Fix using gl_VertexIndex and gl_InstanceIndex producing errors

vulkano-shaders/src/lib.rs

@@ -176,6 +176,10 @@ fn write_entry_point(doc: &parse::Spirv, instruction: &parse::Instruction) -> St
                                     storage_class: enums::StorageClass::StorageClassInput, .. }
                                     if &result_id == interface =>
                         {
+                            if is_builtin(doc, result_id) {
+                                continue;
+                            }
+
                             input_types.push(type_from_id(doc, result_type_id));
                             let name = name_from_id(doc, result_id);
                             let loc = match location_decoration(doc, result_id) {
@@ -375,6 +379,23 @@ fn location_decoration(doc: &parse::Spirv, searched: u32) -> Option<u32> {
     }).next()
 }
 
+/// Returns true if a `BuiltIn` decorator is applied on an id.
+fn is_builtin(doc: &parse::Spirv, id: u32) -> bool {
+    for instruction in &doc.instructions {
+        match *instruction {
+            parse::Instruction::Decorate { target_id,
+                                           decoration: enums::Decoration::DecorationBuiltIn,
+                                           .. } if target_id == id =>
+            {
+                return true;
+            },
+            _ => ()
+        }
+    }
+
+    false
+}
+
 /// Returns the name of the Vulkan something that corresponds to an `OpCapability`.
 ///
 /// Returns `None` if irrelevant.

vulkano-shaders/src/structs.rs

@@ -91,8 +91,6 @@ fn write_struct(doc: &parse::Spirv, struct_id: u32, members: &[u32]) -> String {
 
 /// Returns true if a `BuiltIn` decorator is applied on a struct member.
 fn is_builtin_member(doc: &parse::Spirv, id: u32, member_id: u32) -> bool {
-    let mut result = String::new();
-
     for instruction in &doc.instructions {
         match *instruction {
             parse::Instruction::MemberDecorate { target_id, member,