Add new flatten method so we can generate notes in semconv

crates/weaver_forge/expected_output/attribute_groups.md

@@ -1,6 +1,9 @@
 # Semantic Convention Attribute Groups
 
-
+## flatten
+- one
+- two
+- three
 ## Group `attributes.jvm.memory` (attribute_group)
 
 ### Brief

crates/weaver_forge/src/lib.rs

@@ -355,6 +355,7 @@ impl TemplateEngine {
             "field_name",
             case_converter(self.target_config.field_name.clone()),
         );
+        env.add_filter("flatten", flatten);
 
         // env.add_filter("unique_attributes", extensions::unique_attributes);
         // env.add_filter("instrument", extensions::instrument);
@@ -408,6 +409,18 @@ impl TemplateEngine {
     }
 }
 
+// Helper filter to work around lack of `list.append()` support in minijinja.
+// Will take a list of lists and return a new list containing only elements of sublists.
+fn flatten(value: Value) -> Result<Value, minijinja::Error> {
+    let mut result = Vec::new();
+    for sublist in value.try_iter()? {
+        for item in sublist.try_iter()? {
+            result.push(item);
+        }
+    }
+    Ok(Value::from(result))
+}
+
 #[cfg(test)]
 mod tests {
     use std::collections::HashSet;

crates/weaver_forge/templates/test/attribute_groups.md

@@ -1,5 +1,11 @@
 # Semantic Convention Attribute Groups
 
+## flatten
+{%- set test = [["one", "two"], ["three"]] | flatten -%}
+{% for item in test %}
+- {{item}}
+{%- endfor -%}
+
 {% for group in ctx %}
 ## Group `{{ group.id }}` ({{ group.type }})
 

crates/weaver_forge/templates/test/weaver.yaml

@@ -12,4 +12,4 @@ type_mapping:
   "int[]": "[]int64"
   "double[]": "[]double"
   "boolean[]": "[]bool"
-  "string[]": "[]string"
+  "string[]": "[]string"