Allow values from SourceClass inside rust Source

Inside ViewTest::testOnTouchEventScroll, some MotionEvents are created
without a valid source. During injection, they get appended with
SourceClass::Pointer.

If these events are sent into the InputVerifier, it's basically being
asked to convert 0x2 === AINPUT_SOURCE_CLASS_POINTER into rust's
input::Source.

This fails during unwrap:

$ TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
[ RUN      ] InputVerifierTest.BadSourceProcess
thread '<unnamed>' panicked at 'called `Option::unwrap()` on a `None` value', frameworks/native/libs/input/rust/lib.rs:84:35
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5
Aborted

To mitigate this, add the SourceClass definitions into Source, thus
allowing such conversions.

Bug: 303143553
Bug: 211379801
Test: TEST=libinput_rust_test; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Test: TEST=libinput_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I46415d88251937959104bb82a3976e72ffcfcaf9
diff --git a/libs/input/rust/input.rs b/libs/input/rust/input.rs
index 9725b00..804f96d 100644
--- a/libs/input/rust/input.rs
+++ b/libs/input/rust/input.rs
@@ -35,7 +35,20 @@
 
 bitflags! {
     /// Source of the input device or input events.
+    #[derive(Debug, PartialEq)]
     pub struct Source: u32 {
+        // Constants from SourceClass, added here for compatibility reasons
+        /// SourceClass::Button
+        const SourceClassButton = SourceClass::Button as u32;
+        /// SourceClass::Pointer
+        const SourceClassPointer = SourceClass::Pointer as u32;
+        /// SourceClass::Navigation
+        const SourceClassNavigation = SourceClass::Navigation as u32;
+        /// SourceClass::Position
+        const SourceClassPosition = SourceClass::Position as u32;
+        /// SourceClass::Joystick
+        const SourceClassJoystick = SourceClass::Joystick as u32;
+
         /// SOURCE_UNKNOWN
         const Unknown = input_bindgen::AINPUT_SOURCE_UNKNOWN;
         /// SOURCE_KEYBOARD
@@ -190,3 +203,14 @@
         self.bits() & class_bits == class_bits
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::input::SourceClass;
+    use crate::Source;
+    #[test]
+    fn convert_source_class_pointer() {
+        let source = Source::from_bits(input_bindgen::AINPUT_SOURCE_CLASS_POINTER).unwrap();
+        assert!(source.is_from_class(SourceClass::Pointer));
+    }
+}