fix(resolver): keep all candidates when all exceed max-release-age cutoff

Revert to keep-all-and-warn behavior when every candidate is older than
the max-release-age cutoff, instead of raising ResolverException. This
avoids empty resolution and lets the build proceed with a warning.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Rohan Devasthale <rdevasth@redhat.com>

Author: rd4398

src/fromager/resolver.py

@@ -237,15 +237,11 @@ def find_all_matching_from_provider(
         provider: The provider to query for candidates.
         req: The requirement to match.
         max_age_cutoff: If set, reject candidates published before this time.
-            Raises ``ResolverException`` if all candidates are older than
-            the cutoff.
+            If all candidates are older than the cutoff, all are kept and
+            a warning is emitted to avoid empty resolution.
 
     Returns list of (url, version) tuples sorted by version (highest first).
 
-    Raises:
-        ResolverException: If ``max_age_cutoff`` is set and every candidate
-            is older than the cutoff.
-
     IMPORTANT: This bypasses resolvelib's full resolver to collect all matching
     candidates. This is safe ONLY because BaseProvider.get_dependencies() returns
     an empty list (no transitive dependencies to resolve). The empty incompatibilities
@@ -301,12 +297,17 @@ def find_all_matching_from_provider(
                 req,
                 max_age_days,
             )
-        if not filtered:
-            raise resolvelib.resolvers.ResolverException(
-                f"all {len(candidates_list)} candidate(s) for {req} were "
-                f"published before the max-release-age cutoff"
+        if filtered:
+            candidates_list = filtered
+        else:
+            logger.warning(
+                "%s: all %d candidate(s) of %s are older than %d days, "
+                "keeping all to avoid empty resolution",
+                req.name,
+                len(candidates_list),
+                req,
+                max_age_days,
             )
-        candidates_list = filtered
 
     # Convert candidates to list of (url, version) tuples
     # Candidates are sorted by version (highest first) by BaseProvider.find_matches()

tests/test_cooldown.py

@@ -759,8 +759,10 @@ def test_max_release_age_disabled_returns_all() -> None:
     assert "1.2.2" in versions
 
 
-def test_max_release_age_all_too_old_raises() -> None:
-    """When all versions are older than cutoff, raise ResolverException."""
+def test_max_release_age_all_too_old_keeps_all(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """When all versions are older than cutoff, keep all candidates and warn."""
     max_age_cutoff = _BOOTSTRAP_TIME + datetime.timedelta(days=1)
     with requests_mock.Mocker() as r:
         r.get(
@@ -769,13 +771,13 @@ def test_max_release_age_all_too_old_raises() -> None:
             headers={"Content-Type": _PYPI_SIMPLE_JSON_CONTENT_TYPE},
         )
         provider = resolver.PyPIProvider(include_sdists=True)
-        with pytest.raises(
-            resolvelib.resolvers.ResolverException,
-            match=r"all 3 candidate.*max-release-age cutoff",
-        ):
-            resolver.find_all_matching_from_provider(
+        with caplog.at_level(logging.WARNING, logger="fromager.resolver"):
+            results = resolver.find_all_matching_from_provider(
                 provider, Requirement("test-pkg"), max_age_cutoff=max_age_cutoff
             )
+    versions = [str(v) for _, v in results]
+    assert versions == ["2.0.0", "1.3.2", "1.2.2"]
+    assert "keeping all to avoid empty resolution" in caplog.text
 
 
 def test_max_release_age_candidates_without_upload_time_pass_through() -> None: