introduce internal support for walking multiple version schemes, needs refinement

1 files changed, 36 insertions, 8 deletions

diff --git a/src/setuptools_scm/version.py b/src/setuptools_scm/version.py
index ce21b26..ad5a18f 100644
--- a/src/setuptools_scm/version.py
+++ b/src/setuptools_scm/version.py
@@ -344,19 +344,47 @@ def postrelease_version(version):
         return version.format_with("{tag}.post{distance}")
 
 
+def _get_ep(group, name):
+    for ep in iter_entry_points(group, name):
+        trace("ep found:", ep.name)
+        return ep.load()
+
+
+def _iter_version_schemes(entrypoint, scheme_value, _memo=None):
+    if _memo is None:
+        _memo = set()
+    if isinstance(scheme_value, str):
+        scheme_value = _get_ep(entrypoint, scheme_value)
+
+    if isinstance(scheme_value, (list, tuple)):
+        for variant in scheme_value:
+            if variant not in _memo:
+                _memo.add(variant)
+                yield from _iter_version_schemes(entrypoint, variant, _memo=_memo)
+    elif callable(scheme_value):
+        yield scheme_value
+
+
+def _call_version_scheme(version, entypoint, given_value, default):
+    for scheme in _iter_version_schemes(entypoint, given_value):
+        result = scheme(version)
+        if result is not None:
+            return result
+    return default
+
+
 def format_version(version, **config):
     trace("scm version", version)
     trace("config", config)
     if version.preformatted:
         return version.tag
-    version_scheme = callable_or_entrypoint(
-        "setuptools_scm.version_scheme", config["version_scheme"]
+    main_version = _call_version_scheme(
+        version, "setuptools_scm.version_scheme", config["version_scheme"], None
     )
-    local_scheme = callable_or_entrypoint(
-        "setuptools_scm.local_scheme", config["local_scheme"]
-    )
-    main_version = version_scheme(version)
     trace("version", main_version)
-    local_version = local_scheme(version)
+    assert main_version is not None
+    local_version = _call_version_scheme(
+        version, "setuptools_scm.local_scheme", config["local_scheme"], "+unknown"
+    )
     trace("local_version", local_version)
-    return version_scheme(version) + local_scheme(version)
+    return main_version + local_version