RF: Update pkg_info to work with setuptools_scm

Author: effigies

.gitattributes

@@ -1 +1,2 @@
 .git_archival.txt export-subst
+nibabel/pkg_info.py export-subst

nibabel/pkg_info.py

@@ -1,4 +1,5 @@
 import sys
+from subprocess import run
 
 from packaging.version import Version
 
@@ -8,6 +9,9 @@
     __version__ = '0+unknown'
 
 
+COMMIT_HASH = '$Format:%h$'
+
+
 def _cmp(a, b):
     """Implementation of ``cmp`` for Python 3"""
     return (a > b) - (a < b)
@@ -64,15 +68,20 @@ def cmp_pkg_version(version_str, pkg_version_str=__version__):
     return _cmp(Version(version_str), Version(pkg_version_str))
 
 
-def pkg_commit_hash(pkg_path=None):
+def pkg_commit_hash(pkg_path: str = None):
     """Get short form of commit hash
 
-    Versioneer placed a ``_version.py`` file in the package directory. This file
-    gets updated on installation or ``git archive``.
-    We inspect the contents of ``_version`` to detect whether we are in a
-    repository, an archive of the repository, or an installed package.
+    In this file is a variable called COMMIT_HASH. This contains a substitution
+    pattern that may have been filled by the execution of ``git archive``.
+
+    We get the commit hash from (in order of preference):
 
-    If detection fails, we return a not-found placeholder tuple
+    * A substituted value in ``archive_subst_hash``
+    * A truncated commit hash value that is part of the local portion of the
+      version
+    * git's output, if we are in a git repository
+
+    If all these fail, we return a not-found placeholder tuple
 
     Parameters
     ----------
@@ -86,17 +95,20 @@ def pkg_commit_hash(pkg_path=None):
     hash_str : str
        short form of hash
     """
-    versions = _version.get_versions()
-    hash_str = versions['full-revisionid'][:7]
-    if hasattr(_version, 'version_json'):
-        hash_from = 'installation'
-    elif not _version.get_keywords()['full'].startswith('$Format:'):
-        hash_from = 'archive substitution'
-    elif versions['version'] == '0+unknown':
-        hash_from, hash_str = '(none found)', '<not found>'
-    else:
-        hash_from = 'repository'
-    return hash_from, hash_str
+    if not COMMIT_HASH.startswith('$Format'):  # it has been substituted
+        return 'archive substitution', COMMIT_HASH
+    ver = Version(__version__)
+    if ver.local is not None and ver.local.startswith('g'):
+        return ver.local[1:8], 'installation'
+    # maybe we are in a repository
+    proc = run(
+        ('git', 'rev-parse', '--short', 'HEAD'),
+        capture_output=True,
+        cwd=pkg_path,
+    )
+    if proc.stdout:
+        return 'repository', proc.stdout.strip()
+    return '(none found)', '<not found>'
 
 
 def get_pkg_info(pkg_path):
@@ -112,7 +124,7 @@ def get_pkg_info(pkg_path):
     context : dict
        with named parameters of interest
     """
-    src, hsh = pkg_commit_hash()
+    src, hsh = pkg_commit_hash(pkg_path)
     import numpy
 
     return dict(