PromptTemplate validation prevents the use of StringTemplate built-in functions

[asw12]

Bug description
PromptTemplate has a validate method that compares input variables used in the template (pulled straight from the underlying Antlr TokenStream) to the parameters provided in an attempt to verify that there are no unbound variables. However, StringTemplate has some built-in functions, and this validation is preventing their use.

Environment
Spring AI 1.0.0-M6
Java 17

Steps to reproduce
I was attempting to make it so that the prompt added by VectorStoreChatMemoryAdvisor would be added conditionally on whether there was actually data pulled from the chat history. Something like:

   String chatMemoryPrompt = """
                {if(strlen(long_term_memory))}

                Use the long term conversation memory from the LONG_TERM_MEMORY section to provide accurate answers.

                ---------------------
                LONG_TERM_MEMORY:
                {long_term_memory}
                ---------------------
                {endif}
                """;

    VectorStoreChatMemoryAdvisor.builder(chatHistoryStore)
                    .systemTextAdvise(chatMemoryPrompt)
                    .build();

But the validation considers strlen to be a variable that is unbound, and fails.

Expected behavior
I think the same conclusion from this can be reached as #1428 - make the validation optional.
But if we wanted to continue the validation "whack-a-mole", there exists a org.stringtemplate.v4.compiler.Compiler#funcs static map whose keys could be used to find the names of these built-in functions, and omit these in validation.
https://github.com/antlr/stringtemplate4/blob/master/src/org/stringtemplate/v4/compiler/Compiler.java#L81

[sunyuhan1998]

I submitted a PR to fix this issue: #2458

[markpollack]

Hi. @sunyuhan1998 thanks so much. I'm thinking to disable validation by default, I really haven't experienced cases where someone didn't replace the template values and was happy to have eager failure. Thoughts?

[sunyuhan1998]

Hi. @sunyuhan1998 thanks so much. I'm thinking to disable validation by default, I really haven't experienced cases where someone didn't replace the template values and was happy to have eager failure. Thoughts?

I think this kind of validation is mainly used to prevent users from forgetting to replace a certain variable in the template, which could lead to unexpected behavior when actually interacting with the model. Considering such scenarios, I believe the choice should be handed over to the users, as we discussed in the PR(#2458). By default, the validation should be disabled, and users should be allowed to specify it themselves in the constructor. This might be a good idea. I have already updated the PR, so please review it when you have time.

[markpollack]

I believe this commit 0e15197 address the situation best we can. Note, with nested calls to functions using property syntax the upfront validation gets very difficult to implement.

closing. thanks for all the feedback and help.