TemplateProcessing - Add @narsil suggestions

Co-authored-by: Nicolas Patry <patry.nicolas@protonmail.com>

bindings/python/py_src/tokenizers/processors/__init__.pyi

@@ -129,6 +129,11 @@ class TemplateProcessing(PostProcessor):
 
     Note that we are saying the "default" type_id because each SpecialToken can define
     its own type_id which would override the provided default.
+
+    **Warning**: You must ensure that you are giving the correct tokens/ids as these
+    will be added to the Encoding without any further check. If the given ids correspond
+    to something totally different in a `Tokenizer` using this `PostProcessor`, it
+    might lead to unexpected results.
     """
 
     def __init__(self, seq_a: Template, seq_b: Template, special_tokens: Tokens) -> None:

tokenizers/src/processors/template.rs

@@ -38,11 +38,17 @@
 //! Note that we are saying the "default" `type_id` because each `SpecialToken` can define
 //! its own `type_id` which would override the provided default.
 //!
+//! **Warning**: You must ensure that you are giving the correct tokens/ids as these will
+//! be added to the `Encoding` without any further check. If the given ids correspond to
+//! something totally different in a `Tokenizer` using this `PostProcessor`, it might lead
+//! to unexpected results.
+//!
 //! [`TemplateProcessing`]: struct.TemplateProcessing.html
 //!
 use crate::{Encoding, PostProcessor, Result};
+use itertools::Itertools;
 use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 /// Represents the different kind of pieces that constitute a template.
 /// It can be either the input sequence or a [`SpecialToken`]:
@@ -337,14 +343,15 @@ impl TemplateProcessingBuilder {
                 .special_tokens
                 .as_ref()
                 .map_or(false, |map| map.0.contains_key(sp));
+
             match exist {
-                true => Ok(()),
+                false => Some(sp),
-                false => Err(format!("The special token `{}` is missing", sp)),
+                true => None,
             }
         };
 
         let empty = vec![];
-        let seq = self
+        let missing: HashSet<&str> = self
             .sequence_a
             .as_ref()
             .map_or(empty.iter(), |s| s.0.iter())
@@ -352,16 +359,21 @@ impl TemplateProcessingBuilder {
                 self.sequence_b
                     .as_ref()
                     .map_or(empty.iter(), |s| s.0.iter()),
-            );
+            )
+            .filter_map(|piece| match piece {
+                Piece::Sequence { .. } => None,
+                Piece::SpecialToken { id } => check(id.as_ref()),
+            })
+            .collect::<HashSet<_>>();
 
-        for piece in seq {
+        if missing.is_empty() {
-            match piece {
+            Ok(())
-                Piece::Sequence { .. } => {}
+        } else {
-                Piece::SpecialToken { id } => check(id)?,
+            Err(format!(
-            }
+                "Missing SpecialToken(s) with id(s) `{}`",
+                missing.iter().join(", ")
+            ))
         }
-
-        Ok(())
     }
 }
 
@@ -402,7 +414,7 @@ impl TemplateProcessing {
                         self.special_tokens
                             .0
                             .get(id)
-                            .ok_or(format!("Missing SpecialToken with id {}", id))?
+                            .ok_or_else(|| format!("Missing SpecialToken with id {}", id))?
                             .ids
                             .len()
                     } else {
@@ -647,6 +659,18 @@ mod tests {
         );
     }
 
+    #[test]
+    fn missing_special_tokens() {
+        let processor = TemplateProcessing::builder()
+            .sequence_a("[CLS] $0 [SEP]")
+            .sequence_b("$1 [SEP]")
+            .build();
+
+        let err_a = Err("Missing SpecialToken(s) with id(s) `[SEP], [CLS]`".into());
+        let err_b = Err("Missing SpecialToken(s) with id(s) `[CLS], [SEP]`".into());
+        assert!(processor == err_a || processor == err_b);
+    }
+
     #[test]
     fn template_processing() {
         let processor = tests::get_bert_template();