PyTorchFileRecord print debug option (#1425)

* Add debug print option to PyTorchFileRecorder

* Updated documentation and improved print output

* Improve print wording

* Updated per PR feedback

burn-book/src/import/pytorch-model.md

@@ -230,8 +230,8 @@ Which produces the following weights structure (viewed in
 You can use the `PyTorchFileRecorder` to change the attribute names and the order of the attributes
 by specifying a regular expression (See
 [regex::Regex::replace](https://docs.rs/regex/latest/regex/struct.Regex.html#method.replace) and
-[try it online](https://rregex.dev/?version=1.10&method=replace)) to
-match the attribute name and a replacement string in `LoadArgs`:
+[try it online](https://rregex.dev/?version=1.10&method=replace)) to match the attribute name and a
+replacement string in `LoadArgs`:
 
 ```rust
 let device = Default::default();
@@ -246,6 +246,46 @@ let record = PyTorchFileRecorder::<FullPrecisionSettings>::default()
 let model = Net::<Backend>::new_with(record);
 ```
 
+### Printing the source model keys and tensor information
+
+If you are unsure about the keys in the source model, you can print them using the following code:
+
+```rust
+let device = Default::default();
+let load_args = LoadArgs::new("tests/key_remap/key_remap.pt".into())
+    // Remove "conv" prefix, e.g. "conv.conv1" -> "conv1"
+    .with_key_remap("conv\\.(.*)", "$1")
+    .with_debug_print(); // Print the keys and remapped keys
+
+let record = PyTorchFileRecorder::<FullPrecisionSettings>::default()
+    .load(load_args, &device)
+    .expect("Should decode state successfully");
+
+let model = Net::<Backend>::new_with(record);
+```
+
+Here is an example of the output:
+
+```text
+Debug information of keys and tensor shapes:
+---
+Original Key: conv.conv1.bias
+Remapped Key: conv1.bias
+Shape: [2]
+Dtype: F32
+---
+Original Key: conv.conv1.weight
+Remapped Key: conv1.weight
+Shape: [2, 2, 2, 2]
+Dtype: F32
+---
+Original Key: conv.conv2.weight
+Remapped Key: conv2.weight
+Shape: [2, 2, 2, 2]
+Dtype: F32
+---
+```
+
 ### Loading the model weights to a partial model
 
 `PyTorchFileRecorder` enables selective weight loading into partial models. For instance, in a model
@@ -254,11 +294,12 @@ defining the encoder in Burn, allowing the loading of its weights while excludin
 
