internal: make sure that proc macro machinery doesn't depend on cwd

crates/paths/src/lib.rs

@@ -66,6 +66,27 @@ impl PartialEq<AbsPath> for AbsPathBuf {
     }
 }
 
+impl serde::Serialize for AbsPathBuf {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
+impl<'de> serde::Deserialize<'de> for AbsPathBuf {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        let path = PathBuf::deserialize(deserializer)?;
+        AbsPathBuf::try_from(path).map_err(|path| {
+            serde::de::Error::custom(format!("expected absolute path, got {}", path.display()))
+        })
+    }
+}
+
 impl AbsPathBuf {
     /// Wrap the given absolute path in `AbsPathBuf`
     ///