vala: Add support for null-safe access operator

This implements support for the "null-safe" operator of C#
(also called "safe navigation" operator).

  var foo = bar?.foo;
  var foo = bar?.foo();
  var foo = bar?[3];
  var foo = bar?[1:2];

It applies to plain member access, method calls, element access and
slice expressions (including void method calls, which are simply bypassed
if the inner expression is null).

Fixes https://gitlab.gnome.org/GNOME/vala/issues/522

1 files changed, 10 insertions, 0 deletions

diff --git a/vala/valasliceexpression.vala b/vala/valasliceexpression.vala
index a9502b3e8..98b009b5e 100644
--- a/vala/valasliceexpression.vala
+++ b/vala/valasliceexpression.vala
@@ -60,6 +60,11 @@ public class Vala.SliceExpression : Expression {
 		}
 	}
 
+	/**
+	 * Null-safe access.
+	 */
+	public bool null_safe_access { get; set; }
+
 	Expression _container;
 	Expression _start;
 	Expression _stop;
@@ -111,6 +116,11 @@ public class Vala.SliceExpression : Expression {
 
 		checked = true;
 
+		if (null_safe_access) {
+			error = !base.check (context);
+			return !error;
+		}
+
 		if (!container.check (context)) {
 			error = true;
 			return false;