1 files changed, 28 insertions, 0 deletions
diff --git a/third_party/python/fluent.migrate/fluent/migrate/evaluator.py b/third_party/python/fluent.migrate/fluent/migrate/evaluator.py
new file mode 100644
index 0000000000..90c626f933
--- /dev/null
+++ b/third_party/python/fluent.migrate/fluent/migrate/evaluator.py
@@ -0,0 +1,28 @@
+from fluent.syntax import ast as FTL
+from fluent.syntax.visitor import Transformer
+
+from .transforms import Transform
+
+
+class Evaluator(Transformer):
+    """An AST transformer for evaluating migration Transforms.
+
+    An AST transformer (i.e. a visitor capable of modifying the AST) which
+    walks an AST hierarchy and evaluates nodes which are migration Transforms.
+    """
+
+    def __init__(self, ctx):
+        self.ctx = ctx
+
+    def visit(self, node):
+        if not isinstance(node, FTL.BaseNode):
+            return node
+
+        if isinstance(node, Transform):
+            # Some transforms don't expect other transforms as children.
+            # Evaluate the children first.
+            transform = self.generic_visit(node)
+            # Then, evaluate this transform.
+            return transform(self.ctx)
+
+        return self.generic_visit(node)