Include placeholder value for all secrets, not just kwargs (#6421)

Mirror PR for https://github.com/hwchase17/langchainjs/pull/1696

Secrets passed via environment variables should be present in the
serialised chain

tests/unit_tests/load/__snapshots__/test_dump.ambr

@@ -129,7 +129,13 @@
         "kwargs": {
           "model": "davinci",
           "temperature": 0.5,
-          "openai_api_key": "hello"
+          "openai_api_key": {
+            "lc": 1,
+            "type": "secret",
+            "id": [
+              "OPENAI_API_KEY"
+            ]
+          }
         }
       },
       "prompt": {

tests/unit_tests/load/test_dump.py

@@ -80,6 +80,28 @@ def test_serialize_llmchain(snapshot: Any) -> None:
     assert dumps(chain, pretty=True) == snapshot
 
 
+@pytest.mark.requires("openai")
+def test_serialize_llmchain_env() -> None:
+    llm = OpenAI(model="davinci", temperature=0.5, openai_api_key="hello")
+    prompt = PromptTemplate.from_template("hello {name}!")
+    chain = LLMChain(llm=llm, prompt=prompt)
+
+    import os
+
+    has_env = "OPENAI_API_KEY" in os.environ
+    if not has_env:
+        os.environ["OPENAI_API_KEY"] = "env_variable"
+
+    llm_2 = OpenAI(model="davinci", temperature=0.5)
+    prompt_2 = PromptTemplate.from_template("hello {name}!")
+    chain_2 = LLMChain(llm=llm_2, prompt=prompt_2)
+
+    assert dumps(chain_2, pretty=True) == dumps(chain, pretty=True)
+
+    if not has_env:
+        del os.environ["OPENAI_API_KEY"]
+
+
 @pytest.mark.requires("openai")
 def test_serialize_llmchain_chat(snapshot: Any) -> None:
     llm = ChatOpenAI(model="davinci", temperature=0.5, openai_api_key="hello")
@@ -89,6 +111,23 @@ def test_serialize_llmchain_chat(snapshot: Any) -> None:
     chain = LLMChain(llm=llm, prompt=prompt)
     assert dumps(chain, pretty=True) == snapshot
 
+    import os
+
+    has_env = "OPENAI_API_KEY" in os.environ
+    if not has_env:
+        os.environ["OPENAI_API_KEY"] = "env_variable"
+
+    llm_2 = ChatOpenAI(model="davinci", temperature=0.5)
+    prompt_2 = ChatPromptTemplate.from_messages(
+        [HumanMessagePromptTemplate.from_template("hello {name}!")]
+    )
+    chain_2 = LLMChain(llm=llm_2, prompt=prompt_2)
+
+    assert dumps(chain_2, pretty=True) == dumps(chain, pretty=True)
+
+    if not has_env:
+        del os.environ["OPENAI_API_KEY"]
+
 
 @pytest.mark.requires("openai")
 def test_serialize_llmchain_with_non_serializable_arg(snapshot: Any) -> None:

tests/unit_tests/load/test_load.py

@@ -39,6 +39,30 @@ def test_load_llmchain() -> None:
     assert isinstance(chain2.prompt, PromptTemplate)
 
 
+@pytest.mark.requires("openai")
+def test_load_llmchain_env() -> None:
+    import os
+
+    has_env = "OPENAI_API_KEY" in os.environ
+    if not has_env:
+        os.environ["OPENAI_API_KEY"] = "env_variable"
+
+    llm = OpenAI(model="davinci", temperature=0.5)
+    prompt = PromptTemplate.from_template("hello {name}!")
+    chain = LLMChain(llm=llm, prompt=prompt)
+    chain_string = dumps(chain)
+    chain2 = loads(chain_string)
+
+    assert chain2 == chain
+    assert dumps(chain2) == chain_string
+    assert isinstance(chain2, LLMChain)
+    assert isinstance(chain2.llm, OpenAI)
+    assert isinstance(chain2.prompt, PromptTemplate)
+
+    if not has_env:
+        del os.environ["OPENAI_API_KEY"]
+
+
 @pytest.mark.requires("openai")
 def test_load_llmchain_with_non_serializable_arg() -> None:
     llm = OpenAI(