[vala/0.40] codegen: Use result value of assignment rather than its computation

[Rico Tzschichholz <ricotz src gnome org>]

commit 8edce88b72a766242273e62e3963f45777d767ec
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Tue Jan 14 08:36:26 2020 +0100

    codegen: Use result value of assignment rather than its computation
    
    An inline assignment of an array-length, like
    
        int j = --i.length;
    
    resulted in a faulty tranformation
    
        i_length1 = i_length1 - 1;
        j = i_length1 - 1;
    
    Regression of 80d4bf61e0c3100c839f3fdbcb5218996b6afd5f
    
    Fixes https://gitlab.gnome.org/GNOME/vala/issues/895

 codegen/valaccodeassignmentmodule.vala     |  2 +-
 tests/Makefile.am                          |  1 +
 tests/arrays/length-inline-assignment.vala | 29 +++++++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)
---
diff --git a/codegen/valaccodeassignmentmodule.vala b/codegen/valaccodeassignmentmodule.vala
index 1b68b3764..07faaa13a 100644
--- a/codegen/valaccodeassignmentmodule.vala
+++ b/codegen/valaccodeassignmentmodule.vala
@@ -71,7 +71,7 @@ public class Vala.CCodeAssignmentModule : CCodeMemberAccessModule {
                if (assignment.left.value_type is ArrayType && (((ArrayType) 
assignment.left.value_type).inline_allocated)) {
                        return load_variable (variable, assignment.left.target_value);
                } else {
-                       return assignment.right.target_value;
+                       return assignment.left.target_value;
                }
        }
 
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2fb048652..a5471f9fc 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -69,6 +69,7 @@ TESTS = \
        arrays/fixed-length-concat-invalid.test \
        arrays/fixed-length-non-const.test \
        arrays/fixed-length-resize-invalid.test \
+       arrays/length-inline-assignment.vala \
        arrays/struct-field-length-cname.vala \
        arrays/slice-invalid-start.test \
        arrays/slice-invalid-stop.test \
diff --git a/tests/arrays/length-inline-assignment.vala b/tests/arrays/length-inline-assignment.vala
new file mode 100644
index 000000000..baf33055d
--- /dev/null
+++ b/tests/arrays/length-inline-assignment.vala
@@ -0,0 +1,29 @@
+void main () {
+       {
+               int[] i = { 23, 42 };
+               int j = --i.length;
+               assert (i.length == 1);
+               assert (j == 1);
+               j = ++i.length;
+               assert (i.length == 2);
+               assert (j == 2);
+       }
+       {
+               int[] i = { 23, 42 };
+               int j = (i.length = i.length - 1);
+               assert (i.length == 1);
+               assert (j == 1);
+               j = (i.length = i.length + 1);
+               assert (i.length == 2);
+               assert (j == 2);
+       }
+       {
+               int[] i = { 23, 42 };
+               int j = i.length--;
+               assert (i.length == 1);
+               assert (j == 2);
+               j = i.length++;
+               assert (i.length == 2);
+               assert (j == 1);
+       }
+}