 ### Specifying the top-level key for state_dict
 
-Sometimes the [`state_dict`](https://pytorch.org/tutorials/beginner/saving_loading_models.html#what-is-a-state-dict)
+Sometimes the
+[`state_dict`](https://pytorch.org/tutorials/beginner/saving_loading_models.html#what-is-a-state-dict)
 is nested under a top-level key along with other metadata as in a
 [general checkpoint](https://pytorch.org/tutorials/beginner/saving_loading_models.html#saving-loading-a-general-checkpoint-for-inference-and-or-resuming-training).
-For example, the `state_dict` of the whisper model is nested under `model_state_dict` key.
-In this case, you can specify the top-level key in `LoadArgs`:
+For example, the `state_dict` of the whisper model is nested under `model_state_dict` key. In this
+case, you can specify the top-level key in `LoadArgs`:
 
 ```rust
 let device = Default::default();

crates/burn-core/src/record/serde/data.rs

@@ -182,19 +182,25 @@ impl NestedValue {
 /// * `key_remap` - A vector of tuples containing a regular expression and a replacement string.
 ///                See [regex::Regex::replace](https://docs.rs/regex/latest/regex/struct.Regex.html#method.replace)
 ///                for more information.
-///
 /// # Returns
 ///
-/// A map of tensors with the remapped keys.
+/// A map of tensors with the remapped keys and
+/// a vector of tuples containing the remapped and original.
 pub fn remap<T>(
     mut tensors: HashMap<String, T>,
     key_remap: Vec<(Regex, String)>,
-) -> HashMap<String, T> {
+) -> (HashMap<String, T>, Vec<(String, String)>) {
     if key_remap.is_empty() {
-        return tensors;
+        let remapped_names = tensors
+            .keys()
+            .cloned()
+            .map(|s| (s.clone(), s)) // Name is the same as the remapped name
+            .collect();
+        return (tensors, remapped_names);
     }
 
     let mut remapped = HashMap::new();
+    let mut remapped_names = Vec::new();
 
     for (name, tensor) in tensors.drain() {
         let mut new_name = name.clone();
@@ -205,10 +211,12 @@ pub fn remap<T>(
                     .to_string();
             }
         }
+
+        remapped_names.push((new_name.clone(), name));
         remapped.insert(new_name, tensor);
     }
 
-    remapped
+    (remapped, remapped_names)
 }
 
 /// Helper function to insert a value into a nested map/vector of tensors.

crates/burn-import/pytorch-tests/tests/key_remap/mod.rs

@@ -41,7 +41,8 @@ mod tests {
     fn key_remap() {
         let device = Default::default();
         let load_args = LoadArgs::new("tests/key_remap/key_remap.pt".into())
-            .with_key_remap("conv\\.(.*)", "$1"); // Remove "conv" prefix, e.g. "conv.conv1" -> "conv1"
+            .with_key_remap("conv\\.(.*)", "$1") // Remove "conv" prefix, e.g. "conv.conv1" -> "conv1"
+            .with_debug_print();
 
         let record = PyTorchFileRecorder::<FullPrecisionSettings>::default()
             .load(load_args, &device)

crates/burn-import/src/pytorch/reader.rs

@@ -35,6 +35,7 @@ pub fn from_file<PS, D, B>(
     path: &Path,
     key_remap: Vec<(Regex, String)>,
     top_level_key: Option<&str>,
+    debug: bool,
 ) -> Result<D, Error>
 where
     D: DeserializeOwned,
@@ -48,7 +49,28 @@ where
         .collect();
 
     // Remap the keys (replace the keys in the map with the new keys)
-    let tensors = remap(tensors, key_remap);
+    let (tensors, remapped_keys) = remap(tensors, key_remap);
+
+    // Print the remapped keys if debug is enabled
+    if debug {
+        let mut remapped_keys = remapped_keys;
+        remapped_keys.sort();
+        println!("Debug information of keys and tensor shapes:\n---");
+        for (new_key, old_key) in remapped_keys {
+            if old_key != new_key {
+                println!("Original Key: {old_key}");
+                println!("Remapped Key: {new_key}");
+            } else {
+                println!("Key: {}", new_key);
+            }
+
+            let shape = tensors[&new_key].shape();
+            let dtype = tensors[&new_key].dtype();
+            println!("Shape: {shape:?}");
+            println!("Dtype: {dtype:?}");
+            println!("---");
+        }
+    }
 
     // Convert the vector of Candle tensors to a nested value data structure
     let nested_value = unflatten::<PS, _>(tensors)?;

crates/burn-import/src/pytorch/recorder.rs

@@ -48,6 +48,7 @@ impl<PS: PrecisionSettings, B: Backend> Recorder<B> for PyTorchFileRecorder<PS>
             &args.file,
             args.key_remap,
             args.top_level_key.as_deref(), // Convert Option<String> to Option<&str>
+            args.debug,
         )?;
         Ok(R::from_item(item, device))
     }
@@ -92,10 +93,13 @@ pub struct LoadArgs {
     /// Top-level key to load state_dict from the file.
     /// Sometimes the state_dict is nested under a top-level key in a dict.
     pub top_level_key: Option<String>,
+
+    /// Whether to print debug information.
+    pub debug: bool,
 }
 
 impl LoadArgs {
-    /// Create a new `LoadArgs` instance.
+    /// Creates a new `LoadArgs` instance.
     ///
     /// # Arguments
     ///
@@ -105,10 +109,11 @@ impl LoadArgs {
             file,
             key_remap: Vec::new(),
             top_level_key: None,
+            debug: false,
         }
     }
 
-    /// Set key remapping.
+    /// Sets key remapping.
     ///
     /// # Arguments
     ///
@@ -125,7 +130,7 @@ impl LoadArgs {
         self
     }
 
-    /// Set top-level key to load state_dict from the file.
+    /// Sets the top-level key to load state_dict from the file.
     /// Sometimes the state_dict is nested under a top-level key in a dict.
     ///
     /// # Arguments
@@ -135,6 +140,12 @@ impl LoadArgs {
         self.top_level_key = Some(key.into());
         self
     }
+
+    /// Sets printing debug information on.
+    pub fn with_debug_print(mut self) -> Self {
+        self.debug = true;
+        self
+    }
 }
 
 impl From<PathBuf> for LoadArgs {