[router][grpc] Refactor chat template content format detection (#11288)

sgl-router/src/tokenizer/chat_template.rs

@@ -4,7 +4,8 @@
 //! similar to HuggingFace transformers' apply_chat_template method.
 
 use anyhow::{anyhow, Result};
-use minijinja::{context, machinery, Environment, Value};
+use minijinja::machinery::ast::{Expr, Stmt};
+use minijinja::{context, Environment, Value};
 use serde_json;
 use std::collections::HashMap;
 
@@ -50,243 +51,293 @@ pub fn detect_chat_template_content_format(template: &str) -> ChatTemplateConten
     ChatTemplateContentFormat::String
 }
 
-/// AST-based detection using minijinja's unstable machinery
-/// This implements the exact same logic as SGLang's _is_var_or_elems_access functions
-fn detect_format_with_ast(template: &str) -> Option<ChatTemplateContentFormat> {
-    use minijinja::machinery::{parse, WhitespaceConfig};
-    use minijinja::syntax::SyntaxConfig;
+/// Flags tracking which OpenAI-style patterns we've seen
+#[derive(Default, Debug, Clone, Copy)]
+struct Flags {
+    saw_iteration: bool,
+    saw_structure: bool,
+    saw_assignment: bool,
+    saw_macro: bool,
+}
 
-    // Parse the template into AST
-    let ast = match parse(
-        template,
-        "template",
-        SyntaxConfig {},
-        WhitespaceConfig::default(),
-    ) {
-        Ok(ast) => ast,
-        Err(_) => return Some(ChatTemplateContentFormat::String),
-    };
+impl Flags {
+    fn any(self) -> bool {
+        self.saw_iteration || self.saw_structure || self.saw_assignment || self.saw_macro
+    }
+}
 
-    // Traverse AST looking for patterns that indicate OpenAI format
-    let has_iteration = find_content_iteration_in_ast(&ast);
-    let has_structure_checks = find_content_structure_checks_in_ast(&ast);
-    let has_assignment_patterns = find_variable_assignment_patterns_in_ast(&ast);
+/// Single-pass AST detector with scope tracking
+struct Detector<'a> {
+    ast: &'a Stmt<'a>,
+    /// Message loop vars currently in scope (e.g., `message`, `m`, `msg`)
+    scope: std::collections::VecDeque<String>,
+    scope_set: std::collections::HashSet<String>,
+    flags: Flags,
+}
 
-    if has_iteration || has_structure_checks || has_assignment_patterns {
-        Some(ChatTemplateContentFormat::OpenAI)
-    } else {
-        Some(ChatTemplateContentFormat::String)
+impl<'a> Detector<'a> {
+    fn new(ast: &'a Stmt<'a>) -> Self {
+        Self {
+            ast,
+            scope: std::collections::VecDeque::new(),
+            scope_set: std::collections::HashSet::new(),
+            flags: Flags::default(),
+        }
     }
-}
 
-/// Find content iteration patterns in AST
-/// Implements the same logic as SGLang's AST traversal
-fn find_content_iteration_in_ast(ast: &machinery::ast::Stmt) -> bool {
-    use machinery::ast::Stmt;
+    fn run(mut self) -> Flags {
+        self.walk_stmt(self.ast);
+        self.flags
+    }
 
-    match ast {
-        Stmt::Template(template) => {
-            // Recursively check all children
-            template
-                .children
-                .iter()
-                .any(|child| find_content_iteration_in_ast(child))
-        }
-        Stmt::ForLoop(for_loop) => {
-            // Check if this for-loop iterates over message content
-            is_var_or_elems_access(&for_loop.iter, "message", "content") ||
-            is_var_or_elems_access(&for_loop.iter, "msg", "content") ||
-            is_var_or_elems_access(&for_loop.iter, "m", "content") ||
-            // Also check the body for nested loops
-            for_loop.body.iter().any(|stmt| find_content_iteration_in_ast(stmt))
-        }
-        Stmt::IfCond(if_cond) => {
-            // Check true and false branches
-            if_cond
-                .true_body
-                .iter()
-                .any(|stmt| find_content_iteration_in_ast(stmt))
-                || if_cond
-                    .false_body
-                    .iter()
-                    .any(|stmt| find_content_iteration_in_ast(stmt))
+    fn push_scope(&mut self, var: String) {
+        self.scope.push_back(var.clone());
+        self.scope_set.insert(var);
+    }
+
+    fn pop_scope(&mut self) {
+        if let Some(v) = self.scope.pop_back() {
+            self.scope_set.remove(&v);
         }
-        _ => false, // Other statement types don't contain loops
     }
-}
 
