add 'right' option for 'truncation_strategy'

docs/source/Instruction/命令行参数.md

@@ -45,7 +45,7 @@
 - 🔥template: 对话模板类型，默认使用model对应的template类型。`swift pt`会将对话模版转为生成模板使用
 - 🔥system: 自定义system字段，默认为None，使用template的默认system
 - 🔥max_length: 单样本的tokens最大长度，默认为None，不做限制
-- truncation_strategy: 如果超长如何处理，支持`delete`和`left`，代表删除和左侧裁剪，默认为'delete'
+- truncation_strategy: 如果超长如何处理，支持`delete`, `left`和`right`，代表删除、左侧裁剪和右侧裁剪，默认为'delete'
 - 🔥max_pixels: 多模态模型图片前处理的最大像素数（H\*W），默认不缩放。
 - tools_prompt: 智能体训练时的工具列表转为system的格式，请参考[智能体训练](./智能体的支持.md)，默认为'react_en'
 - loss_scale: 如何针对训练添加token的loss权重。默认为`'default'`，代表所有response（含history）以1计算交叉熵损失。具体可以查看[插件化](../Customization/插件化.md)和[智能体训练](./智能体的支持.md)

docs/source_en/Instruction/Command-line-parameters.md

@@ -45,7 +45,7 @@ The introduction to command line parameters will cover base arguments, atomic ar
 - 🔥template: Type of dialogue template, which defaults to the template type corresponding to the model. `swift pt` will convert the dialogue template into a generation template for use.
 - 🔥system: Custom system field, default is None, uses the default system of the template.
 - 🔥max_length: Maximum length of tokens for a single sample, default is None (no limit).
-- truncation_strategy: How to handle overly long tokens, supports `delete` and `left`, representing deletion and left trimming, default is 'delete'.
+- truncation_strategy: How to handle overly long tokens, supports `delete`, `left`, `right`, representing deletion, left trimming, and right trimming, default is 'delete'.
 - 🔥max_pixels: Maximum pixel count for pre-processing images in multimodal models (H*W), default is no scaling.
 - tools_prompt: The list of tools for agent training converted to system format, refer to [Agent Training](./Agent-support.md), default is 'react_en'.
 - loss_scale: How to add token loss weight during training. Default is `'default'`, meaning all responses (including history) are treated as 1 for cross-entropy loss. For specifics, see [Pluginization](../Customization/Pluginization.md) and [Agent Training](./Agent-support.md).

swift/llm/argument/base_args/template_args.py

@@ -31,7 +31,7 @@ class TemplateArguments:
     system: Optional[str] = None  # Override the default_system in the template.
     max_length: Optional[int] = None
 
-    truncation_strategy: Literal['delete', 'left'] = 'delete'
+    truncation_strategy: Literal['delete', 'left', 'right'] = 'delete'
     max_pixels: Optional[int] = None
     tools_prompt: str = 'react_en'  # Override the default_tools_prompt in the template.
     # train

swift/llm/template/base.py

@@ -56,7 +56,7 @@ def __init__(
             *,
             use_chat_template: bool = True,
             template_backend: Literal['swift', 'jinja'] = 'swift',
-            truncation_strategy: Literal['raise', 'left'] = 'raise',
+            truncation_strategy: Literal['raise', 'left', 'right'] = 'raise',
             max_pixels: Optional[int] = None,
             tools_prompt: Optional[str] = None,
             # only for train
@@ -630,11 +630,18 @@ def _encode(self, inputs: StdTemplateInputs) -> Dict[str, Any]:
             if self.truncation_strategy == 'raise' and len(input_ids) > self.max_length:
                 raise MaxLengthError(f'Current length of row({len(input_ids)}) is larger'
                                      f' than the max_length({self.max_length}).')
-            input_ids = input_ids[-self.max_length:]
-            if labels is not None:
-                labels = labels[-self.max_length:]
-            if loss_scale is not None:
-                loss_scale = loss_scale[-self.max_length:]
+            elif self.truncation_strategy == 'right':
+                input_ids = input_ids[:self.max_length]
+                if labels is not None:
+                    labels = labels[:self.max_length]
+                if loss_scale is not None:
+                    loss_scale = loss_scale[:self.max_length]
+            else:
+                input_ids = input_ids[-self.max_length:]
+                if labels is not None:
+                    labels = labels[-self.max_length:]
+                if loss_scale is not None:
+                    loss_scale = loss_scale[-self.max_length:]
 
         encoded['input_ids'] = input_ids
         encoded['labels'] = labels

swift/llm/template/register.py

@@ -24,7 +24,7 @@ def get_template(
         *,
         use_chat_template: bool = True,
         template_backend: Literal['swift', 'jinja'] = 'swift',
-        truncation_strategy: Literal['raise', 'left'] = 'raise',
+        truncation_strategy: Literal['raise', 'left', 'right'] = 'raise',
         max_pixels: Optional[int] = None,  # h * w
         tools_prompt: str = 'react_en',
         # train