forgejo: document ifcmerge mergeability — bare repo gitattributes finding

Investigation confirmed: Forgejo's git merge-tree --write-tree (git ≥2.38)
does invoke configured merge drivers for .ifc files.

Key finding: bare repositories do NOT read committed .gitattributes — the
merge driver is silently skipped without a system-wide core.attributesFile.

Changes:
- server-config/gitattributes: new file to deploy at /etc/gitattributes,
  containing "*.ifc merge=ifcmerge"
- server-config/gitconfig-ifcmerge: adds [core] attributesFile = /etc/gitattributes
  and explains the bare-repo constraint
- forgejo/README.md: rewrites ifcmerge section with investigation findings,
  deployment steps, and distinction between server-side vs client-side setup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Bruno Postle 2026-04-24 09:27:56 +01:00
parent e824f9fd0e
commit 27883e468e
4 changed files with 74 additions and 35 deletions

View file

@ -29,7 +29,7 @@
{"id":"ifcurl-bqt","title":"Phase 4: Bonsai IFCDOCUMENTREFERENCE federation via ifc://","description":"When opening a model via ifc://, resolve IFCDOCUMENTREFERENCE locations using the repo and ref from the root file's URL as context. Resolve ifc:// locations in linked model references recursively. Requires the Phase 4 protocol handler (ifcurl-0oj).","status":"deferred","priority":3,"issue_type":"feature","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:56Z","created_by":"Bruno Postle","updated_at":"2026-04-23T06:15:11Z","defer_until":"2026-12-01T00:00:00Z","dependencies":[{"issue_id":"ifcurl-bqt","depends_on_id":"ifcurl-0oj","type":"blocks","created_at":"2026-04-23T06:49:02Z","created_by":"Bruno Postle","metadata":"{}"}],"dependency_count":1,"dependent_count":1,"comment_count":0}
{"id":"ifcurl-lcr","title":"Phase 4: Bonsai 'Copy view URL' button","description":"Add a button to Bonsai that generates an ifc:// URL from the current state: git remote/ref/file path, active selection as IfcOpenShell selector, current camera as camera+fov or scale params in IFC world coordinates, active clipping planes as clip params, current visibility mode. Default to commit hash ref; secondary option for @heads/ ref.","status":"deferred","priority":3,"issue_type":"feature","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:55Z","created_by":"Bruno Postle","updated_at":"2026-04-23T06:15:10Z","defer_until":"2026-12-01T00:00:00Z","dependencies":[{"issue_id":"ifcurl-lcr","depends_on_id":"ifcurl-0oj","type":"blocks","created_at":"2026-04-23T06:49:01Z","created_by":"Bruno Postle","metadata":"{}"}],"dependency_count":1,"dependent_count":0,"comment_count":0}
{"id":"ifcurl-0oj","title":"Phase 4: Bonsai ifc:// OS protocol handler","description":"Register ifc:// as an OS protocol handler in Bonsai on installation (Windows, macOS, Linux). On receiving a URL, resolve the git source, load the model, and apply the view state from the URL parameters (camera, selector, clipping planes, visibility mode). This is the foundation for all other Phase 4 work.","status":"deferred","priority":3,"issue_type":"feature","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:45Z","created_by":"Bruno Postle","updated_at":"2026-04-23T06:15:09Z","defer_until":"2026-12-01T00:00:00Z","dependency_count":0,"dependent_count":3,"comment_count":0}
{"id":"ifcurl-cyw","title":"Phase 3c: Verify Forgejo merge-ability check works with ifcmerge","description":"Investigate whether Forgejo's merge-ability check (the 'branches can be merged automatically' indicator) correctly reflects ifcmerge's ability to handle .ifc files. Determine if Forgejo runs a trial git merge or uses a heuristic. If needed, patch Forgejo to run a trial git merge --no-commit to get an accurate result.","status":"open","priority":3,"issue_type":"task","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:22Z","created_by":"Bruno Postle","updated_at":"2026-04-23T05:48:22Z","dependencies":[{"issue_id":"ifcurl-cyw","depends_on_id":"ifcurl-c69","type":"blocks","created_at":"2026-04-23T06:48:29Z","created_by":"Bruno Postle","metadata":"{}"}],"dependency_count":1,"dependent_count":0,"comment_count":0}
{"id":"ifcurl-cyw","title":"Phase 3c: Verify Forgejo merge-ability check works with ifcmerge","description":"Investigate whether Forgejo's merge-ability check (the 'branches can be merged automatically' indicator) correctly reflects ifcmerge's ability to handle .ifc files. Determine if Forgejo runs a trial git merge or uses a heuristic. If needed, patch Forgejo to run a trial git merge --no-commit to get an accurate result.","status":"closed","priority":3,"issue_type":"task","assignee":"Bruno Postle","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:22Z","created_by":"Bruno Postle","updated_at":"2026-04-24T08:27:25Z","started_at":"2026-04-24T08:19:58Z","closed_at":"2026-04-24T08:27:25Z","close_reason":"Verified: git merge-tree --write-tree (Forgejo's code path for git ≥2.38) does invoke merge drivers. Bare repos require core.attributesFile in /etc/gitconfig — committed .gitattributes not read. Added gitattributes server-config file and updated deployment docs.","dependencies":[{"issue_id":"ifcurl-cyw","depends_on_id":"ifcurl-c69","type":"blocks","created_at":"2026-04-23T06:48:29Z","created_by":"Bruno Postle","metadata":"{}"}],"dependency_count":1,"dependent_count":0,"comment_count":0}
{"id":"ifcurl-c69","title":"Phase 3c: Register ifcmerge as git merge driver on Forgejo server","description":"Configure ifcmerge as the git merge driver for .ifc files on the Forgejo server. Add to /etc/gitconfig or ~forgejo/.gitconfig: [merge \"ifcmerge\"] name = IFC merge driver / driver = ifcmerge %O %A %B %L. Add *.ifc merge=ifcmerge to server-side gitattributes. This allows Forgejo's 'merge automatically' path to invoke ifcmerge via git when merging .ifc files.","status":"closed","priority":3,"issue_type":"task","owner":"bruno@postle.net","created_at":"2026-04-23T05:48:21Z","created_by":"Bruno Postle","updated_at":"2026-04-24T08:15:20Z","closed_at":"2026-04-24T08:15:20Z","close_reason":"Documented ifcmerge driver registration (gitconfig-ifcmerge), gitattributes setup, merge direction constraint, and merge-commit strategy requirement","comments":[{"id":"019dbc54-bf0a-76e2-b64d-7d1681f0c730","issue_id":"ifcurl-c69","author":"Bruno Postle","text":"ifcmerge needs to be installed as a pair of merge tools because the merge process is asymmetrical and we need to be able to prefer one branch over another (because step-ids from one branch get rewritten in the merged file). In practice we prefer origin and/or main/master branches. there is code in the ifcopenshell bonsai ifcgit module for reference.","created_at":"2026-04-23T21:52:44Z"}],"dependency_count":0,"dependent_count":1,"comment_count":1}
{"id":"ifcurl-8ns","title":"Future: Contribute ifc:// URL parsing to IfcOpenShell","description":"Once the Python core URL parsing and resolution logic is stable, contribute it to IfcOpenShell as a shared utility. Not a prerequisite for any phase — pursue after Phase 1 has been stable in production use for a while.","status":"open","priority":4,"issue_type":"task","owner":"bruno@postle.net","created_at":"2026-04-23T05:49:33Z","created_by":"Bruno Postle","updated_at":"2026-04-23T05:49:33Z","dependency_count":0,"dependent_count":0,"comment_count":0}
{"id":"ifcurl-9yr","title":"Future: BCF export endpoint /bcf","description":"Add a /bcf endpoint to the preview service: POST /bcf with body {url: 'ifc://...'} returns a BCF zip file. Resolve the selector to a GUID set and construct a BCF viewpoint from the camera, clipping planes, and visibility state. Not planned before Phase 2 is complete.","status":"open","priority":4,"issue_type":"feature","owner":"bruno@postle.net","created_at":"2026-04-23T05:49:25Z","created_by":"Bruno Postle","updated_at":"2026-04-23T05:49:25Z","dependency_count":0,"dependent_count":0,"comment_count":0}

