fix(fs): move FsBlockStore::list outside of async_trait

see comments in rs-ipfs#458. it is unknown why this is needed but it does work
away of the compiler error.

it was later found out by bisecting Cargo.lock that this is caused by
async-trait 0.1.42 => 0.1.43 upgrade, but it's very unclear why this
would be caused by the only PR in that release.

src/repo/fs/blocks.rs

@@ -355,46 +355,58 @@ impl BlockStore for FsBlockStore {
     }
 
     async fn list(&self) -> Result<Vec<Cid>, Error> {
-        use futures::future::{ready, Either};
-        use futures::stream::{empty, TryStreamExt};
-        use tokio_stream::wrappers::ReadDirStream;
-
-        let span = tracing::trace_span!("listing blocks");
-
-        async move {
-            let stream = ReadDirStream::new(fs::read_dir(self.path.clone()).await?);
-
-            // FIXME: written as a stream to make the Vec be BoxStream<'static, Cid>
-            let vec = stream
-                .and_then(|d| async move {
-                    // map over the shard directories
-                    Ok(if d.file_type().await?.is_dir() {
-                        Either::Left(ReadDirStream::new(fs::read_dir(d.path()).await?))
-                    } else {
-                        Either::Right(empty())
+        /// Implementation moved here from inside the `impl BlockStore for FsBlockStore` which is
+        /// `#[async_trait]`, and somehow the two lifetimes generated by `#[async_trait]` just don't
+        /// work leading to confusing error when `ipfs` is used as a dependency in an outside of
+        /// workspace crate.
+        ///
+        /// See [gist] for the standalone working workaround, error and an expanded version of the
+        /// original code.
+        ///
+        /// [gist]: https://gist.github.com/koivunej/d6abccb4133839eeab8b36992f1a95fa
+        async fn list0(p: PathBuf) -> Result<Vec<Cid>, Error> {
+            use futures::future::{ready, Either};
+            use futures::stream::{empty, TryStreamExt};
+            use tokio_stream::wrappers::ReadDirStream;
+
+            let span = tracing::trace_span!("listing blocks");
+
+            async move {
+                let stream = ReadDirStream::new(fs::read_dir(p).await?);
+
+                // FIXME: written as a stream to make the Vec be BoxStream<'static, Cid>
+                let vec = stream
+                    .and_then(|d| async move {
+                        // map over the shard directories
+                        Ok(if d.file_type().await?.is_dir() {
+                            Either::Left(ReadDirStream::new(fs::read_dir(d.path()).await?))
+                        } else {
+                            Either::Right(empty())
+                        })
                     })
-                })
-                // flatten each
-                .try_flatten()
-                // convert the paths ending in ".data" into cid
-                .try_filter_map(|d| {
-                    let name = d.file_name();
-                    let path: &std::path::Path = name.as_ref();
-
-                    ready(if path.extension() != Some("data".as_ref()) {
-                        Ok(None)
-                    } else {
-                        let maybe_cid = filestem_to_block_cid(path.file_stem());
-                        Ok(maybe_cid)
+                    // flatten each
+                    .try_flatten()
+                    // convert the paths ending in ".data" into cid
+                    .try_filter_map(|d| {
+                        let name = d.file_name();
+                        let path: &std::path::Path = name.as_ref();
+
+                        ready(if path.extension() != Some("data".as_ref()) {
+                            Ok(None)
+                        } else {
+                            let maybe_cid = filestem_to_block_cid(path.file_stem());
+                            Ok(maybe_cid)
+                        })
                     })
-                })
-                .try_collect::<Vec<_>>()
-                .await?;
+                    .try_collect::<Vec<_>>()
+                    .await?;
 
-            Ok(vec)
+                Ok(vec)
+            }
+            .instrument(span)
+            .await
         }
-        .instrument(span)
-        .await
+        list0(self.path.to_owned()).await
     }
 
     async fn wipe(&self) {