Use a clearer message for nonexistent template branches

src/briefcase/commands/base.py

@@ -32,10 +32,10 @@
 from briefcase.exceptions import (
     BriefcaseCommandError,
     BriefcaseConfigError,
+    InvalidTemplateBranch,
     InvalidTemplateRepository,
     MissingAppMetadata,
     NetworkFailure,
-    TemplateUnsupportedVersion,
     UnsupportedHostError,
     UnsupportedPythonVersion,
 )
@@ -1037,7 +1037,7 @@ def update_cookiecutter_cache(self, template: str, branch="master"):
                     head.checkout()
                 except IndexError as e:
                     # No branch exists for the requested version.
-                    raise TemplateUnsupportedVersion(branch) from e
+                    raise InvalidTemplateBranch(template, branch) from e
             except (ValueError, self.tools.git.exc.GitError) as e:
                 raise BriefcaseCommandError(
                     "Unable to check out template branch.\n"
@@ -1094,7 +1094,7 @@ def _generate_template(self, template, branch, output_path, extra_context):
             raise InvalidTemplateRepository(template) from e
         except cookiecutter_exceptions.RepositoryCloneFailed as e:
             # Branch does not exist.
-            raise TemplateUnsupportedVersion(branch) from e
+            raise InvalidTemplateBranch(template, branch) from e
         except cookiecutter_exceptions.UndefinedVariableInTemplate as e:
             raise BriefcaseConfigError(e.message) from e
 
@@ -1135,7 +1135,7 @@ def generate_template(
                 output_path=output_path,
                 extra_context=extra_context,
             )
-        except TemplateUnsupportedVersion:
+        except InvalidTemplateBranch:
             # Only use the main template if we're on a development branch of briefcase
             # and the user didn't explicitly specify which branch to use.
             if version.dev is None or branch is not None:

src/briefcase/exceptions.py

@@ -137,11 +137,10 @@ def __init__(self, error_msg):
         super().__init__(msg=error_msg, skip_logfile=True)
 
 
-class TemplateUnsupportedVersion(BriefcaseCommandError):
-    def __init__(self, briefcase_version):
-        self.briefcase_version = briefcase_version
+class InvalidTemplateBranch(BriefcaseCommandError):
+    def __init__(self, template_repo, branch):
         super().__init__(
-            f"Could not find a template branch for Briefcase {briefcase_version}."
+            f"{branch} did not match any branches in template repository {template_repo}."
         )
 
 

tests/commands/base/test_update_cookiecutter_cache.py

@@ -5,7 +5,7 @@
 import pytest
 from git import exc as git_exceptions
 
-from briefcase.exceptions import BriefcaseCommandError, TemplateUnsupportedVersion
+from briefcase.exceptions import BriefcaseCommandError, InvalidTemplateBranch
 
 from ...utils import create_file
 
@@ -394,7 +394,7 @@ def test_cached_missing_branch_template(base_command, mock_git):
     cached_path.mkdir(parents=True)
 
     # Generating the template under there conditions raises an error
-    with pytest.raises(TemplateUnsupportedVersion):
+    with pytest.raises(InvalidTemplateBranch):
         base_command.update_cookiecutter_cache(
             template="https://example.com/magic/special-template.git",
             branch="invalid",

tests/commands/create/test_generate_app_template.py

@@ -12,8 +12,8 @@
 from briefcase.exceptions import (
     BriefcaseCommandError,
     BriefcaseConfigError,
+    InvalidTemplateBranch,
     NetworkFailure,
-    TemplateUnsupportedVersion,
 )
 
 
@@ -243,7 +243,7 @@ def test_default_template_dev_explicit_invalid_branch(
     )
 
     # Generate the template.
-    with pytest.raises(TemplateUnsupportedVersion):
+    with pytest.raises(InvalidTemplateBranch):
         create_command.generate_app_template(myapp)
 
     # Cookiecutter was invoked (once) with the expected template name and context.
@@ -651,7 +651,7 @@ def test_cached_missing_branch_template(monkeypatch, create_command, myapp):
     mock_remote.refs.__getitem__.side_effect = IndexError
 
     # Generating the template under there conditions raises an error
-    with pytest.raises(TemplateUnsupportedVersion):
+    with pytest.raises(InvalidTemplateBranch):
         create_command.generate_app_template(myapp)
 
 

tests/commands/new/test_new_app.py

@@ -10,8 +10,8 @@
 from briefcase.console import Console, Log
 from briefcase.exceptions import (
     BriefcaseCommandError,
+    InvalidTemplateBranch,
     InvalidTemplateRepository,
-    TemplateUnsupportedVersion,
 )
 
 
@@ -123,7 +123,7 @@ def test_new_app_missing_template(monkeypatch, new_command, tmp_path):
     )
 
     # Create the new app, using the default template. This raises an error.
-    with pytest.raises(TemplateUnsupportedVersion):
+    with pytest.raises(InvalidTemplateBranch):
         new_command.new_app()
 
     # App context is constructed
@@ -397,7 +397,7 @@ def test_new_app_with_invalid_template_branch(monkeypatch, new_command, tmp_path
     )
 
     # Create a new app, with a specific template; this raises an error
-    with pytest.raises(TemplateUnsupportedVersion):
+    with pytest.raises(InvalidTemplateBranch):
         new_command.new_app(template="https://example.com/other.git")
 
     # App context is constructed