Filter out yanked files (#413)

Implement two behaviors for yanked versions:

* During `pip-compile`, yanked versions are filtered out entirely, we
currently treat them is if they don't exist. This is leads to confusing
error messages because a version that does exist seems to have suddenly
disappeared.
* During `pip-sync`, we warn when we fetch a remote distribution and it
has been yanked. We currently don't warn on cached or installed
distributions that have been yanked.

crates/pypi-types/src/lib.rs

@@ -1,7 +1,7 @@
 pub use direct_url::{ArchiveInfo, DirectUrl, VcsInfo, VcsKind};
 pub use lenient_requirement::LenientVersionSpecifiers;
 pub use metadata::{Error, Metadata21};
-pub use simple_json::{File, SimpleJson};
+pub use simple_json::{File, SimpleJson, Yanked};
 
 mod direct_url;
 mod lenient_requirement;

crates/pypi-types/src/simple_json.rs

@@ -66,6 +66,15 @@ pub enum Yanked {
     Reason(String),
 }
 
+impl Yanked {
+    pub fn is_yanked(&self) -> bool {
+        match self {
+            Yanked::Bool(is_yanked) => *is_yanked,
+            Yanked::Reason(_) => true,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Hashes {
     pub sha256: String,