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Make HEAD a symbolic ref that tracks the current branch - #69
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Previously HEAD stored a bare commit hash, with no notion of a "current
branch". commit_index advanced HEAD and then every branch that happened to
point at the old commit, so committing on one branch silently moved its
siblings; checkout, reset and merge had the same ambiguity.
Model the ref graph the way Git does. A ref is now either direct
(commit_hash set) or symbolic (symbolic_target set, naming another ref).
HEAD is normally symbolic and points at the current branch (e.g. 'master');
a detached HEAD is direct. A CHECK enforces exactly one of the two columns.
New helpers in the schema fragment:
- resolve_ref(repo, name) - follow symbolic refs to a commit hash
- current_branch(repo) - the branch HEAD tracks, or NULL if detached
- set_head_symbolic / set_head_detached
- advance_head(repo, commit) - move the current branch (or detached HEAD)
Rewrites so only the current branch moves:
- init_repository: HEAD is symbolic -> master
- commit_index / cherry_pick / revert: advance_head after committing
- reset_soft / reset_mixed: advance_head
- merge_branches: advance_head for 'HEAD', else move the named branch
- checkout_branch: attach HEAD symbolically (or create then attach)
- create_branch: create at resolved HEAD without moving HEAD
- list_branches: is_current compares against current_branch()
All other HEAD readers (log, status, tag, blame, grep, whatchanged,
archive, stash, push) now resolve through resolve_ref, and gc ignores the
symbolic HEAD's NULL commit_hash when collecting roots.
Tests: add symbolic_head_test.sql (commit advances only the current branch,
siblings and master stay put, detached HEAD advances itself). Existing
assertions that read HEAD's commit_hash column now use resolve_ref('HEAD').
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Summary
Fixes the data-model flaw where committing on one branch silently moved others. Previously
HEADstored a bare commit hash with no notion of a current branch, socommit_indexadvancedHEADand every branch that happened to point at the old commit.checkout,reset, andmergeshared the same ambiguity.This models the ref graph the way Git does.
Model
A ref is now either direct (
commit_hashset) or symbolic (symbolic_targetset, naming another ref).HEADis normally symbolic and points at the current branch (e.g.master); a detached HEAD is direct. ACHECKenforces exactly one of the two columns.New helpers (in the schema fragment):
resolve_ref(repo, name)— follow symbolic refs to a commit hashcurrent_branch(repo)— the branch HEAD tracks, orNULLif detachedset_head_symbolic/set_head_detachedadvance_head(repo, commit)— move the current branch (or the detached HEAD)Behaviour changes (only the current branch moves)
init_repository: HEAD is symbolic →mastercommit_index/cherry_pick/revert:advance_headafter committingreset_soft/reset_mixed:advance_headmerge_branches:advance_headfor the defaultHEADtarget, else move the named branchcheckout_branch: attach HEAD symbolically (creating the branch first with-c)create_branch: create at resolved HEAD without moving HEADlist_branches:is_currentcompares againstcurrent_branch(), so branches sharing a commit are no longer all "current"All other HEAD readers (
get_log,get_status,create_tag,blame,grep,whatchanged,create_archive,stash_save,push) resolve throughresolve_ref, andgcignores the symbolic HEAD'sNULLcommit_hashwhen collecting reachability roots.Tests
test/sql/symbolic_head_test.sql(12 assertions): committing advances only the current branch while a sibling branch andmasterstay put;checkoutswitches the current branch; a detached HEAD advances itself and leaves every branch untouched.commit_hashcolumn were updated to useresolve_ref('HEAD')(that column isNULLfor a symbolic HEAD).make test-coreandRUN_INTEGRATION=1 RUN_PERF=1 make test-all— PASS.Notes for reviewers
refs(nullablecommit_hash, newsymbolic_target, new CHECK). FreshCREATE EXTENSIONreflects the new model; there is noALTER EXTENSION … UPDATEmigration script since 0.4.0 is regenerated from fragments and has no released consumers. Happy to add a versioned upgrade path if you'd prefer.mainand lightly overlaps the still-open fix PRs Fix "column reference is ambiguous" errors in whatchanged, merge_trees and GPG verification #65 (whatchanged), Implement revert's missing apply_inverse_diff helper #66 (revert), and Fix create_archive: operator precedence, malformed zip bytea literals, repo scoping #68 (create_archive) in the specific HEAD-resolution blocks. If those merge first I'll rebase and regenerate; the underlying changes don't conflict semantically.🤖 Generated with Claude Code
Generated by Claude Code