Add padding size calculation to DekuSize

wcampbell0x2a · wcampbell0x2a · commit 66bc051796ba · 2026-01-15T00:44:06.000-05:00
diff --git a/deku-derive/src/macros/deku_size.rs b/deku-derive/src/macros/deku_size.rs
@@ -36,6 +36,21 @@ fn calculate_fields_size<'a>(
             components.push(quote! { #magic_size });
         }
 
+        #[cfg(feature = "bits")]
+        {
+            if let Some(pad_before) =
+                calculate_padding_size(f.pad_bits_before.as_ref(), f.pad_bytes_before.as_ref())
+            {
+                components.push(pad_before);
+            }
+        }
+        #[cfg(not(feature = "bits"))]
+        {
+            if let Some(pad_before) = calculate_padding_size(f.pad_bytes_before.as_ref()) {
+                components.push(pad_before);
+            }
+        }
+
         let field_type = &f.ty;
         #[cfg(feature = "bits")]
         if let Some(bits) = &f.bits {
@@ -53,6 +68,21 @@ fn calculate_fields_size<'a>(
             components.push(quote! { <#field_type as ::#crate_::DekuSize>::SIZE_BITS });
         }
 
+        #[cfg(feature = "bits")]
+        {
+            if let Some(pad_after) =
+                calculate_padding_size(f.pad_bits_after.as_ref(), f.pad_bytes_after.as_ref())
+            {
+                components.push(pad_after);
+            }
+        }
+        #[cfg(not(feature = "bits"))]
+        {
+            if let Some(pad_after) = calculate_padding_size(f.pad_bytes_after.as_ref()) {
+                components.push(pad_after);
+            }
+        }
+
         if components.is_empty() {
             None
         } else {
@@ -85,6 +115,29 @@ fn calculate_magic_size(magic: &syn::LitByteStr) -> TokenStream {
     quote! { #magic_len * 8 }
 }
 
+/// Calculate padding size (with bits feature)
+#[cfg(feature = "bits")]
+fn calculate_padding_size(
+    pad_bits: Option<&TokenStream>,
+    pad_bytes: Option<&TokenStream>,
+) -> Option<TokenStream> {
+    match (pad_bits, pad_bytes) {
+        (Some(bits), Some(bytes)) => Some(quote! { (#bits) + ((#bytes) * 8) }),
+        (Some(bits), None) => Some(quote! { (#bits) }),
+        (None, Some(bytes)) => Some(quote! { ((#bytes) * 8) }),
+        (None, None) => None,
+    }
+}
+
+/// Calculate padding size (without bits feature)
+#[cfg(not(feature = "bits"))]
+fn calculate_padding_size(pad_bytes: Option<&TokenStream>) -> Option<TokenStream> {
+    match pad_bytes {
+        Some(bytes) => Some(quote! { ((#bytes) * 8) }),
+        None => None,
+    }
+}
+
 /// Add DekuSize trait bounds to where clause for fields that need them
 fn add_field_bounds<'a>(
     where_clause: &mut Option<syn::WhereClause>,
diff --git a/tests/test_size.rs b/tests/test_size.rs
@@ -562,3 +562,118 @@ fn test_nested_struct_with_magic() {
     assert_eq!(InnerWithMagic::SIZE_BYTES, Some(4));
     assert_eq!(OuterWithMagic::SIZE_BYTES, Some(8));
 }
+
+#[test]
+fn test_struct_with_pad_bytes_before() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    struct PadBeforeStruct {
+        field_a: u8,
+        #[deku(pad_bytes_before = "2")]
+        field_b: u8,
+    }
+
+    assert_eq!(PadBeforeStruct::SIZE_BYTES, Some(4));
+    assert_eq!(PadBeforeStruct::SIZE_BITS, 32);
+}
+
+#[test]
+fn test_struct_with_pad_bytes_after() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    struct PadAfterStruct {
+        #[deku(pad_bytes_after = "3")]
+        field_a: u8,
+        field_b: u8,
+    }
+
+    assert_eq!(PadAfterStruct::SIZE_BYTES, Some(5));
+    assert_eq!(PadAfterStruct::SIZE_BITS, 40);
+}
+
+#[test]
+fn test_struct_with_pad_bytes_before_and_after() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    struct PadBothStruct {
+        #[deku(pad_bytes_before = "1", pad_bytes_after = "2")]
+        field_a: u8,
+        field_b: u16,
+    }
+
+    assert_eq!(PadBothStruct::SIZE_BYTES, Some(6));
+    assert_eq!(PadBothStruct::SIZE_BITS, 48);
+}
+
+#[test]
+#[cfg(feature = "bits")]
+fn test_struct_with_pad_bits_before() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    #[deku(endian = "big")]
+    struct PadBitsBefore {
+        #[deku(bits = 4)]
+        field_a: u8,
+        #[deku(pad_bits_before = "4")]
+        #[deku(bits = 4)]
+        field_b: u8,
+    }
+
+    assert_eq!(PadBitsBefore::SIZE_BITS, 12);
+    assert_eq!(PadBitsBefore::SIZE_BYTES, None);
+}
+
+#[test]
+#[cfg(feature = "bits")]
+fn test_struct_with_pad_bits_after() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    #[deku(endian = "big")]
+    struct PadBitsAfter {
+        #[deku(bits = 3, pad_bits_after = "5")]
+        field_a: u8,
+        field_b: u8,
+    }
+
+    assert_eq!(PadBitsAfter::SIZE_BITS, 16);
+    assert_eq!(PadBitsAfter::SIZE_BYTES, Some(2));
+}
+
+#[test]
+#[cfg(feature = "bits")]
+fn test_struct_with_mixed_padding() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    #[deku(endian = "big")]
+    struct MixedPadding {
+        #[deku(pad_bits_before = "2", pad_bytes_before = "1")]
+        #[deku(bits = 6)]
+        field_a: u8,
+        field_b: u8,
+    }
+
+    assert_eq!(MixedPadding::SIZE_BITS, 24);
+    assert_eq!(MixedPadding::SIZE_BYTES, Some(3));
+}
+
+#[test]
+fn test_struct_without_padding() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    struct NoPaddingStruct {
+        field_a: u8,
+        field_b: u16,
+    }
+
+    assert_eq!(NoPaddingStruct::SIZE_BYTES, Some(3));
+    assert_eq!(NoPaddingStruct::SIZE_BITS, 24);
+}
+
+#[test]
+fn test_multiple_fields_with_padding() {
+    #[derive(DekuRead, DekuWrite, DekuSize)]
+    struct MultiplePadding {
+        #[deku(pad_bytes_before = "1")]
+        field_a: u8,
+        #[deku(pad_bytes_after = "2")]
+        field_b: u8,
+        #[deku(pad_bytes_before = "1", pad_bytes_after = "1")]
+        field_c: u8,
+    }
+
+    assert_eq!(MultiplePadding::SIZE_BYTES, Some(8));
+    assert_eq!(MultiplePadding::SIZE_BITS, 64);
+}
