completed.
-				// skip check if there are unavailable images
-				continue
-			}
-
 			var onbuildNodes []*parser.Node
 			if ons, found := onbuildNodesCache[strings.ToLower(from.image)]; found {
 				onbuildNodes = ons
+			} else if from.image == "" {
+				// some build args like artifact dependencies are not available until the first build sequence has completed.
+				// skip check if there are unavailable images
+				onbuildNodes = []*parser.Node{}
 			} else if ons, err := parseOnbuild(from.image, cfg); err == nil {
 				onbuildNodes = ons
 			} else if warnMsg, ok := sErrors.IsOldImageManifestProblem(err); ok && warnMsg != "" {