-/// Check if expression accesses varname['key'] or varname.key
-/// Implements SGLang's _is_var_or_elems_access logic using actual AST nodes
-fn is_var_or_elems_access(expr: &machinery::ast::Expr, varname: &str, key: &str) -> bool {
-    use machinery::ast::Expr;
+    fn is_var_access(expr: &Expr, varname: &str) -> bool {
+        matches!(expr, Expr::Var(v) if v.id == varname)
+    }
 
-    match expr {
-        // Check for attribute access: varname.key
-        Expr::GetAttr(getattr) => is_var_access(&getattr.expr, varname) && getattr.name == key,
-        // Check for item access: varname['key'] or varname["key"]
-        Expr::GetItem(getitem) => {
-            is_var_access(&getitem.expr, varname) && is_const_string(&getitem.subscript_expr, key)
-        }
-        // Handle filters and tests that might wrap the access
-        Expr::Filter(filter) => {
-            if let Some(ref expr) = filter.expr {
-                is_var_or_elems_access(expr, varname, key)
-            } else {
-                false
+    fn is_const_str(expr: &Expr, value: &str) -> bool {
+        matches!(expr, Expr::Const(c) if c.value.as_str() == Some(value))
     }
+
+    fn is_numeric_const(expr: &Expr) -> bool {
+        matches!(expr, Expr::Const(c) if c.value.is_number())
     }
-        Expr::Test(test) => is_var_or_elems_access(&test.expr, varname, key),
+
+    /// Check if expr is varname.content or varname["content"]
+    fn is_var_dot_content(expr: &Expr, varname: &str) -> bool {
+        match expr {
+            Expr::GetAttr(g) => Self::is_var_access(&g.expr, varname) && g.name == "content",
+            Expr::GetItem(g) => {
+                Self::is_var_access(&g.expr, varname)
+                    && Self::is_const_str(&g.subscript_expr, "content")
+            }
+            // Unwrap filters/tests that just wrap the same expr
+            Expr::Filter(f) => f
+                .expr
+                .as_ref()
+                .is_some_and(|e| Self::is_var_dot_content(e, varname)),
+            Expr::Test(t) => Self::is_var_dot_content(&t.expr, varname),
             _ => false,
         }
-}
+    }
 
-/// Check if expression is a variable access (like {{ varname }})
-/// Implements SGLang's _is_var_access logic
-fn is_var_access(expr: &machinery::ast::Expr, varname: &str) -> bool {
-    matches!(expr, machinery::ast::Expr::Var(var) if var.id == varname)
-}
+    /// Check if expr accesses .content on any variable in our scope, or any descendant of it.
+    fn is_any_scope_var_content(&self, expr: &Expr) -> bool {
+        let mut current_expr = expr;
+        loop {
+            // Check if current level matches <scopeVar>.content
+            if self
+                .scope_set
+                .iter()
+                .any(|v| Self::is_var_dot_content(current_expr, v))
+            {
+                return true;
+            }
+            // Walk up the expression tree
+            match current_expr {
+                Expr::GetAttr(g) => current_expr = &g.expr,
+                Expr::GetItem(g) => current_expr = &g.expr,
+                _ => return false,
+            }
+        }
+    }
 
-/// Check if expression is a constant string with the given value
-fn is_const_string(expr: &machinery::ast::Expr, value: &str) -> bool {
-    matches!(expr, machinery::ast::Expr::Const(const_expr)
-        if const_expr.value.as_str() == Some(value))
-}
+    fn walk_stmt(&mut self, stmt: &Stmt) {
+        // Early exit if we've already detected an OpenAI pattern
+        if self.flags.any() {
+            return;
+        }
 
-/// Find content structure checks in AST (like content[0], content|length)
-fn find_content_structure_checks_in_ast(ast: &machinery::ast::Stmt) -> bool {
-    use machinery::ast::Stmt;
+        match stmt {
+            Stmt::Template(t) => {
+                for ch in &t.children {
+                    self.walk_stmt(ch);
+                }
+            }
+            // {% for message in messages %}
+            Stmt::ForLoop(fl) => {
+                // Detect "for X in messages" → push X into scope
+                if let Expr::Var(iter) = &fl.iter {
+                    if iter.id == "messages" {
+                        if let Expr::Var(target) = &fl.target {
+                            self.push_scope(target.id.to_string());
+                        }
+                    }
+                }
 
