C#: Add type Global value number kinds for control flow elements.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/commons/StructuralComparison.qll

@@ -4,3 +4,69 @@
  */
 
 import csharp
+
+private newtype TGvnKind =
+  TGvnKindExpr(int kind) { expressions(_, kind, _) } or
+  TGvnKindStmt(int kind) { statements(_, kind) } or
+  TGvnKindDeclaration(GvnKindExpr kind, boolean thisTarget, Declaration d) {
+    exists(Expr e |
+      d = referenceAttribute(e) and thisTarget = isTargetThis(e) and kind = getKind(e)
+    )
+  }
+
+abstract private class GvnKind extends TGvnKind {
+  abstract string toString();
+}
+
+private class GvnKindExpr extends GvnKind, TGvnKindExpr {
+  private int kind;
+
+  GvnKindExpr() { this = TGvnKindExpr(kind) }
+
+  override string toString() { result = "Expr(" + kind.toString() + ")" }
+}
+
+private class GvnKindStmt extends GvnKind, TGvnKindStmt {
+  private int kind;
+
+  GvnKindStmt() { this = TGvnKindStmt(kind) }
+
+  override string toString() { result = "Stmt(" + kind.toString() + ")" }
+}
+
+private class GvnKindDeclaration extends GvnKind, TGvnKindDeclaration {
+  private GvnKindExpr kind;
+  private boolean isTargetThis;
+  private Declaration d;
+
+  GvnKindDeclaration() { this = TGvnKindDeclaration(kind, isTargetThis, d) }
+
+  override string toString() { result = kind.toString() + "," + isTargetThis + "," + d.toString() }
+}
+
+/** Gets the declaration referenced by the expression `e`, if any. */
+private Declaration referenceAttribute(Expr e) {
+  result = e.(MethodCall).getTarget()
+  or
+  result = e.(ObjectCreation).getTarget()
+  or
+  result = e.(Access).getTarget()
+}
+
+/** Returns true iff the target of the expression `e` is `this`. */
+private boolean isTargetThis(Expr e) {
+  result = true and e.(MemberAccess).targetIsThisInstance()
+  or
+  result = false and not e.(MemberAccess).targetIsThisInstance()
+}
+
+/** Gets the AST node kind of element `cfe` wrapped in the GvnKind type. */
+private GvnKind getKind(ControlFlowElement cfe) {
+  exists(int kind |
+    expressions(cfe, kind, _) and
+    result = TGvnKindExpr(kind)
+    or
+    statements(cfe, kind) and
+    result = TGvnKindStmt(kind)
+  )
+}