[Attention] Add FlashInfer Sparse MLA backend (#33451)

Signed-off-by: Matthew Bonanni <mbonanni@redhat.com>
Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
Co-authored-by: Lucas Wilkinson <lwilkins@redhat.com>
Co-authored-by: Lucas Wilkinson <LucasWilkinson@users.noreply.github.com>

tools/pre_commit/generate_attention_backend_docs.py

@@ -901,10 +901,50 @@ def parse_cuda_priority_lists() -> dict[str, list[str]]:
 
 
 def _get_backends_from_return(stmts: list) -> list[str]:
-    """Extract backend names from return statements in a list of statements."""
+    """Extract backend names from return statements in a list of statements.
+
+    Handles starred unpacking (e.g. ``*sparse_backends``) by resolving the
+    variable from assignments found in the same statement list.  When the
+    variable is conditionally assigned (inside an ``if/else``), the ``else``
+    branch value is used as the representative default.
+    """
+    # Collect variable assignments so we can resolve starred expressions.
+    # For conditional assignments, last-written (else branch) wins.
+    var_assigns: dict[str, list[str]] = {}
+    for stmt in stmts:
+        if isinstance(stmt, ast.Assign) and isinstance(stmt.value, ast.List):
+            for target in stmt.targets:
+                if isinstance(target, ast.Name):
+                    var_assigns[target.id] = [
+                        e.attr for e in stmt.value.elts if isinstance(e, ast.Attribute)
+                    ]
+        elif isinstance(stmt, ast.If):
+            for branch in (stmt.body, stmt.orelse):
+                for branch_stmt in branch:
+                    if isinstance(branch_stmt, ast.Assign) and isinstance(
+                        branch_stmt.value, ast.List
+                    ):
+                        for target in branch_stmt.targets:
+                            if isinstance(target, ast.Name):
+                                var_assigns[target.id] = [
+                                    e.attr
+                                    for e in branch_stmt.value.elts
+                                    if isinstance(e, ast.Attribute)
+                                ]
+
     for stmt in stmts:
         if isinstance(stmt, ast.Return) and isinstance(stmt.value, ast.List):
-            return [e.attr for e in stmt.value.elts if isinstance(e, ast.Attribute)]
+            backends: list[str] = []
+            for e in stmt.value.elts:
+                if isinstance(e, ast.Attribute):
+                    backends.append(e.attr)
+                elif (
+                    isinstance(e, ast.Starred)
+                    and isinstance(e.value, ast.Name)
+                    and e.value.id in var_assigns
+                ):
+                    backends.extend(var_assigns[e.value.id])
+            return backends
     return []