Support relative paths in hydra-build-products to enable relocatable derivations
Is your feature request related to a problem? Please describe.
Currently, hydra-build-products requires absolute store paths in the path field. This prevents derivation outputs that are perfectly relocatable from verifying this fact, as specifying build products forces them to contain self-references.
For example, a derivation output at /nix/store/abc-foo must write:
doc none /nix/store/abc-foo/manual.pdf
This absolute path creates a self-reference in the output, making it non-relocatable even if the output would otherwise be position-independent.
The validation in src/hydra-queue-runner/build-result.cc:88 explicitly rejects non-absolute paths:
if (product.path == "" || product.path[0] != '/') continue;
Describe the solution you'd like
Support relative paths in hydra-build-products that are resolved relative to the output path. For example:
This would be resolved to $out/manual.pdf internally by Hydra, allowing the derivation to remain relocatable while still declaring its build products.
Alternatively, support an explicit output-relative syntax like:
Describe alternatives you've considered
- Status quo: Continue requiring absolute paths, accepting that all derivations with build products will have self-references
- Store-path-relative paths: Allow paths like
abc-foo/manual.pdf that are relative to the store directory, though this still encodes the hash
- Special sentinel paths: Use a placeholder like
@OUTPUT@/manual.pdf that Hydra replaces, though this is more complex
Additional context
This issue affects reproducibility and content-addressability efforts, where minimizing self-references is important for enabling features like:
- Content-addressed derivations that can be deduplicated across different store paths
- Binary cache sharing where outputs might be relocated
- Verification that outputs are truly position-independent
Related code: src/hydra-queue-runner/build-result.cc:84-90
cc @Ericson2314
Support relative paths in hydra-build-products to enable relocatable derivations
Is your feature request related to a problem? Please describe.
Currently, hydra-build-products requires absolute store paths in the path field. This prevents derivation outputs that are perfectly relocatable from verifying this fact, as specifying build products forces them to contain self-references.
For example, a derivation output at
/nix/store/abc-foomust write:This absolute path creates a self-reference in the output, making it non-relocatable even if the output would otherwise be position-independent.
The validation in
src/hydra-queue-runner/build-result.cc:88explicitly rejects non-absolute paths:Describe the solution you'd like
Support relative paths in hydra-build-products that are resolved relative to the output path. For example:
This would be resolved to
$out/manual.pdfinternally by Hydra, allowing the derivation to remain relocatable while still declaring its build products.Alternatively, support an explicit output-relative syntax like:
Describe alternatives you've considered
abc-foo/manual.pdfthat are relative to the store directory, though this still encodes the hash@OUTPUT@/manual.pdfthat Hydra replaces, though this is more complexAdditional context
This issue affects reproducibility and content-addressability efforts, where minimizing self-references is important for enabling features like:
Related code:
src/hydra-queue-runner/build-result.cc:84-90cc @Ericson2314