update prompt variables to list for validation

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

llama_stack/apis/prompts/prompts.py

@@ -4,10 +4,11 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+import re
 import secrets
 from typing import Protocol, runtime_checkable
 
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field, field_validator, model_validator
 
 from llama_stack.providers.utils.telemetry.trace_protocol import trace_protocol
 from llama_stack.schema_utils import json_schema_type, webmethod
@@ -27,8 +28,8 @@ class Prompt(BaseModel):
     prompt: str | None = Field(default=None, description="The system prompt with variable placeholders")
     version: str = Field(description="Version string (integer start at 1 cast as string)")
     prompt_id: str = Field(description="Unique identifier in format 'pmpt_<48-digit-hash>'")
-    variables: dict[str, str] | None = Field(
-        default_factory=dict, description="Variables for dynamic injection using {{variable}} syntax"
+    variables: list[str] = Field(
+        default_factory=list, description="List of variable names that can be used in the prompt template"
     )
     is_default: bool = Field(
         default=False, description="Boolean indicating whether this version is the default version"
@@ -66,6 +67,21 @@ class Prompt(BaseModel):
             raise
         return prompt_version
 
+    @model_validator(mode="after")
+    def validate_prompt_variables(self):
+        """Validate that all variables used in the prompt are declared in the variables list."""
+        if not self.prompt:
+            return self
+
+        prompt_variables = set(re.findall(r"{{\s*(\w+)\s*}}", self.prompt))
+        declared_variables = set(self.variables)
+
+        undeclared = prompt_variables - declared_variables
+        if undeclared:
+            raise ValueError(f"Prompt contains undeclared variables: {sorted(undeclared)}")
+
+        return self
+
     @classmethod
     def generate_prompt_id(cls) -> str:
         # Generate 48 hex characters (24 bytes)
@@ -78,14 +94,14 @@ class CreatePromptRequest(BaseModel):
     """Request model to create a prompt."""
 
     prompt: str = Field(description="The prompt text content")
-    variables: dict[str, str] = Field(default_factory=dict, description="Variables for dynamic injection")
+    variables: list[str] = Field(default_factory=list, description="List of variable names for dynamic injection")
 
 
 class UpdatePromptRequest(BaseModel):
     """Request model for updating a prompt."""
 
     prompt: str = Field(description="The prompt text content")
-    variables: dict[str, str] = Field(default_factory=dict, description="Variables for dynamic injection")
+    variables: list[str] = Field(default_factory=list, description="List of variable names for dynamic injection")
 
 
 class ListPromptsResponse(BaseModel):
@@ -137,12 +153,12 @@ class Prompts(Protocol):
     async def create_prompt(
         self,
         prompt: str,
-        variables: dict[str, str] | None = None,
+        variables: list[str] | None = None,
     ) -> Prompt:
         """Create a new prompt.
 
         :param prompt: The prompt text content with variable placeholders.
-        :param variables: Dictionary of variable names to their default values.
+        :param variables: List of variable names that can be used in the prompt template.
         :returns: The created Prompt resource.
         """
         ...
@@ -152,14 +168,14 @@ class Prompts(Protocol):
         self,
         prompt_id: str,
         prompt: str,
-        variables: dict[str, str] | None = None,
+        variables: list[str] | None = None,
         version: str | None = None,
     ) -> Prompt:
         """Update an existing prompt (increments version).
 
         :param prompt_id: The identifier of the prompt to update.
         :param prompt: The updated prompt text content.
-        :param variables: Updated dictionary of variable names to their default values.
+        :param variables: Updated list of variable names that can be used in the prompt template.
         :param version: The current version of the prompt being updated (as a string).
         :returns: The updated Prompt resource with incremented version.
         """