bazelbuild / bazelbuild/rules_java
Unable to use stamp information in `java_binary`'s MANIFEST.MF
- Dominant language
- Starlark
- Stars
- 103
- Forks
- 102
- PR merge metrics
- No merged PRs in 30d
Description
As far as I can tell, it currently isn't possible to use the output from `--workspace_status_command` in `java_*` rules. Specifically, it seems like a fairly common use-case (and coincidentally, what I'm currently trying to do 😉) would be to include some form of build information (revision / build date / whatever) in the `MANIFEST.MF` of a `.jar` file.
**Expected behaviour**: able to `--stamp` a `java_binary` with custom variables
**Actual behaviour**: unable to pass through any custom variables to `deploy_manifest_lines`
**Steps to reproduce**:
As a fairly trivial reproduction:
```starlark
# .bazelrc
common --stamp --workspace_status_command=/usr/bin/true --embed_label="Hello"
```
```starlark
# BUILD.bazel
java_binary(name = "test", ..., deploy_manifest_lines = [ "Custom-Label: {{BUILD_EMBED_LABEL}}" ])
```
Running `bazel build :test_deploy.jar && unzip -p bazel-bin/test_deploy.jar META-INF/MANIFEST.MF` outputs:
```
...
Custom-Label: {{BUILD_EMBED_LABEL}}
...
```
rather than the desired:
```
...
Custom-Label: Hello
...
```
**Extra information**
I'm not 100% sure if this has changed in newer versions of `rules_java` (having a quick glance at the source, it seemed not?) but at least as of v7.x the attribute for `deploy_manifest_lines` only accepts a `list` of strings, and states:
> The contents of this attribute are not subject to "Make variable" substitution.
It seems like there are maybe two related problems*, one is specific to `rules_java` and the other is a more general Bazel thing:
1. `java_binary` only accepts fixed strings for `deploy_manifest_lines`
2. Bazel does not provide _convenient_ access to workspace status vars in macros or custom rules.
From what I've seen in some other places (e.g. `rules_oci`) there's no good solution to (2), so the pattern seems to be to allow providing a single file to use, and then having a command that generates that file by also reading from the `bazel-out/stable-status.txt` and `bazel-out/volatile-status.txt` files, e.g.
```starlark
# BUILD.bazel
java_manifest(name = "manifest", lines = {"Custom-Label": "{{BUILD_EMBED_LABEL}}")
java_binary(name = "test", ..., deploy_manifest_lines = ":manifest")
```
`*` I imagine some people will argue this is a feature, but it doesn't feel like it from here!
If it's possible to do it without generating an intermediate file, that would be even better, but I suspect that won't be the case (at least without some major work to Bazel itself...)!
Contributor guide
Research direction
Start with the java_binary deploy_manifest_lines attribute and reproduce the issue using the .bazelrc and BUILD.bazel examples. Inspect how workspace status is exposed through bazel-out/stable-status.txt and bazel-out/volatile-status.txt, then define a supported way for custom values to reach META-INF/MANIFEST.MF and verify the result in the generated test_deploy.jar.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- java
- Domain
- build-system
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 28/100