[Rust Frontend] Fix macro-based content format detection (#49042)

Signed-off-by: reidliu41 <reid201711@gmail.com>

rust/src/chat/src/renderer/hf/format.rs

@@ -236,9 +236,10 @@ fn has_content_item_loop(root: &Stmt<'_>) -> bool {
 
     loops.into_iter().any(|loop_ast| {
         matches!(loop_ast.target, Expr::Var(_))
-            && message_varnames
-                .iter()
-                .any(|varname| is_var_or_elems_access(&loop_ast.iter, varname, Some("content")))
+            && (is_var_access(&loop_ast.iter, "content")
+                || message_varnames.iter().any(|varname| {
+                    is_var_or_elems_access(&loop_ast.iter, varname, Some("content"))
+                }))
     })
 }
 
@@ -315,6 +316,16 @@ mod tests {
         );
     }
 
+    #[test]
+    fn detects_openai_template_with_content_parameter_loop() {
+        assert_eq!(
+            detect(
+                "{% macro render(content) %}{% for item in content %}{{ item }}{% endfor %}{% endmacro %}{% for message in messages %}{{ render(message.content) }}{% endfor %}"
+            ),
+            ChatTemplateContentFormat::OpenAi
+        );
+    }
+
     #[test]
     fn detects_openai_template_with_messages_alias() {
         assert_eq!(

rust/src/chat/src/renderer/hf/mod.rs

@@ -1309,6 +1309,26 @@ mod tests {
         .assert_eq(&rendered);
     }
 
+    #[test]
+    fn qwen35_template_auto_detects_openai_multimodal_content() {
+        let mut request = image_request();
+        request.chat_options.generation_prompt_mode = GenerationPromptMode::NoGenerationPrompt;
+
+        let rendered = render_mm(
+            QWEN3_5_0_8B_TEMPLATE,
+            &request,
+            ChatTemplateContentFormatOption::Auto,
+        )
+        .unwrap();
+
+        expect![[r#"
+            Text(
+                "<|im_start|>user\na<|vision_start|><|image_pad|><|vision_end|>b<|im_end|>\n",
+            )
+        "#]]
+        .assert_debug_eq(&rendered.prompt);
+    }
+
     #[test]
     fn qwen35_template_renders_closed_empty_reasoning_span_when_thinking_disabled() {
         let mut request = sample_request(vec![ChatMessage::text(ChatRole::User, "hello")]);