Validate tool args upfront with execute signature

Author: crmne

lib/ruby_llm/tool.rb

@@ -100,14 +100,13 @@ def params_schema
 
     def call(args)
       normalized_args = normalize_args(args)
+      validation_error = validate_keyword_arguments(normalized_args)
+      return { error: "Invalid tool arguments: #{validation_error}" } if validation_error
+
       RubyLLM.logger.debug { "Tool #{name} called with: #{normalized_args.inspect}" }
       result = execute(**normalized_args)
       RubyLLM.logger.debug { "Tool #{name} returned: #{result.inspect}" }
       result
-    rescue ArgumentError => e
-      raise e unless keyword_argument_error?(e)
-
-      { error: "Invalid tool arguments: #{e.message}" }
     end
 
     def execute(...)
@@ -127,9 +126,44 @@ def normalize_args(args)
       {}
     end
 
-    def keyword_argument_error?(error)
-      message = error.message.to_s
-      message.include?('unknown keyword') || message.include?('missing keyword')
+    def validate_keyword_arguments(arguments)
+      required_keywords, optional_keywords, accepts_extra_keywords = execute_keyword_signature
+
+      return nil if required_keywords.empty? && optional_keywords.empty?
+
+      argument_keys = arguments.keys
+      missing_keyword = first_missing_keyword(required_keywords, argument_keys)
+      return "missing keyword: #{keyword_label(missing_keyword)}" if missing_keyword
+      return nil if accepts_extra_keywords
+
+      allowed_keywords = required_keywords + optional_keywords
+      unknown_keyword = first_unknown_keyword(argument_keys, allowed_keywords)
+      return "unknown keyword: #{keyword_label(unknown_keyword)}" if unknown_keyword
+
+      nil
+    end
+
+    def execute_keyword_signature
+      keyword_signature = method(:execute).parameters
+      required_keywords = keyword_signature.filter_map { |kind, name| name if kind == :keyreq }
+      optional_keywords = keyword_signature.filter_map { |kind, name| name if kind == :key }
+      accepts_extra_keywords = keyword_signature.any? { |kind, _| kind == :keyrest }
+
+      [required_keywords, optional_keywords, accepts_extra_keywords]
+    end
+
+    def first_missing_keyword(required_keywords, argument_keys)
+      (required_keywords - argument_keys).first
+    end
+
+    def first_unknown_keyword(argument_keys, allowed_keywords)
+      (argument_keys - allowed_keywords).first
+    end
+
+    def keyword_label(keyword)
+      return keyword.to_s if RUBY_ENGINE == 'jruby'
+
+      ":#{keyword}"
     end
 
     # Wraps schema handling for tool parameters, supporting JSON Schema hashes,