version.py: guard git calls during wheel builds (sans .git)

apis/python/version.py

@@ -103,7 +103,7 @@ def lines(*cmd, drop_trailing_newline: bool = True, **kwargs) -> List[str]:
     return lns
 
 
-def line(*cmd, **kwargs) -> Optional[str]:
+def line(*cmd, **kwargs) -> str:
     """Run a command, verify exactly one line of stdout, return it."""
     lns = lines(*cmd, **kwargs)
     if len(lns) != 1:
@@ -113,8 +113,11 @@ def line(*cmd, **kwargs) -> Optional[str]:
 
 def get_latest_tag() -> Optional[str]:
     """Return the most recent local Git tag of the form `[0-9].*.*` (or `None` if none exist)."""
-    tags = lines("git", "tag", "--list", "--sort=v:refname", "[0-9].*.*")
-    return tags[-1] if tags else None
+    try:
+        tags = lines("git", "tag", "--list", "--sort=v:refname", "[0-9].*.*")
+        return tags[-1] if tags else None
+    except CalledProcessError:
+        return None
 
 
 def get_latest_remote_tag(remote: str) -> str:
@@ -133,6 +136,40 @@ def get_sha_base10() -> int:
     return int(sha, 16)
 
 
+def get_only_remote() -> Optional[str]:
+    """Find the only remote Git repository, if one exists."""
+    try:
+        remotes = lines("git", "remote")
+        if len(remotes) == 1:
+            return remotes[0]
+    except CalledProcessError:
+        pass
+    return None
+
+
+def get_default_remote() -> Optional[str]:
+    """Find a Git remote to parse a most recent release tag from.
+
+    - If the current branch tracks a remote branch, use that remote
+    - Otherwise, if there's only one remote, use that
+    - Otherwise, return `None`
+    """
+    try:
+        tracked_branch = line(
+            "git", "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{u}"
+        )
+        tracked_remote = tracked_branch.split("/")[0]
+        err(f"Parsed tracked remote {tracked_remote} from branch {tracked_branch}")
+        return tracked_remote
+    except CalledProcessError:
+        remote = get_only_remote()
+        if remote:
+            err(f"Checking tags at default/only remote {remote}")
+            return remote
+        else:
+            return None
+
+
 def get_git_version() -> Optional[str]:
     """Construct a PEP440-compatible version string that encodes various Git state.
 
@@ -174,23 +211,28 @@ def get_git_version() -> Optional[str]:
         if latest_tag:
             err(f"Git traversal returned {ver}, using latest local tag {latest_tag}")
         else:
-            try:
-                tracked_branch = line(
-                    "git", "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{u}"
-                )
-                tracked_remote = tracked_branch.split("/")[0]
-                err(
-                    f"Parsed tracked remote {tracked_remote} from branch {tracked_branch}"
-                )
-            except CalledProcessError:
-                tracked_remote = line("git", "remote")
-                err(f"Checking tags at default/only remote {tracked_remote}")
-            latest_tag = get_latest_remote_tag(tracked_remote)
-            err(
-                f"Git traversal returned {ver}, using latest tag {latest_tag} from tracked remote {tracked_remote}"
-            )
-
-        return f"{latest_tag}.post0.dev{get_sha_base10()}"
+            # Didn't find a suitable local tag, look for a tracked/default "remote", and find its
+            # latest release tag
+            tracked_remote = get_default_remote()
+            if tracked_remote:
+                try:
+                    latest_tag = get_latest_remote_tag(tracked_remote)
+                    err(
+                        f"Git traversal returned {ver}, using latest tag {latest_tag} from tracked remote {tracked_remote}"
+                    )
+                except CalledProcessError:
+                    err(f"Failed to find tags in remote {tracked_remote}")
+                    return None
+            else:
+                err("Failed to find a suitable remote for tag traversal")
+                return None
+
+        try:
+            sha_base10 = get_sha_base10()
+            return f"{latest_tag}.post0.dev{sha_base10}"
+        except CalledProcessError:
+            err("Failed to find current SHA")
+            return None
     else:
         commits = int(m.group("commits"))
         if commits:
@@ -200,7 +242,7 @@ def get_git_version() -> Optional[str]:
             return ver
 
 
-def read_release_version():
+def read_release_version() -> Optional[str]:
     try:
         with open(RELEASE_VERSION_FILE) as fd:
             ver = fd.readline().strip()