chore: import upstream snapshot with attribution

tests/python/test_construct_chat_template_validation.py

@@ -0,0 +1,106 @@
+"""Negative-path validation tests for unsloth.chat_templates.construct_chat_template.
+
+Regression coverage for the no-match guards added in the PR #5763 follow-up:
+missing placeholders or unrecoverable two-example structures must raise
+RuntimeError with a clear message (not IndexError/AttributeError) and must
+not silently drop the last char via s[:-1]. A minimal fake tokenizer keeps
+the cases CPU-only (no HF_TOKEN, no gated download).
+"""
+
+from types import SimpleNamespace
+
+import pytest
+
+from unsloth.chat_templates import construct_chat_template
+
+
+class _FakeTokenizer:
+    """Minimal surface construct_chat_template touches before the guards fire."""
+
+    name_or_path = "fake/tokenizer"
+    eos_token = "</s>"
+
+    def get_vocab(self):
+        return {"</s>": 0}
+
+
+@pytest.mark.parametrize(
+    "template, expected_in_message",
+    [
+        ("only {INPUT} here, no output marker", "{OUTPUT}"),
+        ("only {OUTPUT} here, no input marker", "{INPUT}"),
+        ("neither sentinel here, just literal text", "{INPUT}"),
+        ("neither sentinel here, just literal text", "{OUTPUT}"),
+    ],
+)
+def test_missing_placeholder_in_chat_template_raises(template, expected_in_message):
+    with pytest.raises(RuntimeError) as exc_info:
+        construct_chat_template(
+            tokenizer = _FakeTokenizer(),
+            chat_template = template,
+            extra_eos_tokens = ["</s>"],
+        )
+    assert expected_in_message in str(exc_info.value)
+
+
+def test_single_pair_template_raises_clear_error_not_attribute_error():
+    """A single {INPUT}/{OUTPUT} pair must raise RuntimeError, not the old
+    AttributeError on `found.group(1)` when the loop broke without setting `found`."""
+    template = "user: {INPUT}\nassistant: {OUTPUT}\n"
+    with pytest.raises(RuntimeError):
+        construct_chat_template(
+            tokenizer = _FakeTokenizer(),
+            chat_template = template,
+            extra_eos_tokens = ["</s>"],
+        )
+
+
+def test_error_message_excerpt_is_bounded():
+    """Error messages must include a bounded excerpt of the offending
+    template, not dump arbitrarily large content into the traceback."""
+    huge = ("garbage " * 5000) + "{INPUT}"  # ~40 KB, missing {OUTPUT}
+    with pytest.raises(RuntimeError) as exc_info:
+        construct_chat_template(
+            tokenizer = _FakeTokenizer(),
+            chat_template = huge,
+            extra_eos_tokens = ["</s>"],
+        )
+    msg = str(exc_info.value)
+    # Excerpt is capped well under the template length.
+    assert len(msg) < 1000
+    assert "{OUTPUT}" in msg
+
+
+class _SuccessFakeTokenizer(_FakeTokenizer):
+    """Adds the surface construct_chat_template touches on the success path."""
+
+    bos_token = "<s>"
+    bos_token_id = 1
+    added_tokens_decoder: dict = {}
+
+    def __call__(self, text):
+        # input_ids[0] must differ from bos_token_id so the BOS-handling branch is skipped.
+        return SimpleNamespace(input_ids = [5])
+
+
+@pytest.mark.parametrize(
+    "chat_template",
+    [
+        # User turn begins with {INPUT} (no prefix before the sentinel).
+        "{INPUT} [/INST] {OUTPUT}</s>{INPUT} [/INST] {OUTPUT}</s>",
+        # Assistant turn begins with {OUTPUT} (no prefix before the sentinel).
+        "User: {INPUT}\n{OUTPUT}</s>User: {INPUT}\n{OUTPUT}</s>",
+    ],
+)
+def test_chat_template_does_not_leak_sentinel_when_section_starts_with_it(chat_template):
+    """When an input/output section begins with the {INPUT}/{OUTPUT} sentinel, the
+    generated Jinja template must not keep the literal sentinel text. The `startswith`
+    branch in the internal `process()` helper used to slice from `find()` (which is 0
+    here) instead of past the sentinel, re-including the literal `{INPUT}`/`{OUTPUT}`."""
+    _, jinja_template, _, _ = construct_chat_template(
+        tokenizer = _SuccessFakeTokenizer(),
+        chat_template = chat_template,
+        extra_eos_tokens = ["</s>"],
+    )
+    assert "{INPUT}" not in jinja_template
+    assert "{OUTPUT}" not in jinja_template