Report error on multiple type builder blocks

engine/baml-lib/baml/tests/validation_files/tests/dynamic_types.baml

@@ -50,4 +50,4 @@ test ReturnDynamicClassTest {
       - Java
     "#
   }
-}
+}

engine/baml-lib/baml/tests/validation_files/tests/invalid_dynamic_types.baml

@@ -11,6 +11,30 @@ function ExtractResume(from_text: string) -> Resume {
   }
 }
 
+
+test ReturnDynamicClassTest {
+  functions [ExtractResume]
+  type_builder {
+    class Foo {
+      foo string
+    }
+    dynamic Bar {
+      bar int
+    }
+  }
+  type_builder {
+    class A {
+      a string
+    }
+    dynamic B {
+      b int
+    }
+  }
+  args {
+    from_text "Test"
+  }
+}
+
 // error: Error validating: Only tests may have a type_builder block.
 //   -->  tests/invalid_dynamic_types.baml:4
 //    | 
@@ -24,3 +48,16 @@ function ExtractResume(from_text: string) -> Resume {
 // 10 |     }
 // 11 |   }
 //    | 
+// error: Error validating: Definition of multiple `type_builder` blocks in the same parent block
+//   -->  tests/invalid_dynamic_types.baml:25
+//    | 
+// 24 |   }
+// 25 |   type_builder {
+// 26 |     class A {
+// 27 |       a string
+// 28 |     }
+// 29 |     dynamic B {
+// 30 |       b int
+// 31 |     }
+// 32 |   }
+//    | 

engine/baml-lib/schema-ast/src/parser/parse_value_expression_block.rs

@@ -88,7 +88,16 @@ pub(crate) fn parse_value_expression_block(
                         }
 
                         Rule::type_builder_block => {
-                            type_builder = Some(parse_type_builder_block(item, diagnostics)?);
+                            let block = parse_type_builder_block(item, diagnostics)?;
+
+                            match type_builder {
+                                None => type_builder = Some(block),
+
+                                Some(_) => diagnostics.push_error(DatamodelError::new_validation_error(
+                                    "Definition of multiple `type_builder` blocks in the same parent block",
+                                    block.span
+                                )),
+                            }
                         }
 
                         Rule::comment_block => pending_field_comment = Some(item),
@@ -140,10 +149,11 @@ pub(crate) fn parse_value_expression_block(
         ));
     };
 
-    // Only test blocks can have `type_builder` blocks in them.
+    // Only test blocks can have `type_builder` blocks in them. This is not a
+    // "syntax" error so we won't fail yet.
     if let Some(ref t) = type_builder {
         if sub_type != Some(ValueExprBlockType::Test) {
-            return Err(DatamodelError::new_validation_error(
+            diagnostics.push_error(DatamodelError::new_validation_error(
                 "Only tests may have a type_builder block.",
                 t.span.to_owned(),
             ));