From 88178a7dbe5bbedc24d672fc3e0a2d9a3086048f Mon Sep 17 00:00:00 2001
From: Rico Tzschichholz <ricotz@ubuntu.com>
Date: Sun, 1 Nov 2020 21:16:49 +0100
Subject: vala: Use DataType.compatible() to check for string concatenation

Make the checks match the ones performed by the code-generator to prevent
invalid c-code to be created.

See https://gitlab.gnome.org/GNOME/vala/issues/1100
---
 tests/Makefile.am                          |  2 ++
 tests/basic-types/pointers-arithmetic.vala | 22 ++++++++++++++++++++++
 tests/nullability/string-concat.test       |  6 ++++++
 vala/valabinaryexpression.vala             |  6 +++---
 4 files changed, 33 insertions(+), 3 deletions(-)
 create mode 100644 tests/basic-types/pointers-arithmetic.vala
 create mode 100644 tests/nullability/string-concat.test

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 168a3fe6e..57020feee 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -35,6 +35,7 @@ TESTS = \
 	basic-types/arrays-fixed-assignment.vala \
 	basic-types/array-uint8-uchar-compat.vala \
 	basic-types/pointers.vala \
+	basic-types/pointers-arithmetic.vala \
 	basic-types/sizeof.vala \
 	basic-types/garray.vala \
 	basic-types/glists.vala \
@@ -1026,6 +1027,7 @@ NON_NULL_TESTS = \
 	nullability/member-access-nullable-instance.test \
 	nullability/method-parameter-invalid-convert.test \
 	nullability/method-return-invalid-convert.test \
+	nullability/string-concat.test \
 	nullability/with-non-null.test \
 	$(NULL)
 
diff --git a/tests/basic-types/pointers-arithmetic.vala b/tests/basic-types/pointers-arithmetic.vala
new file mode 100644
index 000000000..79437f087
--- /dev/null
+++ b/tests/basic-types/pointers-arithmetic.vala
@@ -0,0 +1,22 @@
+void test_chars () {
+	char* s = "foo";
+	char* begin = s;
+	char* end = begin + 2;
+
+	assert (begin[0] == 'f');
+	assert (end[0] == 'o');
+}
+
+void test_strings () {
+	string s = "foo";
+	string* begin = s;
+	string* end = begin + s.length - 1;
+
+	assert (((char*) begin)[0] == 'f');
+	assert (((char*) end)[0] == 'o');
+}
+
+void main () {
+	test_chars ();
+	test_strings ();
+}
diff --git a/tests/nullability/string-concat.test b/tests/nullability/string-concat.test
new file mode 100644
index 000000000..5cc78efc6
--- /dev/null
+++ b/tests/nullability/string-concat.test
@@ -0,0 +1,6 @@
+Invalid Code
+
+void main () {
+	string? foo = null;
+	string bar = foo + "bar";
+}
diff --git a/vala/valabinaryexpression.vala b/vala/valabinaryexpression.vala
index 7b9b78214..f831c7cb7 100644
--- a/vala/valabinaryexpression.vala
+++ b/vala/valabinaryexpression.vala
@@ -350,11 +350,11 @@ public class Vala.BinaryExpression : Expression {
 		right.target_type = right.value_type.copy ();
 		right.target_type.value_owned = false;
 
-		if (operator == BinaryOperator.PLUS
-		    && left.value_type.type_symbol == context.analyzer.string_type.type_symbol) {
+		if (operator == BinaryOperator.PLUS && !(left.value_type is PointerType)
+		    && left.value_type.compatible (context.analyzer.string_type)) {
 			// string concatenation
 
-			if (right.value_type == null || right.value_type.type_symbol != context.analyzer.string_type.type_symbol) {
+			if (right.value_type == null || !right.value_type.compatible (context.analyzer.string_type)) {
 				error = true;
 				Report.error (source_reference, "Operands must be strings");
 				return false;
-- 
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