Timeline

* Deltify predecessors on the commit path

Every locally-created artifact was stored whole. The delta table was in the schema and stayed empty, so a repository grew with the number of commits rather than the amount of change. blob.StoreDelta existed and worked but had no caller on the commit path; the only delta-store in use was blob.StoreDeltaRaw, from the sync receive path, for deltas that arrive pre-encoded. The write path never made a deltify decision at all.

Port canonical Fossil's content_deltify (2.28 src/content.c:852-947) as content.Deltify. Fossil deltifies backwards: a new artifact is always stored whole and its PREDECESSOR is rewritten as a delta against it, so the tip of every chain is full content and reading the newest version of a file stays a single blob load. Chain depth becomes an artifact's age in revisions rather than something that compounds, because an artifact already stored as a delta is never re-deltified.

blob.StoreDelta turned out to be the wrong primitive to wire up: it inserts a new row as a delta, whereas the policy needs to rewrite an existing row. It is left alone. content.Deltify lives in the content package because it needs Expand, which blob cannot import.

The policy is stated once, in content.Deltify, with each rule's canonical line cited: the 50-byte floors, the 75% ratio, the never-redeltify rule that bounds depth, the private-into-public refusal, and the loop break that undeltas the source and then still declines the pairing. Two call sites pass pairs, mirroring canonical's: insertMlinkRow for file content (manifest.c:1562) and Checkin for the parent manifest (checkin.c:3234). insertMlinkRow is shared by the fresh-commit and crosslink paths, so file deltification cannot drift between them.

On a 12-revision, 4-file history: 60 artifacts, 44 delta-encoded (73%), p50 chain depth 4, max 11, and 23,994 content bytes measured as sum(length(content)) -- down from 58,973 with everything whole. A repository produced this way passes fossil 2.28 test-integrity (60/60 blobs, 0 errors) and fossil rebuild, which re-derives every table by walking the chains.

* Bound the deltify ancestor walk, require a transaction, harden tests

Review follow-ups on the deltification policy.

Bound the ancestor walk. It was a bare loop with no cycle guard: a sync peer can shape a cyclic delta graph, because blob.StoreDeltaRaw records delta(rid,srcid) links from the wire without a cycle check, and an unbounded walk would spin inside the write transaction. Guard with the seen-set idiom content.walkDeltaChain already uses, plus a step cap. In the current ordering IsAvailable runs first on both rids and follows the same links under its own depth bound, so Deltify declines before the walk begins -- but that protection is incidental to a different question, so the bound belongs to the loop that needs it. Both behaviours are now pinned: the walk reports a cycle, and Deltify declines an ungrounded source.

Move both size floors ahead of the walk. Canonical returns on a sub-50-byte target (content.c:877-885) before entering the candidate loop, so it never reaches the content_undelta on :902. Running the walk first meant a small target whose successor chained back to it would inflate the source to full content and then decline anyway -- a storage regression and exactly the divergence from canonical's layout the surrounding comment claims to avoid.

Take *db.Tx instead of db.Querier. The rewrite is two statements, and a blob holding delta bytes with no delta row expands as though it were full content: silent corruption rather than a detectable error. Canonical wraps the pair in db_begin_transaction (content.c:938-941); the signature now makes that non-negotiable at compile time. Both call sites already passed a transaction.

Three tests were named for behaviours they did not pin, and each is now verified to fail when the behaviour is reverted:

- The 75% ratio test had no assertion at all; deleting the rule left it passing. It now asserts the pair is declined and stays whole. - The loop-break test could not distinguish declining from proceeding, so the undelta-then-proceed behaviour corrected in the previous commit was untested. It now asserts the target is left whole. - The manifest test checked only "at least one", so a regression from 11-of-12 to 3-of-12 passed. It now checks each index and names the manifest that stopped being encoded.

Also cover the source-side 50-byte floor, which the tiny-artifact test could not reach because it made both artifacts tiny and returned at the target check first, and assert that Undelta restores blob.size while Deltify leaves it alone (content.c:761 vs :935).

Gate the fossil-binary test on REQUIRE_FOSSIL_BIN, set in CI. A skip is invisible without -v, so a run with no fossil binary was byte-identical to a pass -- for the one criterion our own tests cannot substitute for.

Document that blob.StoreDelta is not the commit path's primitive. It inserts a new row as a delta; deltifying rewrites an existing one. It has no non-test callers and the package doc advertised it as the delta-storing entry point.

* Document what the deltify loop-safety argument rests on

Two comments, no behaviour change.

The IsAvailable(srcRid) guard is ours, not canonical's: content.c guards only content_is_available(rid) and then calls content_get(srcid) unguarded. It is also load-bearing beyond phantoms, because it screens out the cyclic delta graphs that would otherwise reach the ancestor walk. Say both, at the guard.

And say at the walk why its seen-set never fires in practice, so that someone reordering the prologue meets the reason rather than concluding the bound is dead code. The note lived only in the test file, which is not where that reader is looking. check-in: 2368cad91a user: [email protected] tags: trunk

* fix: distinguish absent, empty, and valued U-cards in manifest parsing

Manifest parsing collapsed a wholly absent U-card and a present-but-empty U-card into the same stored value (empty string), so every crosslink call site that wrote the check-in user into event/attachment/forumpost rows lost the distinction between "no login recorded" (should be SQL NULL) and "login explicitly blanked" (canonical fossil resolves this to the literal "anonymous" at parse time — see src/manifest.c:1008-1016).

Change deck.Deck.U from string to *string so the three states are representable: nil (absent), non-nil "anonymous" (present-empty, resolved in parseUCard the same way fossil's own parser does), and non-nil with a value (present). Resolving once in the parser means every downstream crosslink/rebuild call site can keep binding d.U directly — Go's database/sql converts a nil *string argument to SQL NULL and dereferences a non-nil one automatically, so no per-call-site special casing is needed. The type change itself makes the old ambiguous string-binding path a compile error everywhere Deck.U is constructed, closing off the drift that caused issue #29.

Added deck.Str, a small pointer-literal helper, since Go can't take the address of a string literal directly; existing tests that built Deck{U: "..."} now go through it.

* fix: review nits — whitespace U-cards, rebuild coverage, tag.AddTag, naming

Four follow-ups from review of the U-card presence fix:

- deck.parseUCard now trims args before the emptiness check, matching canonical fossil's next_token() (skips leading whitespace) and every sibling card parser in this file. Previously "U \n" stored literal whitespace instead of resolving to "anonymous". Added a whitespace-only case to TestParseUCardStates.

- Added TestRebuild_UCardPresenceStates covering the rebuild path (rebuild_manifest.go's rebuildCheckin), mirroring TestCrosslink_UCardPresenceStates. The binding site was already correct (same nil-to-NULL pointer semantics as crosslink.go) but had no dedicated regression test.

- tag.AddTag now panics on an empty opts.User, matching the panic idiom CheckinOpts.User already establishes. Previously a tag created with an empty User silently crosslinked to user=''; that asymmetry with CheckinOpts was a wart worth closing rather than documenting as intentional.

- Renamed deck.Str to deck.User: the name should say what the helper constructs (a Deck.U value), not how it's implemented (a pointer take). check-in: 527759acd5 user: [email protected] tags: trunk