Python: add YAML library

Author: aibaars

python/ql/lib/qlpack.yml

@@ -9,5 +9,6 @@ dependencies:
   codeql/regex: ${workspace}
   codeql/tutorial: ${workspace}
   codeql/util: ${workspace}
+  codeql/yaml: ${workspace}
 dataExtensions:
   - semmle/python/frameworks/**/model.yml

python/ql/lib/semmle/python/YAML.qll

@@ -0,0 +1,50 @@
+/**
+ * Provides classes for working with YAML data.
+ *
+ * YAML documents are represented as abstract syntax trees whose nodes
+ * are either YAML values or alias nodes referring to another YAML value.
+ */
+
+private import codeql.yaml.Yaml as LibYaml
+
+private module YamlSig implements LibYaml::InputSig {
+  import semmle.python.Files
+
+  class LocatableBase extends @yaml_locatable {
+    Location getLocation() { yaml_locations(this, result) }
+
+    string toString() { none() }
+  }
+
+  class NodeBase extends LocatableBase, @yaml_node {
+    NodeBase getChildNode(int i) { yaml(result, _, this, i, _, _) }
+
+    string getTag() { yaml(this, _, _, _, result, _) }
+
+    string getAnchor() { yaml_anchors(this, result) }
+
+    override string toString() { yaml(this, _, _, _, _, result) }
+  }
+
+  class ScalarNodeBase extends NodeBase, @yaml_scalar_node {
+    int getStyle() { yaml_scalars(this, result, _) }
+
+    string getValue() { yaml_scalars(this, _, result) }
+  }
+
+  class CollectionNodeBase extends NodeBase, @yaml_collection_node { }
+
+  class MappingNodeBase extends CollectionNodeBase, @yaml_mapping_node { }
+
+  class SequenceNodeBase extends CollectionNodeBase, @yaml_sequence_node { }
+
+  class AliasNodeBase extends NodeBase, @yaml_alias_node {
+    string getTarget() { yaml_aliases(this, result) }
+  }
+
+  class ParseErrorBase extends LocatableBase, @yaml_error {
+    string getMessage() { yaml_errors(this, result) }
+  }
+}
+
+import LibYaml::Make<YamlSig>