PromptTemplate Validation fails on valid StTemplate Templates

[arlaneenalra]

Bug description
While attempting to pass complex objects as parameters to a PromptTemplate I discovered that the in built validation does not properly handle field references and likely other things that StTemplate natively supports.

Environment
Java Version: OpenJdk 17.0.16
Spring AI Version: 1.0.2

Steps to reproduce
With a complex test object like this:

class TestClass {
        private final String name;

        public TestClass(final String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }
}

And a unit like:

    @Test
    public void testPromptTemplate() {
        final PromptTemplate prompt = PromptTemplate.builder()
                .template("{test.name}")
                .build();
        final String result = prompt.render(Map.ofEntries(Map.entry("test", new TestClass("test"))));
        assertEquals("test", result);
    }

You get a failing test with a result like:

Not all variables were replaced in the template. Missing variable names are: [name].
java.lang.IllegalStateException: Not all variables were replaced in the template. Missing variable names are: [name].
	at org.springframework.ai.template.st.StTemplateRenderer.validate(StTemplateRenderer.java:140)
	at org.springframework.ai.template.st.StTemplateRenderer.apply(StTemplateRenderer.java:108)
	at org.springframework.ai.chat.prompt.PromptTemplate.render(PromptTemplate.java:137)

This seems to happen with any of the more advanced features of StTemplate.

Expected behavior
The test passes.

If you change the definition of the PromptTemplate call to:

        final PromptTemplate prompt = PromptTemplate.builder()
                .template("{test.name}")
                .renderer(StTemplateRenderer.builder()
                        .validationMode(ValidationMode.NONE)
                        .build())
                .build();

The test passes as expected.

Minimal Complete Reproducible example
See above.

[sunyuhan1998]

@arlaneenalra Thank you for your report. I've submitted a PR to address this issue—you can follow it here: #4499

[ilayaperumalg]

@sunyuhan1998 Thanks for the fix!