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@ -27,7 +27,8 @@ forgejo/
footer.tmpl ← "View in 3D" button injection
server-config/
ifcurl-preview.service ← systemd unit for the preview service
gitconfig-ifcmerge ← git merge driver config for .ifc files
gitconfig-ifcmerge ← git merge driver registration for /etc/gitconfig
gitattributes ← system-wide gitattributes for bare repos
```
---
@ -188,6 +189,18 @@ no preview image.
Configuring `ifcmerge` as the git merge driver for `.ifc` files lets Forgejo
automatically merge IFC pull requests instead of marking them as conflicted.
### How Forgejo checks mergeability
Forgejo (with git ≥ 2.38) uses `git merge-tree --write-tree` to perform a
trial merge in the bare repository. This command **does** invoke configured
merge drivers — confirmed by testing. With ifcmerge set up correctly,
the "can be automatically merged" indicator on a PR reflects ifcmerge's
actual result, not a naive text-conflict check.
**Important:** bare repositories do not read committed `.gitattributes` files
from the tree. The merge driver must be declared via a system-wide
`core.attributesFile` setting in `/etc/gitconfig`.
### Prerequisites
`ifcmerge` is a single Perl script from
@ -206,37 +219,23 @@ Verify it is on `PATH` for the `forgejo` system user:
sudo -u forgejo which ifcmerge
```
### Register the merge drivers
Append `server-config/gitconfig-ifcmerge` to the server's global git config:
### Deploy the config files
```bash
sudo git config --system --add include.path /path/to/forgejo/server-config/gitconfig-ifcmerge
# System-wide gitattributes (the critical piece for bare repos)
sudo cp forgejo/server-config/gitattributes /etc/gitattributes
# Append merge driver registration + core.attributesFile to /etc/gitconfig
sudo git config --system include.path /path/to/ifcurl/forgejo/server-config/gitconfig-ifcmerge
```
Or copy the two `[merge "…"]` blocks directly into `/etc/gitconfig`.
### Set the per-repository gitattributes
Add a `.gitattributes` file to each IFC repository:
```
*.ifc merge=ifcmerge
```
Or set a server-wide default by adding to
`/usr/share/git-core/templates/info/attributes` (applied to all newly
initialised repos):
```
*.ifc merge=ifcmerge
```
Or apply the blocks from `server-config/gitconfig-ifcmerge` directly into
`/etc/gitconfig` by hand.
### Merge direction
The merge driver is asymmetrical: `ifcmerge` rewrites STEP IDs from `%B`
(theirs) to match `%A` (ours), so `%A`'s ID space is preserved in the
merged file.
(theirs) to match `%A` (ours), so `%A`'s ID space is preserved.
For Forgejo, use the **"Merge commit"** strategy (not rebase or squash).
With a merge commit, `%A` is always the base branch (e.g. `main`) and
@ -244,9 +243,23 @@ With a merge commit, `%A` is always the base branch (e.g. `main`) and
existing cross-references remain valid.
A second driver `ifcmerge_ours` is defined in the config file for cases
where the base branch arrives as `%B`; see the comments in
where the base branch arrives as `%B`; see comments in
`server-config/gitconfig-ifcmerge` for details.
### Client-side `.gitattributes`
For client-side merges (`git merge` on a developer's machine) committed
`.gitattributes` files in the repository work fine. It is still worth
adding one:
```
*.ifc merge=ifcmerge
```
This ensures developers with ifcmerge installed get automatic IFC merges
locally, and tools that read gitattributes (e.g. diff viewers) can
identify `.ifc` files correctly.
---
## Upgrading Forgejo

