Resolving nested meta ARGs against themselves and build ARGs

pkg/dockerfile/dockerfile.go

@@ -58,6 +58,11 @@ func ParseStages(opts *config.KanikoOptions) ([]instructions.Stage, []instructio
  return nil, nil, errors.Wrap(err, "parsing dockerfile")
  }
 
+ metaArgs, err = expandNested(metaArgs, opts.BuildArgs)
+ if err != nil {
+ return nil, nil, errors.Wrap(err, "expanding meta ARGs")
+ }
+
  return stages, metaArgs, nil
 }
 
@@ -97,6 +102,25 @@ func Parse(b []byte) ([]instructions.Stage, []instructions.ArgCommand, error) {
  return stages, metaArgs, nil
 }
 
+// expandNestedArgs tries to resolve nested ARG value against the previously defined ARGs
+func expandNested(metaArgs []instructions.ArgCommand, buildArgs []string) ([]instructions.ArgCommand, error) {
+ prevArgs := make([]string, 0)
+ for i := range metaArgs {
+ arg := metaArgs[i]
+ v := arg.Value
+ if v != nil {
+ val, err := util.ResolveEnvironmentReplacement(*v, append(prevArgs, buildArgs...), false)
+ if err != nil {
+ return nil, err
+ }
+ prevArgs = append(prevArgs, arg.Key+"="+val)
+ arg.Value = &val
+ metaArgs[i] = arg
+ }
+ }
+ return metaArgs, nil
+}
+
 // stripEnclosingQuotes removes quotes enclosing the value of each instructions.ArgCommand in a slice
 // if the quotes are escaped it leaves them
 func stripEnclosingQuotes(metaArgs []instructions.ArgCommand) ([]instructions.ArgCommand, error) {

pkg/dockerfile/dockerfile_test.go

@@ -33,6 +33,9 @@ func Test_ParseStages_ArgValueWithQuotes(t *testing.T) {
  dockerfile := `
  ARG IMAGE="ubuntu:16.04"
  ARG FOO=bar
+ ARG HELLO="Hello"
+ ARG WORLD="World"
+ ARG NESTED="$HELLO $WORLD"
  FROM ${IMAGE}
  RUN echo hi > /hi
 
@@ -65,11 +68,11 @@ func Test_ParseStages_ArgValueWithQuotes(t *testing.T) {
  t.Fatal("length of stages expected to be greater than zero, but was zero")
  }
 
- if len(metaArgs) != 2 {
+ if len(metaArgs) != 5 {
  t.Fatalf("length of stage meta args expected to be 2, but was %d", len(metaArgs))
  }
 
- for i, expectedVal := range []string{"ubuntu:16.04", "bar"} {
+ for i, expectedVal := range []string{"ubuntu:16.04", "bar", "Hello", "World", "Hello World"} {
  if metaArgs[i].ValueString() != expectedVal {
  t.Fatalf("expected metaArg %d val to be %s but was %s", i, expectedVal, metaArgs[i].ValueString())
  }