chroma[patch]: fix bug (#28538)

Fix bug introduced in
https://github.com/langchain-ai/langchain/pull/27995

If all document IDs are `""`, the chroma SDK will raise
```
DuplicateIDError: Expected IDs to be unique
```

Caught by [docs
tests](https://github.com/langchain-ai/langchain/actions/runs/12180395579/job/33974633950),
but added a test to langchain-chroma as well.

libs/partners/chroma/langchain_chroma/vectorstores.py

@@ -1228,7 +1228,7 @@ class Chroma(VectorStore):
         texts = [doc.page_content for doc in documents]
         metadatas = [doc.metadata for doc in documents]
         if ids is None:
-            ids = [doc.id if doc.id else "" for doc in documents]
+            ids = [doc.id if doc.id else str(uuid.uuid4()) for doc in documents]
         return cls.from_texts(
             texts=texts,
             embedding=embedding,

libs/partners/chroma/tests/integration_tests/test_vectorstores.py

@@ -51,6 +51,22 @@ def test_chroma() -> None:
     assert output[0].id is not None
 
 
+def test_from_documents() -> None:
+    """Test init using .from_documents."""
+    documents = [
+        Document(page_content="foo"),
+        Document(page_content="bar"),
+        Document(page_content="baz"),
+    ]
+    docsearch = Chroma.from_documents(documents=documents, embedding=FakeEmbeddings())
+    output = docsearch.similarity_search("foo", k=1)
+
+    docsearch.delete_collection()
+    assert len(output) == 1
+    assert output[0].page_content == "foo"
+    assert output[0].id is not None
+
+
 def test_chroma_with_ids() -> None:
     """Test end to end construction and search."""
     texts = ["foo", "bar", "baz"]