Fix FFI crash when embedded struct/union is skipped.

visit_struct and visit_union pushed nil into version arrays when
recursive calls returned nil (skipped, forward-declared, or opaque).
This caused NoMethodError in merge_children when the nil shared a
versioned bucket with non-nil entries.

Author: cfis

lib/ruby-bindgen/generators/ffi/ffi.rb

@@ -240,14 +240,18 @@ def visit_struct(cursor)
 
         # Define any embedded structures
         cursor.find_by_kind(false, :cursor_struct).each do |struct|
+          content = visit_struct(struct)
+          next unless content
           version = @symbols.version(struct)
-          result[version] << visit_struct(struct)
+          result[version] << content
         end
 
         # Define any embedded unions
         cursor.find_by_kind(false, :cursor_union).each do |union|
+          content = visit_union(union)
+          next unless content
           version = @symbols.version(union)
-          result[version] << visit_union(union)
+          result[version] << content
         end
 
         # Define any embedded callbacks
@@ -311,14 +315,18 @@ def visit_union(cursor)
 
         # Define any embedded unions
         cursor.find_by_kind(false, :cursor_union).each do |union|
+          content = visit_union(union)
+          next unless content
           version = @symbols.version(union)
-          result[version] << visit_union(union)
+          result[version] << content
         end
 
         # Define any embedded structures
         cursor.find_by_kind(false, :cursor_struct).each do |struct|
+          content = visit_struct(struct)
+          next unless content
           version = @symbols.version(struct)
-          result[version] << visit_struct(struct)
+          result[version] << content
         end
 
         # Define any embedded callbacks

test/bindings/c/filtering.rb

@@ -15,4 +15,9 @@ class IncludedStruct < FFI::Struct
   )
 
   typedef :int, :included_typedef
+
+  class ContainerStruct < FFI::Struct
+    layout :member, SkippedEmbedded,
+           :value, :int
+  end
 end

test/ffi_test.rb

@@ -60,7 +60,8 @@ def test_filtering
                         "/internal_helper.*/",
                         "SkippedStruct",
                         "SkippedEnum",
-                        "SkippedTypedef"] })
+                        "SkippedTypedef",
+                        "SkippedEmbedded"] })
   end
 
   def test_rename

test/headers/c/filtering.h

@@ -69,3 +69,15 @@ typedef int SkippedTypedef;
 
 // Normal typedef - should be INCLUDED
 typedef int IncludedTypedef;
+
+// --- Embedded skipped struct ---
+
+// Struct containing an embedded struct that is skipped
+struct ContainerStruct
+{
+    struct SkippedEmbedded
+    {
+        int a;
+    } member;
+    int value;
+};