[vala/wip/issue/894: 44/45] vala: Automatically remove superfluous silent casts

[Rico Tzschichholz <ricotz src gnome org>]

commit 9788c71ff23ff9ec7452f234d3ca9214a44515d5
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Tue Aug 11 15:22:21 2020 +0200

    vala: Automatically remove superfluous silent casts
    
    If type of expression is target type then omit this GType cast.
    
    This will clean up existing sources which matches the expected scheme for
    type narrowing, see https://gitlab.gnome.org/GNOME/vala/issues/894

 tests/Makefile.am                 |  1 +
 tests/objects/casting-silent.vala | 28 ++++++++++++++++++++++++++++
 vala/valacastexpression.vala      |  9 +++++++++
 3 files changed, 38 insertions(+)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index d6b85de3d..ca85ba0c0 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -390,6 +390,7 @@ TESTS = \
        delegates/bug761360.vala \
        delegates/bug772204.test \
        delegates/bug792077.vala \
+       objects/casting-silent.vala \
        objects/chainup.vala \
        objects/class-ccode-cprefix.vala \
        objects/class_only.vala \
diff --git a/tests/objects/casting-silent.vala b/tests/objects/casting-silent.vala
new file mode 100644
index 000000000..51928cd75
--- /dev/null
+++ b/tests/objects/casting-silent.vala
@@ -0,0 +1,28 @@
+class Foo {
+}
+
+class Bar : Foo {
+}
+
+Bar get_bar () {
+       return new Bar ();
+}
+
+void main() {
+       {
+               var bar = new Foo ();
+               var foo = bar as Foo;
+
+               assert (foo == bar);
+               assert (foo == (bar as Foo));
+               assert (bar == (foo as Foo));
+       }
+       {
+               var bar = get_bar () as Foo;
+               var foo = bar as Bar;
+
+               assert (foo == bar);
+               assert (foo == (bar as Bar));
+               assert (bar == (foo as Foo));
+       }
+}
diff --git a/vala/valacastexpression.vala b/vala/valacastexpression.vala
index 86b9f9a12..e391b5f92 100644
--- a/vala/valacastexpression.vala
+++ b/vala/valacastexpression.vala
@@ -199,6 +199,15 @@ public class Vala.CastExpression : Expression {
 
                if (is_silent_cast) {
                        value_type.nullable = true;
+
+                       // Drop superfluous casts, if the source and target type matches then this cast is 
not required
+                       if (context.profile == Profile.GOBJECT
+                           && type_reference.type_symbol is ObjectTypeSymbol && type_reference.type_symbol 
== inner.value_type.type_symbol) {
+                               Report.warning (source_reference, "Casting to `%s' is superfluous".printf 
(type_reference.to_qualified_string ()));
+                               context.analyzer.replaced_nodes.add (this);
+                               parent_node.replace_expression (this, inner);
+                               return !error;
+                       }
                }
 
                if (context.profile == Profile.GOBJECT