DataLoaders 4: add generic folder DataLoader (#4520)

Load folders filled with whatever. Go nuts.

The loader has no particular semantics (e.g. HIVE partitioning): it just
loads everything in a folder using the appropriate loader(s) for each
file.

Checks:
- [x] `cargo r -p rerun-cli --no-default-features --features
native_viewer -- examples/assets`
- [x] Native: `File > Open > examples/assets/`
- [x] Native: `Drag-n-drop > examples/assets/`

---

Part of a series of PRs to make it possible to load _any_ file from the
local filesystem, by any means, on web and native:
- #4516
- #4517 
- #4518 
- #4519 
- #4520 
- #4521 
- TODO: register custom loaders
- TODO: high level docs and guides for everything related to loading
files

crates/re_data_source/src/data_loader/loader_directory.rs

@@ -0,0 +1,79 @@
+/// Recursively oads entire directories, using the appropriate [`crate::DataLoader`]:s for each
+/// files within.
+//
+// TODO(cmc): There are a lot more things than can be done be done when it comes to the semantics
+// of a folder, e.g.: HIVE-like partitioning, similarly named files with different indices and/or
+// timestamps (e.g. a folder of video frames), etc.
+// We could support some of those at some point, or at least add examples to show users how.
+pub struct DirectoryLoader;
+
+impl crate::DataLoader for DirectoryLoader {
+    #[inline]
+    fn name(&self) -> String {
+        "rerun.data_loaders.Directory".into()
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    fn load_from_path(
+        &self,
+        store_id: re_log_types::StoreId,
+        dirpath: std::path::PathBuf,
+        tx: std::sync::mpsc::Sender<crate::LoadedData>,
+    ) -> Result<(), crate::DataLoaderError> {
+        if dirpath.is_file() {
+            return Ok(()); // simply not interested
+        }
+
+        re_tracing::profile_function!(dirpath.display().to_string());
+
+        re_log::debug!(?dirpath, loader = self.name(), "Loading directory…",);
+
+        for entry in walkdir::WalkDir::new(&dirpath) {
+            let entry = match entry {
+                Ok(entry) => entry,
+                Err(err) => {
+                    re_log::error!(loader = self.name(), ?dirpath, %err, "Failed to open filesystem entry");
+                    continue;
+                }
+            };
+
+            let filepath = entry.path();
+            if filepath.is_file() {
+                let store_id = store_id.clone();
+                let filepath = filepath.to_owned();
+                let tx = tx.clone();
+
+                // NOTE: spawn is fine, this whole function is native-only.
+                rayon::spawn(move || {
+                    let data = match crate::load_file::load(&store_id, &filepath, false, None) {
+                        Ok(data) => data,
+                        Err(err) => {
+                            re_log::error!(?filepath, %err, "Failed to load directory entry");
+                            return;
+                        }
+                    };
+
+                    for datum in data {
+                        if tx.send(datum).is_err() {
+                            break;
+                        }
+                    }
+                });
+            }
+        }
+
+        Ok(())
+    }
+
+    #[inline]
+    fn load_from_file_contents(
+        &self,
+        _store_id: re_log_types::StoreId,
+        _path: std::path::PathBuf,
+        _contents: std::borrow::Cow<'_, [u8]>,
+        _tx: std::sync::mpsc::Sender<crate::LoadedData>,
+    ) -> Result<(), crate::DataLoaderError> {
+        // TODO(cmc): This could make sense to implement for e.g. archive formats (zip, tar, …)
+        Ok(()) // simply not interested
+    }
+}

crates/re_data_source/src/data_loader/mod.rs

@@ -205,6 +205,7 @@ static BUILTIN_LOADERS: Lazy<Vec<Arc<dyn DataLoader>>> = Lazy::new(|| {
     vec![
         Arc::new(RrdLoader) as Arc<dyn DataLoader>,
         Arc::new(ArchetypeLoader),
+        Arc::new(DirectoryLoader),
     ]
 });
 
@@ -217,7 +218,9 @@ pub fn iter_loaders() -> impl ExactSizeIterator<Item = Arc<dyn DataLoader>> {
 // ---
 
 mod loader_archetype;
+mod loader_directory;
 mod loader_rrd;
 
 pub use self::loader_archetype::ArchetypeLoader;
+pub use self::loader_directory::DirectoryLoader;
 pub use self::loader_rrd::RrdLoader;

crates/re_data_source/src/load_file.rs

@@ -98,11 +98,11 @@ pub fn extension(path: &std::path::Path) -> String {
 /// This does _not_ access the filesystem.
 #[inline]
 pub fn is_associated_with_builtin_loader(path: &std::path::Path, is_dir: bool) -> bool {
-    !is_dir && crate::is_supported_file_extension(&extension(path))
+    is_dir || crate::is_supported_file_extension(&extension(path))
 }
 
 /// Prepares an adequate [`re_log_types::StoreInfo`] [`LogMsg`] given the input.
-fn prepare_store_info(
+pub(crate) fn prepare_store_info(
     store_id: &re_log_types::StoreId,
     file_source: FileSource,
     path: &std::path::Path,
@@ -139,7 +139,7 @@ fn prepare_store_info(
 /// - On native, this is filled asynchronously from other threads.
 /// - On wasm, this is pre-filled synchronously.
 #[cfg_attr(target_arch = "wasm32", allow(clippy::needless_pass_by_value))]
-fn load(
+pub(crate) fn load(
     store_id: &re_log_types::StoreId,
     path: &std::path::Path,
     is_dir: bool,
@@ -218,7 +218,7 @@ fn load(
 /// Forwards the data in `rx_loader` to `tx`, taking care of necessary conversions, if any.
 ///
 /// Runs asynchronously from another thread on native, synchronously on wasm.
-fn send(
+pub(crate) fn send(
     store_id: &re_log_types::StoreId,
     rx_loader: std::sync::mpsc::Receiver<LoadedData>,
     tx: &Sender<LogMsg>,