-    match ast {
-        Stmt::Template(template) => template
-            .children
-            .iter()
-            .any(|child| find_content_structure_checks_in_ast(child)),
-        Stmt::ForLoop(for_loop) => for_loop
-            .body
-            .iter()
-            .any(|stmt| find_content_structure_checks_in_ast(stmt)),
-        Stmt::IfCond(if_cond) => {
-            // Check if condition has content structure checks
-            has_content_structure_check_expr(&if_cond.expr)
-                || if_cond
-                    .true_body
-                    .iter()
-                    .any(|stmt| find_content_structure_checks_in_ast(stmt))
-                || if_cond
-                    .false_body
-                    .iter()
-                    .any(|stmt| find_content_structure_checks_in_ast(stmt))
+                // Also detect "for ... in message.content" or "for ... in content"
+                // - Iterating directly over <scopeVar>.content => OpenAI style
+                if self.is_any_scope_var_content(&fl.iter) {
+                    self.flags.saw_iteration = true;
                 }
-        Stmt::EmitExpr(expr) => has_content_structure_check_expr(&expr.expr),
-        _ => false,
+                // - Iterating over a local var named "content"
+                if matches!(&fl.iter, Expr::Var(v) if v.id == "content") {
+                    self.flags.saw_iteration = true;
                 }
-}
 
-/// Find variable assignment patterns like set content = message['content']
-fn find_variable_assignment_patterns_in_ast(ast: &machinery::ast::Stmt) -> bool {
-    use machinery::ast::Stmt;
+                for b in &fl.body {
+                    self.walk_stmt(b);
+                }
 
-    match ast {
-        Stmt::Template(template) => template
-            .children
-            .iter()
-            .any(|child| find_variable_assignment_patterns_in_ast(child)),
-        Stmt::ForLoop(for_loop) => {
-            // Check if this for-loop body contains both assignment and iteration
-            let has_assignment = for_loop
-                .body
-                .iter()
-                .any(|stmt| is_content_assignment_stmt(stmt));
-            let has_iteration = for_loop.body.iter().any(|stmt| {
-                is_content_variable_iteration(stmt)
-                    || matches!(stmt, Stmt::IfCond(if_cond) if
-                        if_cond.true_body.iter().any(|s| is_content_variable_iteration(s)) ||
-                        if_cond.false_body.iter().any(|s| is_content_variable_iteration(s))
-                    )
-            });
-
-            (has_assignment && has_iteration)
-                || for_loop
-                    .body
-                    .iter()
-                    .any(|stmt| find_variable_assignment_patterns_in_ast(stmt))
+                // Pop scope if we pushed it
+                if let Expr::Var(iter) = &fl.iter {
+                    if iter.id == "messages" && matches!(&fl.target, Expr::Var(_)) {
+                        self.pop_scope();
                     }
-        Stmt::IfCond(if_cond) => {
-            if_cond
-                .true_body
-                .iter()
-                .any(|stmt| find_variable_assignment_patterns_in_ast(stmt))
-                || if_cond
-                    .false_body
-                    .iter()
-                    .any(|stmt| find_variable_assignment_patterns_in_ast(stmt))
                 }
-        _ => false,
             }
-}
+            Stmt::IfCond(ic) => {
+                self.inspect_expr_for_structure(&ic.expr);
+                for b in &ic.true_body {
+                    self.walk_stmt(b);
+                }
+                for b in &ic.false_body {
+                    self.walk_stmt(b);
+                }
+            }
+            Stmt::EmitExpr(e) => {
+                self.inspect_expr_for_structure(&e.expr);
+            }
+            // {% set content = message.content %}
+            Stmt::Set(s) => {
+                if Self::is_var_access(&s.target, "content")
+                    && self.is_any_scope_var_content(&s.expr)
+                {
+                    self.flags.saw_assignment = true;
+                }
+            }
+            Stmt::Macro(m) => {
+                // Heuristic: macro that checks type (via `is` test) and also has any loop
+                let mut has_type_check = false;
+                let mut has_loop = false;
+                Self::scan_macro_body(&m.body, &mut has_type_check, &mut has_loop);
+                if has_type_check && has_loop {
+                    self.flags.saw_macro = true;
+                }
+            }
+            _ => {}
+        }
+    }
 
