adopt setuptools-scm for auto versioning

.git_archival.txt

@@ -0,0 +1,4 @@
+node: $Format:%H$
+node-date: $Format:%cI$
+describe-name: $Format:%(describe:tags=true)$
+ref-names: $Format:%D$

.gitattributes

@@ -0,0 +1 @@
+.git_archival.txt  export-subst

.gitignore

@@ -1,5 +1,8 @@
 *.py[co]
 
+# setuptools-scm
+_version.py
+
 # Environment file which should be autogenerated
 *conda_requirements.txt*
 

lib/iris/__init__.py

@@ -97,19 +97,18 @@ def callback(cube, field, filename):
 import threading
 
 import iris._constraints
-from iris._deprecation import IrisDeprecation, warn_deprecated
 import iris.config
 import iris.io
 
+from ._deprecation import IrisDeprecation, warn_deprecated
+from ._version import version as __version__  # noqa: F401
+
 try:
     import iris_sample_data
 except ImportError:
     iris_sample_data = None
 
 
-# Iris revision.
-__version__ = "3.3.dev0"
-
 # Restrict the names imported when using "from iris import *"
 __all__ = [
     "AttributeConstraint",

pyproject.toml

@@ -1,12 +1,17 @@
 [build-system]
 # Defined by PEP 518
 requires = [
-  "setuptools>=40.8.0",
+  "setuptools>=45",
+  "setuptools_scm[toml]>=6.2",
+  "setuptools_scm_git_archive",
   "wheel",
 ]
 # Defined by PEP 517
 build-backend = "setuptools.build_meta"
 
+[tool.setuptools_scm]
+write_to = "lib/iris/_version.py"
+local_scheme = "dirty-tag"
 
 [tool.black]
 line-length = 79

requirements/ci/py38.yml

@@ -7,7 +7,9 @@ dependencies:
   - python =3.8
 
 # Setup dependencies.
-  - setuptools >=40.8.0
+  - setuptools >=45
+  - setuptools_scm >=6.2
+  - setuptools_scm_git_archive
 
 # Core dependencies.
   - cartopy >=0.20

requirements/ci/py39.yml

@@ -7,7 +7,9 @@ dependencies:
   - python =3.9
 
 # Setup dependencies.
-  - setuptools >=40.8.0
+  - setuptools >=45
+  - setuptools_scm >=6.2
+  - setuptools_scm_git_archive
 
 # Core dependencies.
   - cartopy >=0.20