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@ -0,0 +1,12 @@
# System-wide gitattributes for the Forgejo server.
# Reference this file from /etc/gitconfig:
#
# [core]
# attributesFile = /etc/gitattributes
#
# This causes git merge-tree --write-tree (used by Forgejo's mergeability
# check) to invoke ifcmerge for .ifc files in bare repositories.
# Committed per-repo .gitattributes files are NOT read by git in bare-repo
# context and are therefore insufficient for the server-side conflict check.
*.ifc merge=ifcmerge

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@ -1,14 +1,28 @@
# Add to /etc/gitconfig (or ~forgejo/.gitconfig) on the Forgejo server.
# Add to /etc/gitconfig on the Forgejo server.
#
# Two drivers are registered because the merge is asymmetrical — ifcmerge
# rewrites STEP IDs from %B to match %A's ID space. The base-branch must
# always be %A so its IDs are preserved.
# IMPORTANT: also set core.attributesFile so that bare repositories pick up
# the merge driver. Committed per-repo .gitattributes files are NOT read by
# git merge-tree --write-tree in bare-repo context.
#
# ifcmerge — use when the base branch is %A (standard 'merge commit')
# ifcmerge_ours — use when the base branch is %B (rebase direction);
# swaps the roles so base-branch IDs are still preserved.
# Requires ifcmerge to support --prefer-other; if not,
# use 'merge commit' strategy exclusively and omit this.
# [core]
# attributesFile = /etc/gitattributes
#
# and put "*.ifc merge=ifcmerge" in /etc/gitattributes (see gitattributes
# in this directory).
#
# How the merge drivers work
# --------------------------
# ifcmerge rewrites STEP IDs from %B to match %A's ID space, so %A's IDs
# are preserved in the merged result. Use the "Merge commit" strategy in
# Forgejo so that %A is always the base branch (e.g. main).
#
# Two variants are registered for symmetry:
# ifcmerge — base branch is %A (standard merge-commit direction)
# ifcmerge_ours — base branch is %B (rebase direction); swaps %A/%B so
# base-branch IDs are still preserved
[core]
attributesFile = /etc/gitattributes
[merge "ifcmerge"]
name = IFC merge driver (base is ours)