-/// Check if expression has content structure checks (index access, length, etc.)
-fn has_content_structure_check_expr(expr: &machinery::ast::Expr) -> bool {
-    use machinery::ast::Expr;
+    fn inspect_expr_for_structure(&mut self, expr: &Expr) {
+        if self.flags.saw_structure {
+            return;
+        }
 
         match expr {
-        // Check for content[0] - index access
-        Expr::GetItem(getitem) => {
-            is_content_access(&getitem.expr) && is_numeric_constant(&getitem.subscript_expr)
-        }
-        // Check for content|length - filter with length
-        Expr::Filter(filter) => {
-            if let Some(ref filter_expr) = filter.expr {
-                is_content_access(filter_expr) && filter.name == "length"
+            // content[0] or message.content[0]
+            Expr::GetItem(gi) => {
+                if (matches!(&gi.expr, Expr::Var(v) if v.id == "content")
+                    || self.is_any_scope_var_content(&gi.expr))
+                    && Self::is_numeric_const(&gi.subscript_expr)
+                {
+                    self.flags.saw_structure = true;
+                }
+            }
+            // content|length or message.content|length
+            Expr::Filter(f) => {
+                if f.name == "length" {
+                    if let Some(inner) = &f.expr {
+                        // Box derefs automatically, so `&**inner` is `&Expr`
+                        let inner_ref: &Expr = inner;
+                        let is_content_var = matches!(inner_ref, Expr::Var(v) if v.id == "content");
+                        if is_content_var || self.is_any_scope_var_content(inner_ref) {
+                            self.flags.saw_structure = true;
+                        }
+                    }
+                } else if let Some(inner) = &f.expr {
+                    let inner_ref: &Expr = inner;
+                    self.inspect_expr_for_structure(inner_ref);
+                }
+            }
+            // content is sequence/iterable OR message.content is sequence/iterable
+            Expr::Test(t) => {
+                if t.name == "sequence" || t.name == "iterable" || t.name == "string" {
+                    if matches!(&t.expr, Expr::Var(v) if v.id == "content")
+                        || self.is_any_scope_var_content(&t.expr)
+                    {
+                        self.flags.saw_structure = true;
+                    }
                 } else {
-                false
+                    self.inspect_expr_for_structure(&t.expr);
                 }
             }
-        // Check for content is sequence/iterable
-        Expr::Test(test) => {
-            is_content_access(&test.expr) && (test.name == "sequence" || test.name == "iterable")
+            Expr::GetAttr(g) => {
+                // Keep walking; nested expressions can hide structure checks
+                self.inspect_expr_for_structure(&g.expr);
             }
-        _ => false,
+            // Handle binary operations like: if (message.content is string) and other_cond
+            Expr::BinOp(op) => {
+                self.inspect_expr_for_structure(&op.left);
+                self.inspect_expr_for_structure(&op.right);
             }
-}
-
-/// Check if statement assigns message content to a variable
-fn is_content_assignment_stmt(stmt: &machinery::ast::Stmt) -> bool {
-    use machinery::ast::Stmt;
-
-    match stmt {
-        Stmt::Set(set_stmt) => {
-            // Check if this is setting content = message['content']
-            is_var_access(&set_stmt.target, "content")
-                && is_var_or_elems_access(&set_stmt.expr, "message", "content")
+            // Handle unary operations like: if not (message.content is string)
+            Expr::UnaryOp(op) => {
+                self.inspect_expr_for_structure(&op.expr);
+            }
+            _ => {}
         }
-        _ => false,
     }
-}
 
-/// Check if statement iterates over content variable
-fn is_content_variable_iteration(stmt: &machinery::ast::Stmt) -> bool {
-    use machinery::ast::{Expr, Stmt};
+    fn scan_macro_body(body: &[Stmt], has_type_check: &mut bool, has_loop: &mut bool) {
+        for s in body {
+            if *has_type_check && *has_loop {
+                return;
+            }
 
-    match stmt {
-        Stmt::ForLoop(for_loop) => {
-            // Check if iterating over a variable named "content"
-            matches!(for_loop.iter, Expr::Var(ref var) if var.id == "content")
+            match s {
+                Stmt::IfCond(ic) => {
+                    if matches!(&ic.expr, Expr::Test(_)) {
+                        *has_type_check = true;
+                    }
+                    Self::scan_macro_body(&ic.true_body, has_type_check, has_loop);
+                    Self::scan_macro_body(&ic.false_body, has_type_check, has_loop);
+                }
+                Stmt::ForLoop(fl) => {
+                    *has_loop = true;
+                    Self::scan_macro_body(&fl.body, has_type_check, has_loop);
+                }
+                Stmt::Template(t) => {
+                    Self::scan_macro_body(&t.children, has_type_check, has_loop);
+                }
+                _ => {}
+            }
         }
-        _ => false,
     }
 }
 
