From 50748111d26d839cb8244e1bfc0c6924305a90b1 Mon Sep 17 00:00:00 2001
From: Marvin W <git@larma.de>
Date: Tue, 11 Apr 2017 17:19:58 +0200
Subject: [PATCH] vala: Handle non-null in coalescing expression

https://bugzilla.gnome.org/show_bug.cgi?id=611223
---
 tests/Makefile.am                |  8 +++++++-
 tests/nullability/bug611223.vala |  7 +++++++
 vala/valabinaryexpression.vala   | 33 ++++++++++++++++++++++++++++----
 3 files changed, 43 insertions(+), 5 deletions(-)
 create mode 100644 tests/nullability/bug611223.vala

diff --git a/tests/Makefile.am b/tests/Makefile.am
index e368b6b95..2a2f4d43c 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -286,11 +286,17 @@ TESTS = \
 	annotations/description.vala \
 	$(NULL)
 
-check-TESTS: $(TESTS)
+NON_NULL_TESTS = \
+	nullability/bug611223.vala \
+	$(NULL)
+
+check-TESTS: $(TESTS) $(NON_NULL_TESTS)
 	@EXEEXT=$(EXEEXT) EXEEXT=$(EXEEXT) CFLAGS='$(CFLAGS)' CPPFLAGS='$(CPPFLAGS)' LDFLAGS='$(LDFLAGS)' $(srcdir)/testrunner.sh $(TESTS)
+	@EXEEXT=$(EXEEXT) EXEEXT=$(EXEEXT) CFLAGS='$(CFLAGS)' CPPFLAGS='$(CPPFLAGS)' LDFLAGS='$(LDFLAGS)' VALAFLAGS="--enable-experimental-non-null" $(srcdir)/testrunner.sh $(NON_NULL_TESTS)
 
 EXTRA_DIST = \
 	testrunner.sh \
 	$(TESTS) \
+	$(NON_NULL_TESTS) \
 	$(NULL)
 
diff --git a/tests/nullability/bug611223.vala b/tests/nullability/bug611223.vala
new file mode 100644
index 000000000..9fbf30c07
--- /dev/null
+++ b/tests/nullability/bug611223.vala
@@ -0,0 +1,7 @@
+void main() {
+	string? nullable = null;
+	string non_null = nullable ?? "";
+	string? some_null = nullable ?? null;
+	string also_non_null = null ?? non_null;
+	string really_non_null = non_null ?? nullable;
+}
diff --git a/vala/valabinaryexpression.vala b/vala/valabinaryexpression.vala
index 82e605398..19287da85 100644
--- a/vala/valabinaryexpression.vala
+++ b/vala/valabinaryexpression.vala
@@ -210,12 +210,31 @@ public class Vala.BinaryExpression : Expression {
 			}
 
 			DataType local_type = null;
-			if (left.value_type != null) {
+			bool cast_non_null = false;
+			if (left.value_type is NullType && right.value_type != null) {
+				Report.warning (left.source_reference, "left operand is always null");
+				local_type = right.value_type.copy ();
+				local_type.nullable = true;
+				if (!right.value_type.nullable) {
+					cast_non_null = true;
+				}
+			} else if (left.value_type != null) {
 				local_type = left.value_type.copy ();
 				if (right.value_type != null && right.value_type.value_owned) {
 					// value owned if either left or right is owned
 					local_type.value_owned = true;
 				}
+				if (context.experimental_non_null) {
+					if (!local_type.nullable) {
+						Report.warning (left.source_reference, "left operand is never null");
+						if (right.value_type != null && right.value_type.nullable) {
+							local_type.nullable = true;
+							cast_non_null = true;
+						}
+					} else if (right.value_type != null && !right.value_type.nullable) {
+						cast_non_null = true;
+					}
+				}
 			} else if (right.value_type != null) {
 				local_type = right.value_type.copy ();
 			}
@@ -246,10 +265,16 @@ public class Vala.BinaryExpression : Expression {
 				return false;
 			}
 
-			var temp_access = SemanticAnalyzer.create_temp_access (local, target_type);
-			temp_access.check (context);
+			var replace_expr = SemanticAnalyzer.create_temp_access (local, target_type);
+			if (cast_non_null && replace_expr.target_type != null) {
+				var cast = new CastExpression.non_null (replace_expr, source_reference);
+				cast.target_type = replace_expr.target_type.copy ();
+				cast.target_type.nullable = false;
+				replace_expr = cast;
+			}
+			replace_expr.check (context);
 
-			parent_node.replace_expression (this, temp_access);
+			parent_node.replace_expression (this, replace_expr);
 
 			return true;
 		}
-- 
2.47.2