feat: per value support for fixed-length packed structs

rust/lance-encoding/src/compression.rs

@@ -49,6 +49,7 @@ use crate::{
             },
             general::{GeneralMiniBlockCompressor, GeneralMiniBlockDecompressor},
             packed::{
+                PackedStructFixedPerValueDecompressor, PackedStructFixedPerValueEncoder,
                 PackedStructFixedWidthMiniBlockDecompressor,
                 PackedStructFixedWidthMiniBlockEncoder, PackedStructVariablePerValueDecompressor,
                 PackedStructVariablePerValueEncoder, VariablePackedStructFieldDecoder,
@@ -770,9 +771,9 @@ impl CompressionStrategy for DefaultCompressionStrategy {
                         field.children.clone(),
                     )))
                 } else {
-                    Err(Error::invalid_input(
-                        "Packed struct per-value compression should not be used for fixed-width-only structs",
-                    ))
+                    Ok(Box::new(PackedStructFixedPerValueEncoder::new(
+                        field.children.clone(),
+                    )))
                 }
             }
             DataBlock::VariableWidth(variable_width) => {
@@ -1043,6 +1044,9 @@ impl DecompressionStrategy for DefaultDecompressionStrategy {
             ))),
             Compression::Flat(flat) => Ok(Box::new(ValueDecompressor::from_flat(flat))),
             Compression::FixedSizeList(fsl) => Ok(Box::new(ValueDecompressor::from_fsl(fsl))),
+            Compression::PackedStruct(description) => Ok(Box::new(
+                PackedStructFixedPerValueDecompressor::new(description)?,
+            )),
             _ => todo!("fixed-per-value decompressor for {:?}", description),
         }
     }

rust/lance-encoding/src/encodings/logical/primitive.rs

@@ -5463,14 +5463,6 @@ impl PrimitiveStructuralEncoder {
                         variable.bits_per_offset
                     ))
                 }
-                DataBlock::Struct(struct_data_block)
-                    if !struct_data_block.has_variable_width_child() =>
-                {
-                    Some(
-                        "Full-zip packed struct requires at least one variable-width child"
-                            .to_string(),
-                    )
-                }
                 DataBlock::Dictionary(_) => {
                     Some("Full-zip does not encode dictionary data blocks directly".to_string())
                 }