From e5d9e61fcde02e4b40f96b91df06abf796b2587d Mon Sep 17 00:00:00 2001
From: Michael Lill <michael.lill@tokiwa.software>
Date: Thu, 3 Aug 2023 14:52:17 +0200
Subject: [PATCH 1/2] improve backward type propagation for arrays - fixes #169

---
 src/dev/flang/ast/InlineArray.java            |  6 ++---
 .../Makefile                                  | 27 +++++++++++++++++++
 .../issue169.fz                               | 16 +++++++++++
 3 files changed, 46 insertions(+), 3 deletions(-)
 create mode 100644 tests/reg_issue169_backward_type_propagation_array/Makefile
 create mode 100644 tests/reg_issue169_backward_type_propagation_array/issue169.fz

diff --git a/src/dev/flang/ast/InlineArray.java b/src/dev/flang/ast/InlineArray.java
index 7807a7b72..e589ac751 100644
--- a/src/dev/flang/ast/InlineArray.java
+++ b/src/dev/flang/ast/InlineArray.java
@@ -119,7 +119,7 @@ AbstractType typeIfKnown()
                                               _elements.iterator());
             _type = Types.t_ERROR;
           }
-        if (_type == null)
+        else
           {
             _type =
               t == null ? null :
@@ -162,7 +162,7 @@ public Expr propagateExpectedType(Resolution res, AbstractFeature outer, Abstrac
               {
                 e.propagateExpectedType(res, outer, elementType);
               }
-            _type = t;
+            _type = Types.resolved.f_array.resultTypeIfPresent(res, new List<>(elementType));
           }
       }
     return this;
@@ -181,7 +181,7 @@ private AbstractType elementType(AbstractType t)
     if (PRECONDITIONS) require
       (t != null);
 
-    if (t.featureOfType() == Types.resolved.f_array &&
+    if (Types.resolved.f_array.inheritsFrom(t.featureOfType()) &&
         t.generics().size() == 1)
       {
         return t.generics().get(0);
diff --git a/tests/reg_issue169_backward_type_propagation_array/Makefile b/tests/reg_issue169_backward_type_propagation_array/Makefile
new file mode 100644
index 000000000..704c75f62
--- /dev/null
+++ b/tests/reg_issue169_backward_type_propagation_array/Makefile
@@ -0,0 +1,27 @@
+# This file is part of the Fuzion language implementation.
+#
+# The Fuzion language implementation is free software: you can redistribute it
+# and/or modify it under the terms of the GNU General Public License as published
+# by the Free Software Foundation, version 3 of the License.
+#
+# The Fuzion language implementation is distributed in the hope that it will be
+# useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License along with The
+# Fuzion language implementation.  If not, see <https://www.gnu.org/licenses/>.
+
+
+# -----------------------------------------------------------------------
+#
+#  Tokiwa Software GmbH, Germany
+#
+#  Source code of Fuzion test Makefile
+#
+#  Author: Fridtjof Siebert (siebert@tokiwa.software)
+#
+# -----------------------------------------------------------------------
+
+override NAME = issue169
+include ../positive.mk
diff --git a/tests/reg_issue169_backward_type_propagation_array/issue169.fz b/tests/reg_issue169_backward_type_propagation_array/issue169.fz
new file mode 100644
index 000000000..b878127a8
--- /dev/null
+++ b/tests/reg_issue169_backward_type_propagation_array/issue169.fz
@@ -0,0 +1,16 @@
+issue169 =>
+
+  a array i32 := []
+  b Sequence i32 := []
+  c Sequence u8 := []
+  d Sequence f32 := [0,1,2]
+  e Sequence (Sequence i16) := [[0,1],[2]]
+  # NYI does not work yet
+  # f := [u8 4, 3, 3]
+
+  say (type_of a)
+  say (type_of b)
+  say (type_of c)
+  say (type_of d)
+  say (type_of e)
+  # say (type_of f)

From 3df243d267dc615157608dd3607d31e954f58541 Mon Sep 17 00:00:00 2001
From: Michael Lill <michael.lill@tokiwa.software>
Date: Fri, 4 Aug 2023 13:09:19 +0200
Subject: [PATCH 2/2] add NYI comment

---
 src/dev/flang/ast/InlineArray.java | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/dev/flang/ast/InlineArray.java b/src/dev/flang/ast/InlineArray.java
index e589ac751..c4ab54049 100644
--- a/src/dev/flang/ast/InlineArray.java
+++ b/src/dev/flang/ast/InlineArray.java
@@ -181,6 +181,7 @@ private AbstractType elementType(AbstractType t)
     if (PRECONDITIONS) require
       (t != null);
 
+    // NYI see issue: #1817
     if (Types.resolved.f_array.inheritsFrom(t.featureOfType()) &&
         t.generics().size() == 1)
       {