fix: Allow unknown timestamps in exclude-newer (#5848)

Author: pavelzw

crates/pixi/tests/integration_rust/build_tests.rs

@@ -732,18 +732,9 @@ bar = "{override_cutoff}"
     );
     pixi.update_manifest(&manifest_with_both_overrides).unwrap();
 
-    let err = pixi
-        .install()
+    pixi.install()
         .await
-        .expect_err("timestamp-less source package should remain the only blocker");
-    let rendered = format_diagnostic(err.as_ref());
-    assert!(
-        rendered.contains("my-package 1.0.0 is excluded"),
-        "{rendered}"
-    );
-    assert!(rendered.contains("package has no timestamp"), "{rendered}");
-    assert!(!rendered.contains("bar 1 is excluded"), "{rendered}");
-    assert!(!rendered.contains("foo 1 is excluded"), "{rendered}");
+        .expect("timestamp-less pixi-build source packages should remain eligible");
 }
 
 /// Test that demonstrates using PassthroughBackend with PixiControl

crates/pixi_spec/src/exclude_newer.rs

@@ -34,7 +34,6 @@ pub struct ResolvedExcludeNewer {
     pub package_cutoffs: BTreeMap<PackageName, DateTime<Utc>>,
 
     /// Whether to include packages that don't have a timestamp.
-    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub include_unknown_timestamp: bool,
 }
 
@@ -59,7 +58,9 @@ impl ResolvedExcludeNewer {
             cutoff,
             channel_cutoffs: BTreeMap::new(),
             package_cutoffs: BTreeMap::new(),
-            include_unknown_timestamp: false,
+            // TODO: After https://github.com/conda/ceps/pull/154 we might need to rethink this
+            // https://github.com/prefix-dev/pixi/pull/5848/changes#r3051252281
+            include_unknown_timestamp: true,
         }
     }
 
@@ -324,5 +325,6 @@ mod test {
             ),
             package_cutoff
         );
+        assert!(config.include_unknown_timestamp());
     }
 }