Bonsai: expose git describe string to titleblock templates

Adds IfcGit.get_repo_description(), which returns a git-describe style
string (tags, always, dirty) for the repo containing an IFC file, or
None when GitPython is unavailable, the file isn't in a git repo, or
the repo has no commits yet.

sheeter.py's build_titleblock() now makes this available to the
pystache titleblock template render as a "GitDescribe" key, falling
back to an empty string rather than the literal word "None". This is
purely additive: sheet.get_info() itself is untouched, no shipped
titleblock SVG references the new key, and existing Revision,
Identification and Name substitution behaviour is unchanged. Users who
want the git description on their titleblock can reference
{{GitDescribe}} in their own custom titleblock SVG.

Part of the "Make revision list and most recent tag available to
drawing generation" item from issue #3096.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/bim/module/drawing/sheeter.py

@@ -319,7 +319,12 @@ class SheetBuilder:
     def build_titleblock(self, root: ET.Element, sheet: ifcopenshell.entity_instance) -> None:
         titleblock = root.findall(f'{SVG}g[@data-type="titleblock"]')[0]
         image = titleblock.findall(f"{SVG}image")[0]
-        g = self.parse_embedded_svg(image, sheet.get_info())
+        # Extend the raw IFC attribute dict with extra, non-IFC substitution
+        # keys available to custom titleblock templates. This does not
+        # change what sheet.get_info() itself returns elsewhere.
+        titleblock_data = dict(sheet.get_info())
+        titleblock_data["GitDescribe"] = tool.IfcGit.get_repo_description(tool.Ifc.get_path()) or ""
+        g = self.parse_embedded_svg(image, titleblock_data)
         grid_north = ifcopenshell.util.geolocation.get_grid_north(tool.Ifc.get()) * -1
         true_north = ifcopenshell.util.geolocation.get_true_north(tool.Ifc.get()) * -1
         for north in g.iterfind(f'.//{SVG}g[@data-type="grid-north"]'):

src/bonsai/bonsai/tool/ifcgit.py

@@ -40,8 +40,11 @@ try:
     import git
     import git.exc
     import git.objects
+
+    GIT_AVAILABLE = True
 except ImportError:
     print("Warning: GitPython not available.")
+    GIT_AVAILABLE = False
 
 if TYPE_CHECKING:
     import git
@@ -124,6 +127,25 @@ class IfcGit(bonsai.core.tool.IfcGit):
             IfcGitRepo.repo = repo
         return repo
 
+    @classmethod
+    def get_repo_description(cls, path_ifc: str) -> Union[str, None]:
+        """Return a `git describe --tags --always --dirty` style string for the
+        repository containing path_ifc (e.g. "v1.2-4-gabcdef1"), or None if
+        unavailable.
+
+        Returns None instead of raising when GitPython isn't installed, the
+        path isn't inside a git repository, or the repository has no commits.
+        """
+        if not GIT_AVAILABLE:
+            return None
+        try:
+            repo = cls.repo_from_path(path_ifc)
+            if repo is None:
+                return None
+            return repo.git.describe(tags=True, always=True, dirty=True)
+        except Exception:
+            return None
+
     @classmethod
     def add_file_to_repo(cls, repo: git.Repo, path_file: str) -> None:
         if os.name == "nt":