feat(wanda): add Digest function to wanda library

[andrew-anyscale]

Adds a Digest function that computes the content-addressed digest for a
spec file without checking the cache or building the image. Build and
Digest share setup through prepareForge (dep graph + forge construction)
and resolveBuildCore (tar context hashing + base image resolution), so
no logic is duplicated between the two paths.

Topic: wanda-digest
Signed-off-by: andrew andrew@anyscale.com

[andrew-anyscale]

Reviews in this chain:
└#454 feat(wanda): add Digest function to wanda library
　└#455 feat(wanda): add digest subcommand to wanda CLI

[andrew-anyscale]

#	head	base	diff	date	summary
0	ae7dff66	0fbeb47b	diff	Mar 10 13:25 PM	2 files changed, 177 insertions(+), 14 deletions(-)
1	50233428	0fbeb47b	diff	Mar 10 13:48 PM	1 file changed, 4 insertions(+), 1 deletion(-)
2	62b6215f	0fbeb47b	diff	Mar 10 18:06 PM	1 file changed, 31 insertions(+), 26 deletions(-)
3	2b8ead37	0fbeb47b	diff	Mar 10 18:09 PM	1 file changed, 21 insertions(+), 18 deletions(-)

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new Digest function to the wanda library, enabling the computation of content-addressed digests for container specification files. This function is designed to provide the digest efficiently, bypassing the full image build and cache lookup processes. To achieve this without duplicating logic, the PR refactors existing build setup steps into shared helper functions, prepareForge and resolveBuildCore, which are now utilized by both the Build and the new Digest functionalities. This enhancement provides a streamlined way to obtain image digests, which can be crucial for content-addressable systems and build pipeline optimizations.

Highlights

• New Digest Function: Introduced a Digest function to compute content-addressed digests for spec files without triggering a full image build or cache check.
• Code Refactoring: Extracted common setup logic into prepareForge and resolveBuildCore functions, which are now shared by both Build and Digest functions, reducing code duplication.
• Comprehensive Testing: Added a suite of new tests for the Digest function, verifying its output format, determinism, and sensitivity to configuration changes like epoch and environment variables.

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Changelog

• wanda/forge.go
  • Imported the io package.
  • Refactored the Build function to utilize a new prepareForge helper.
  • Introduced prepareForge to encapsulate common setup for Build and Digest.
  • Extracted core build input resolution logic into a new resolveBuildCore method.
  • Added a new digestSpec method to the Forge struct for computing spec digests.
  • Implemented the public Digest function to compute and write content-addressed digests.
  • Adjusted error return types in refactored functions to accommodate multiple return values.
• wanda/forge_test.go
  • Added TestDigest_format to verify the output format of the Digest function.
  • Included TestDigest_deterministic to ensure consistent digest generation.
  • Added TestDigest_epochChangesDigest to confirm epoch's influence on the digest.
  • Implemented TestDigest_envFileChangesDigest to test the impact of environment file changes.
  • Created TestDigest_matchesBuildDigest to validate that Digest output aligns with Build's internal digest.

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

The code changes introduce a new Digest function to compute content-addressed digests for specifications without building images, and a prepareForge function to set up the forge and dependency graph. The forge.Build function was refactored to use the new prepareForge function. A test was added to verify that the Digest function produces the same digest that Build logs internally. The review comment points out that the found boolean returned by strings.Cut is being ignored in the test, which could lead to incorrect test results. The reviewer suggests checking the found value to ensure the digest has the expected format before proceeding with the assertion.

[aslonnie]

feels like resolveBuildInput?

[andrew-anyscale]

Cleaner, I like it!

[aslonnie]

maybe add a buildSession struct that can capture the context like forge and depGraph and input and inputCore?

[andrew-anyscale]

Good idea. forge and graph are only setup once per run, whereas input/inputCore are per-spec, so I'll bundle those two together!