> ## Documentation Index
> Fetch the complete documentation index at: https://tally.wharflab.com/llms.txt
> Use this file to discover all available pages before exploring further.

# hadolint/DL3022

> `COPY --from` should reference a previously defined `FROM` alias.

`COPY --from` should reference a previously defined `FROM` alias.

| Property | Value       |
| -------- | ----------- |
| Severity | Warning     |
| Category | Correctness |
| Default  | Off         |

## Description

When using multi-stage builds, `COPY --from` should reference a stage alias that was previously defined with `FROM ... AS <alias>`. Trying to copy
from a missing image alias results in an error at build time.

### Why default Off

This rule is off by default because it does not account for
[`--build-context`](https://docs.docker.com/reference/cli/docker/buildx/build/#build-context)
sources. As per the official Dockerfile documentation:

> You can also copy files directly from named contexts
> (specified with `--build-context <name>=<source>`) or images.

Since named build contexts are supplied at build time (`docker buildx build --build-context name=path`), a static linter cannot verify whether a
`COPY --from=name` reference is valid. Flagging these as violations produces
false positives that cannot be resolved without running the actual build.

To enable this rule, set its severity explicitly in your `.tally.toml`:

```toml theme={null}
[rules.hadolint.DL3022]
severity = "warning"
```

## Examples

### Problematic code

```dockerfile theme={null}
FROM debian:jesse
RUN stuff

FROM debian:jesse
COPY --from=build some stuff ./
```

### Correct code

```dockerfile theme={null}
FROM debian:jesse as build
RUN stuff

FROM debian:jesse
COPY --from=build some stuff ./
```

## References

* [hadolint/DL3022](https://github.com/hadolint/hadolint/wiki/DL3022)
* [`COPY --from`](https://docs.docker.com/reference/dockerfile/#copy---from)