[ma2bd]

Motivation

linera-version/api-hashes.json has not changed since #2347 (2024-08-03), even though the WIT files, the GraphQL schema and the RPC snapshot have all changed since — this branch and main ship the same three hashes despite having different WIT files. Two things kept it that way:

• tests/up_to_date.rs compares VersionInfo::get() against VersionInfo::default(). The latter is baked in by build.rs, which calls the same trace_get, so in a workspace checkout both sides are computed from the live files and the file is never consulted. The test cannot fail.
• The command it recommends, cargo run -p linera-version > linera-version/api-hashes.json, truncates the file before the binary starts, and trace_get reads it eagerly, so regenerating fails with JSON error: EOF while parsing a value at line 1 column 0.

The file is what a published crate reports, since cargo metadata resolves it standalone there, without the sibling packages the hashes are computed from. VersionInfo::is_compatible_with compares api_hashes() before falling back to semver, so stale values let two registry builds with different APIs consider each other compatible.

Proposal

• Read the file only when a hash cannot be computed, instead of always. That is what it is for, and it makes the file writable from the tool's own output.
• Compare the computed hashes against the file in tests/up_to_date.rs.
• Add a check-outdated-api-hashes CI job, in the style of check-outdated-cli-md.
• Terminate the generated JSON with a newline, and refresh the file with this branch's own hashes.

Relationship to #6818. On main the mechanism is being removed instead: the hashes become Option, absent when they cannot be computed, and the file is deleted — because in the only situation that reads it, the recorded hashes are a constant of the release and therefore carry nothing that crate_version does not. That change alters the BCS encoding of RpcMessage::VersionInfoResponse and flips the RPC hash, which is not acceptable on a deployed network in a patch release. So this branch keeps the file and only makes it correct and verified; this is the terminal state for the 0.15 line.

Test Plan

• cargo test -p linera-version fails on the stale file before the refresh, reporting all three hashes, and passes after it.
• cargo run -p linera-version > linera-version/api-hashes.json now succeeds and is idempotent; before this change it failed on the truncated file.
• The new job's command, diff linera-version/api-hashes.json <(cargo run --locked -p linera-version), exits 0 on this branch.
• No type or wire change: linera-rpc's format snapshot is untouched.
• cargo fmt (pinned nightly-2025-04-03), cargo clippy --all-targets --all-features -p linera-version and taplo fmt --check are clean under Rust 1.86.

Release Plan

• Nothing to do / These changes follow the usual release cycle.

Links

• Report unknown API hashes instead of falling back to a committed file #6818 removes the mechanism on main.
• reviewer checklist

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