fix: No warning emitting in case of SCM error when fallback_version is used. Fixes #293

Signed-off-by: Frost Ming <me@frostming.com>

Author: frostming

src/pdm/backend/hooks/version/__init__.py

@@ -17,6 +17,10 @@
 )
 from pdm.backend.utils import evaluate_module_attribute
 
+_fallback_version_warning = (
+    "Can't get a valid version from {}, use fallback_version instead."
+)
+
 
 class DynamicVersionBuildHook:
     """Dynamic version implementation.
@@ -102,6 +106,7 @@ def resolve_version_from_scm(
             )
             if scm_version is None:
                 if fallback_version is not None:
+                    warnings.warn(_fallback_version_warning.format("scm"), PDMWarning)
                     version = fallback_version
                 else:
                     raise ConfigError(
@@ -119,6 +124,7 @@ def resolve_version_from_scm(
             parsed_version = Version(version)
         except ValueError:
             if fallback_version is not None:
+                warnings.warn(_fallback_version_warning.format("scm"), PDMWarning)
                 return Version(fallback_version)
             raise ConfigError(
                 f"Invalid version {version}, it must comply with PEP 440. \n"
@@ -162,6 +168,7 @@ def resolve_version_from_call(
         version = version_getter(*args)
         if version is None:
             if fallback_version is not None:
+                warnings.warn(_fallback_version_warning.format("call"), PDMWarning)
                 return Version(fallback_version)
             else:
                 raise ConfigError(