Add upgrade script moving superclass exprs to own table

.codeqlmanifest.json

@@ -1,6 +1,9 @@
-{ "provide": [ "ql/src/qlpack.yml",
-               "ql/test/qlpack.yml",
-               "ql/examples/qlpack.yml",
-               "extractor-pack/codeql-extractor.yml"
-             ]
-}
+{
+    "provide": [
+        "ql/src/qlpack.yml",
+        "ql/test/qlpack.yml",
+        "ql/examples/qlpack.yml",
+        "upgrades/qlpack.yml",
+        "extractor-pack/codeql-extractor.yml"
+    ]
+}

upgrades/5df84541a21ef20b2c8d7b73de0e4b9720c45642/class_child.ql

@@ -0,0 +1,26 @@
+class Superclass extends @superclass {
+  string toString() { result = "" }
+}
+
+class Class extends @class {
+  string toString() { result = "" }
+}
+
+class ClassChildType extends @class_child_type {
+  string toString() { result = "" }
+}
+
+// Select all non-superclass children.
+// If the 0th child is a superclass, shuffle all the indexes down one. (Having
+// superclass children at other indexes is allowed in the old dbscheme, but
+// doesn't happen in practice, given the tree-sitter grammar).
+from Class c, int oldIndex, ClassChildType child, int newIndex
+where
+  class_child(c, oldIndex, child) and
+  (
+    if exists(Superclass sc | class_child(c, 0, sc))
+    then newIndex = oldIndex - 1
+    else newIndex = oldIndex
+  ) and
+  not child instanceof Superclass
+select c, newIndex, child

upgrades/5df84541a21ef20b2c8d7b73de0e4b9720c45642/class_superclass.ql

@@ -0,0 +1,12 @@
+class Superclass extends @superclass {
+  string toString() { result = "" }
+}
+
+class Class extends @class {
+  string toString() { result = "" }
+}
+
+// Select the 0th child if it's a @superclass
+from Class c, Superclass sc
+where class_child(c, 0, sc)
+select c, sc

upgrades/5df84541a21ef20b2c8d7b73de0e4b9720c45642/upgrade.properties

@@ -0,0 +1,4 @@
+description: moves class superclass nodes into their own table
+compatibility: full
+class_superclass.rel: run class_superclass.qlo
+class_child.rel: run class_child.qlo

upgrades/qlpack.yml

@@ -0,0 +1,2 @@
+name: codeql-ruby-upgrades
+upgrades: .