Push wheel timestamps to 1980 if SOURCE_DATE_EPOCH before that

flit_core/flit_core/tests/test_wheel.py

@@ -1,4 +1,5 @@
 from pathlib import Path
+from zipfile import ZipFile
 
 from testpath import assert_isfile
 
@@ -10,3 +11,11 @@ def test_licenses_dir(tmp_path):
     # Smoketest for https://github.com/takluyver/flit/issues/399
     info = make_wheel_in(samples_dir / 'inclusion' / 'pyproject.toml', tmp_path)
     assert_isfile(info.file)
+
+def test_zero_timestamp(tmp_path, monkeypatch):
+    monkeypatch.setenv('SOURCE_DATE_EPOCH', '0')
+    info = make_wheel_in(samples_dir / 'pep621' / 'pyproject.toml', tmp_path)
+    assert_isfile(info.file)
+    # Minimum value for zip timestamps is 1980-1-1
+    with ZipFile(info.file, 'r') as zf:
+        assert zf.getinfo('module1a.py').date_time == (1980, 1, 1, 0, 0, 0)

flit_core/flit_core/wheel.py

@@ -50,13 +50,19 @@ def __init__(self, directory, module, metadata, entrypoints, target_fp):
             # If SOURCE_DATE_EPOCH is set (e.g. by Debian), it's used for
             # timestamps inside the zip file.
             d = datetime.utcfromtimestamp(int(os.environ['SOURCE_DATE_EPOCH']))
-            log.info("Zip timestamps will be from SOURCE_DATE_EPOCH: %s", d)
-            # zipfile expects a 6-tuple, not a datetime object
-            self.source_time_stamp = (d.year, d.month, d.day, d.hour, d.minute, d.second)
         except (KeyError, ValueError):
             # Otherwise, we'll use the mtime of files, and generated files will
             # default to 2016-1-1 00:00:00
             self.source_time_stamp = None
+        else:
+            if d.year >= 1980:
+                log.info("Zip timestamps will be from SOURCE_DATE_EPOCH: %s", d)
+                # zipfile expects a 6-tuple, not a datetime object
+                self.source_time_stamp = (d.year, d.month, d.day, d.hour, d.minute, d.second)
+            else:
+                log.info("SOURCE_DATE_EPOCH is below the minimum for zip file timestamps")
+                log.info("Zip timestamps will be 1980-01-01 00:00:00")
+                self.source_time_stamp = (1980, 1, 1, 0, 0, 0)
 
         # Open the zip file ready to write
         self.wheel_zip = zipfile.ZipFile(target_fp, 'w',