-/// Check if expression accesses content (message.content, message['content'], etc.)
-fn is_content_access(expr: &machinery::ast::Expr) -> bool {
-    is_var_or_elems_access(expr, "message", "content")
-        || is_var_or_elems_access(expr, "msg", "content")
-        || is_var_or_elems_access(expr, "m", "content")
-}
+/// AST-based detection using minijinja's unstable machinery
+/// Single-pass detector with scope tracking
+fn detect_format_with_ast(template: &str) -> Option<ChatTemplateContentFormat> {
+    use minijinja::machinery::{parse, WhitespaceConfig};
+    use minijinja::syntax::SyntaxConfig;
 
-/// Check if expression is a numeric constant (for index access)
-fn is_numeric_constant(expr: &machinery::ast::Expr) -> bool {
-    matches!(expr, machinery::ast::Expr::Const(const_expr) if const_expr.value.is_number())
+    let ast = match parse(
+        template,
+        "template",
+        SyntaxConfig {},
+        WhitespaceConfig::default(),
+    ) {
+        Ok(ast) => ast,
+        Err(_) => return Some(ChatTemplateContentFormat::String),
+    };
+
+    let flags = Detector::new(&ast).run();
+    Some(if flags.any() {
+        ChatTemplateContentFormat::OpenAI
+    } else {
+        ChatTemplateContentFormat::String
+    })
 }
 
 /// Parameters for chat template application

sgl-router/tests/chat_template_format_detection.rs

@@ -249,3 +249,65 @@ fn test_chat_template_with_tokens_unit_test() {
     assert!(result.contains("<s>"));
     assert!(result.contains("</s>"));
 }
+
+#[test]
+fn test_detect_openai_format_qwen3vl_macro_style() {
+    // Qwen3-VL style template using macros to handle multimodal content
+    // This tests the macro-based detection pattern
+    let template = r#"{%- set image_count = namespace(value=0) %}
+{%- set video_count = namespace(value=0) %}
+{%- macro render_content(content, do_vision_count) %}
+    {%- if content is string %}
+        {{- content }}
+    {%- else %}
+        {%- for item in content %}
+            {%- if 'image' in item or 'image_url' in item or item.type == 'image' %}
+                {%- if do_vision_count %}
+                    {%- set image_count.value = image_count.value + 1 %}
+                {%- endif %}
+                {%- if add_vision_id %}Picture {{ image_count.value }}: {% endif -%}
+                <|vision_start|><|image_pad|><|vision_end|>
+            {%- elif 'video' in item or item.type == 'video' %}
+                {%- if do_vision_count %}
+                    {%- set video_count.value = video_count.value + 1 %}
+                {%- endif %}
+                {%- if add_vision_id %}Video {{ video_count.value }}: {% endif -%}
+                <|vision_start|><|video_pad|><|vision_end|>
+            {%- elif 'text' in item %}
+                {{- item.text }}
+            {%- endif %}
+        {%- endfor %}
+    {%- endif %}
+{%- endmacro %}
+{%- for message in messages %}
+    {%- set content = render_content(message.content, True) %}
+    {{- '<|im_start|>' + message.role + '\n' + content + '<|im_end|>' + '\n' }}
+{%- endfor %}
+{%- if add_generation_prompt %}
+    {{- '<|im_start|>assistant\n' }}
+{%- endif %}"#;
+
+    assert_eq!(
+        detect_chat_template_content_format(template),
+        ChatTemplateContentFormat::OpenAI
+    );
+}
+
+#[test]
+fn test_detect_openai_format_arbitrary_variable_names() {
+    // Test that detection works with any variable name, not just "message", "msg", "m"
+    // Uses "chat_msg" and "x" as loop variables
+    let template = r#"
+        {%- for chat_msg in messages %}
+        {%- for x in chat_msg.content %}
+        {%- if x.type == 'text' %}{{ x.text }}{%- endif %}
+        {%- if x.type == 'image' %}<image>{%- endif %}
+        {%- endfor %}
+        {%- endfor %}
+        "#;
+
+    assert_eq!(
+        detect_chat_template_content_format(template),
+        ChatTemplateContentFormat::OpenAI
+    );
+}