Allow setting a fallback version in case everything else fails.

7 files changed, 40 insertions, 6 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index f0b299d..4707051 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -1,3 +1,8 @@
+next
+====
+
+* fix #198 by adding the ``fallback_version`` option, which sets the version to be used when everything else fails.
+
 v3.2.0
 ======
 
diff --git a/README.rst b/README.rst
index 099add8..9f6f105 100644
--- a/README.rst
+++ b/README.rst
@@ -253,12 +253,6 @@ The currently supported configuration keys are:
     repository to point ``setuptools_scm`` at the root of the repository by
     supplying ``__file__``.
 
-:parse:
-    A function that will be used instead of the discovered SCM for parsing the
-    version.
-    Use with caution, this is a function for advanced use, and you should be
-    familiar with the ``setuptools_scm`` internals to use it.
-
 :tag_regex:
     A Python regex string to extract the version part from any SCM tag.
     The regex needs to contain three named groups prefix, version and suffix,
@@ -267,6 +261,18 @@ The currently supported configuration keys are:
     Defaults to the value of ``setuptools_scm.config.DEFAULT_TAG_REGEX``
     (see `config.py <src/setuptools_scm/config.py>`_).
 
+:fallback_version:
+    A version string that will be used if no other method for detecting the
+    version worked (e.g., when using a tarball with no metadata).  If this is
+    unset (the default), setuptools_scm will error if it fails to detect the
+    version.
+
+:parse:
+    A function that will be used instead of the discovered SCM for parsing the
+    version.
+    Use with caution, this is a function for advanced use, and you should be
+    familiar with the ``setuptools_scm`` internals to use it.
+
 :git_describe_command:
     This command will be used instead the default ``git describe`` command.
     Use with caution, this is a function for advanced use, and you should be
diff --git a/setup.py b/setup.py
index 6981232..2eb533b 100644
--- a/setup.py
+++ b/setup.py
@@ -76,6 +76,7 @@ arguments = dict(
         .hg_archival.txt = setuptools_scm.hg:parse_archival
         PKG-INFO = setuptools_scm.hacks:parse_pkginfo
         pip-egg-info = setuptools_scm.hacks:parse_pip_egg_info
+        setup.py = setuptools_scm.hacks:fallback_version
 
         [setuptools_scm.files_command]
         .hg = setuptools_scm.file_finder_hg:hg_find_files
diff --git a/src/setuptools_scm/__init__.py b/src/setuptools_scm/__init__.py
index f49cce4..f9ab5c2 100644
--- a/src/setuptools_scm/__init__.py
+++ b/src/setuptools_scm/__init__.py
@@ -120,6 +120,7 @@ def get_version(
     write_to_template=None,
     relative_to=None,
     tag_regex=None,
+    fallback_version=None,
     parse=None,
     git_describe_command=None,
 ):
@@ -138,6 +139,7 @@ def get_version(
     config.write_to_template = write_to_template
     config.relative_to = relative_to
     config.tag_regex = tag_regex
+    config.fallback_version = fallback_version
     config.parse = parse
     config.git_describe_command = git_describe_command
 
diff --git a/src/setuptools_scm/config.py b/src/setuptools_scm/config.py
index 796dd0b..7b1d88b 100644
--- a/src/setuptools_scm/config.py
+++ b/src/setuptools_scm/config.py
@@ -44,6 +44,7 @@ class Configuration(object):
     local_scheme = None
     write_to = None
     write_to_template = None
+    fallback_version = None
     _relative_to = None
     parse = None
     _tag_regex = None
@@ -59,6 +60,7 @@ class Configuration(object):
         self.local_scheme = "node-and-date"
         self.write_to = ""
         self.write_to_template = None
+        self.fallback_version = None
         self.parse = None
         self.tag_regex = DEFAULT_TAG_REGEX
         self.git_describe_command = None
diff --git a/src/setuptools_scm/hacks.py b/src/setuptools_scm/hacks.py
index a4ca586..1ef0bb4 100644
--- a/src/setuptools_scm/hacks.py
+++ b/src/setuptools_scm/hacks.py
@@ -22,3 +22,8 @@ def parse_pip_egg_info(root, config=None):
     if not items:
         return
     return parse_pkginfo(os.path.join(pipdir, items[0]), config=config)
+
+
+def fallback_version(root, config=None):
+    if config.fallback_version is not None:
+        return meta(config.fallback_version, preformatted=True, config=config)
diff --git a/testing/test_basic_api.py b/testing/test_basic_api.py
index c032d23..5b5c6d6 100644
--- a/testing/test_basic_api.py
+++ b/testing/test_basic_api.py
@@ -1,4 +1,5 @@
 import os
+import sys
 import py
 import pytest
 
@@ -56,6 +57,18 @@ def test_root_parameter_pass_by(monkeypatch, tmpdir):
     setuptools_scm.get_version(root=tmpdir.strpath)
 
 
+def test_fallback(tmpdir, monkeypatch):
+    monkeypatch.delenv("SETUPTOOLS_SCM_DEBUG")
+    p = tmpdir.ensure("sub/package", dir=1)
+    p.join("setup.py").write(
+        """from setuptools import setup
+setup(use_scm_version={"fallback_version": "12.34"})
+"""
+    )
+    res = do((sys.executable, "setup.py", "--version"), p)
+    assert res == "12.34"
+
+
 @pytest.mark.parametrize(
     "version", ["1.0", "1.2.3.dev1+ge871260", "1.2.3.dev15+ge871260.d20180625", "2345"]
 )