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fix: stacker convert should check if FROMAS base is in current build #2

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fix: stacker convert should check if FROMAS base is in current build #2

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25 changes: 23 additions & 2 deletions pkg/stacker/convert.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ import (
"path/filepath"
"regexp"
"runtime"
"slices"
"strconv"
"strings"

Expand Down Expand Up @@ -72,6 +73,8 @@ type Command struct {
Value []string // The contents of the command (ex: `ubuntu:xenial`)
}

var buildstages []string

Comment on lines +76 to +77

@jsatterfield-geico jsatterfield-geico Jul 28, 2026

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I'm not sure if creating a new package-level variable is appropriate here. Perhaps create a local variable in parseFile() and pass it into convertCommand() instead as an argument?

func (c *Converter) convertCommand(cmd *Command) error {
var layer *types.Layer
if c.currLayer != "" {
Expand All @@ -90,13 +93,22 @@ func (c *Converter) convertCommand(cmd *Command) error {
c.subs["IMAGE"] = "app"
} else if len(cmd.Value) == 3 && strings.EqualFold(cmd.Value[1], "as") {

@jsatterfield-geico jsatterfield-geico Jul 28, 2026 •
edited
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This tells me that Stacker does not support --platform <platform> in FROM, so maybe you don't need to support it yet.

c.currLayer = cmd.Value[2]

// Check if the base stage is in a build stage
if slices.Contains(buildstages, cmd.Value[0]) {
layer.From.Type = "built"

@jsatterfield-geico jsatterfield-geico Jul 28, 2026

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Instead of a raw string, I would use the Stacker-defined type: https://github.com/project-stacker/stacker/blob/main/pkg/types/layer.go#L25

layer.From.Tag = cmd.Value[0]
}
// layer.BuildOnly = true // FIXME: should be enabled

@jsatterfield-geico jsatterfield-geico Jul 29, 2026

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Have you looked into enabling this flag versus setting layer.From? Is there a difference between the two? Just wondering because this comment implies that they do keep track of these "build-only" stages using this flag.

I'm wondering if setting layer.From directly maybe bypasses some of that logic?

} else {
return errors.Errorf("unsupported FROM directive")

@jsatterfield-geico jsatterfield-geico Jul 28, 2026 •
edited
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And this tells me the --platform <platform> would be outright rejected. Please close the other two comments as resolved...

}
if !strings.EqualFold(cmd.Value[0], "scratch") {
layer.From.Type = "docker"
layer.From.Url = fmt.Sprintf("docker://%s", cmd.Value[0])
// Have we seen this...
if layer.From.Type != "built" {
layer.From.Type = "docker"
layer.From.Url = fmt.Sprintf("docker://%s", cmd.Value[0])
}
} else {
layer.From.Type = cmd.Value[0]
}
Expand Down Expand Up @@ -309,6 +321,15 @@ func (c *Converter) parseFile() error {
return err
}

// Collect all possible build stages before starting conversion.
for _, child := range res.AST.Children {
fields := strings.Fields(child.Original)
if fields[0] == "FROM" && len(fields) == 4 {
buildstages = append(buildstages, fields[3])
}
Comment on lines +327 to +329

@jsatterfield-geico jsatterfield-geico Jul 28, 2026

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This works for parsing FROM <image> AS <name>, but FROM --platform=<platform> <image> AS <name> is equally valid. https://docs.docker.com/reference/dockerfile/#from

Does Stacker handle multi-platform image references? If so, we should handle that use-case here.

@jsatterfield-geico jsatterfield-geico Jul 28, 2026

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I would suggest len(fields) > 4 and fields[len(fields) - 1] which should cover both.

}

// Do conversion
for _, child := range res.AST.Children {
cmd := Command{
Cmd: child.Value,
Expand Down
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