Merge pull request github#14671 from smowton/smowton/feature/jdk21-switch-pattern-matching

Java: Add support for Java 21 language features

Author: smowton

java/downgrades/dee651b58d1e5455ca2d07eca37775a21d772fcc/exprs.ql

@@ -0,0 +1,55 @@
+class Expr extends @expr {
+  string toString() { result = "expr" }
+}
+
+class LocalVariableDeclExpr extends @localvariabledeclexpr, Expr { }
+
+class InstanceOfExpr extends @instanceofexpr, Expr { }
+
+class SimplePatternInstanceOfExpr extends InstanceOfExpr {
+  SimplePatternInstanceOfExpr() { getNthChild(this, 2) instanceof LocalVariableDeclExpr }
+}
+
+class Type extends @type {
+  string toString() { result = "type" }
+}
+
+class ExprParent extends @exprparent {
+  string toString() { result = "exprparent" }
+}
+
+Expr getNthChild(ExprParent parent, int i) { exprs(result, _, _, parent, i) }
+
+// Where an InstanceOfExpr has a 2nd child that is a LocalVariableDeclExpr, that expression should becomes its 0th child and the existing 0th child should become its initialiser.
+// Any RecordPatternExpr should be replaced with an error expression, as it can't be represented in the downgraded dbscheme.
+// This reverts a reorganisation of the representation of "o instanceof String s", which used to be InstanceOfExpr -0-> LocalVariableDeclExpr --init-> o
+//                                                                                                                                               \-name-> s
+// It is now InstanceOfExpr --0-> o
+//                          \-2-> LocalVariableDeclExpr -name-> s
+//
+// Other children are unaffected.
+predicate hasNewParent(Expr e, ExprParent newParent, int newIndex) {
+  exists(SimplePatternInstanceOfExpr oldParent, int oldIndex |
+    e = getNthChild(oldParent, oldIndex)
+  |
+    oldIndex = 0 and newParent = getNthChild(oldParent, 2) and newIndex = 0
+    or
+    oldIndex = 1 and newParent = oldParent and newIndex = oldIndex
+    or
+    oldIndex = 2 and newParent = oldParent and newIndex = 0
+  )
+  or
+  not exists(SimplePatternInstanceOfExpr oldParent | e = getNthChild(oldParent, _)) and
+  exprs(e, _, _, newParent, newIndex)
+}
+
+from Expr e, int oldKind, int newKind, Type typeid, ExprParent parent, int index
+where
+  exprs(e, oldKind, typeid, _, _) and
+  hasNewParent(e, parent, index) and
+  (
+    if oldKind = /* record pattern */ 89
+    then newKind = /* error expression */ 74
+    else oldKind = newKind
+  )
+select e, newKind, typeid, parent, index