C#: Improve downgrade script.

csharp/downgrades/66044cfa5bbf2ecfabd06ead25e91db2bdd79764/expressions.ql

@@ -1,13 +0,0 @@
-class Expression extends @expr {
-  string toString() { none() }
-}
-
-class TypeOrRef extends @type_or_ref {
-  string toString() { none() }
-}
-
-from Expression e, int k, int kind, TypeOrRef t
-where
-  expressions(e, k, t) and
-  if k = 138 then kind = 106 else kind = k
-select e, kind, t

csharp/downgrades/66044cfa5bbf2ecfabd06ead25e91db2bdd79764/string_interpol_insert.ql

@@ -0,0 +1,39 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class TypeOrRef extends @type_or_ref {
+  string toString() { none() }
+}
+
+class InterpolatedStringInsertExpr extends Expr, @interpolated_string_insert_expr { }
+
+private predicate remove_expr(Expr e) {
+  exists(InterpolatedStringInsertExpr ie |
+    e = ie
+    or
+    // Alignment
+    expr_parent(e, 1, ie)
+    or
+    // Format
+    expr_parent(e, 2, ie)
+  )
+}
+
+query predicate new_expressions(Expr e, int kind, TypeOrRef t) {
+  expressions(e, kind, t) and
+  // Remove the syntheetic intert expression and previously un-extracted children
+  not remove_expr(e)
+}
+
+query predicate new_expr_parent(Expr e, int child, Expr parent) {
+  expr_parent(e, child, parent) and
+  not remove_expr(e) and
+  not remove_expr(parent)
+  or
+  // Use the string interpolation as parent instead of the synthetic insert expression
+  exists(InterpolatedStringInsertExpr ie |
+    expr_parent(e, 0, ie) and
+    expr_parent(ie, child, parent)
+  )
+}

csharp/downgrades/66044cfa5bbf2ecfabd06ead25e91db2bdd79764/upgrade.properties

@@ -1,3 +1,4 @@
 description: Remove `interpolated_string_insert_expr` kind.
-compatibility: partial
-expressions.rel: run expressions.qlo
+compatibility: backwards
+expressions.rel: run string_interpol_insert.qlo new_expressions
+expr_parent.rel: run string_interpol_insert.qlo new_expr_parent