sdf-jkl commented on code in PR #11961:
URL: https://github.com/apache/arrow-rs/pull/11961#discussion_r4413119590
##########
parquet-variant/src/variant/metadata.rs:
##########
@@ -32,9 +32,13 @@ pub(crate) struct VariantMetadataHeader {
offset_size: OffsetSizeBytes,
}
-// According to the spec this is currently always = 1, and so we store this
const for validation
-// purposes and to make that visible.
-const CORRECT_VERSION_VALUE: u8 = 1;
+/// The version of the Variant specification implemented by this crate.
+///
+/// The spec currently defines only version 1. It appears in two places on
+/// disk: the 4-bit version field of every metadata header, and the
+/// `specification_version` of the Parquet `VARIANT` logical type annotation.
+/// Both must carry this value.
+pub const VARIANT_SPEC_VERSION: u8 = 1;
Review Comment:
`WritableMetadataBuilder::finish` still writes `0x01`, and
`EMPTY_VARIANT_METADATA_BYTES` still starts with a literal `1`.
Suggested changes:
```diff
diff --git a/parquet-variant/src/builder/metadata.rs
b/parquet-variant/src/builder/metadata.rs
--- a/parquet-variant/src/builder/metadata.rs
+++ b/parquet-variant/src/builder/metadata.rs
@@ -23,1 +23,1 @@
-use crate::{VariantMetadata, int_size};
+use crate::{VARIANT_SPEC_VERSION, VariantMetadata, int_size};
@@ -231,1 +231,3 @@
- metadata_buffer.push(0x01 | ((is_sorted as u8) << 4) |
((offset_size - 1) << 6));
+ metadata_buffer.push(
+ VARIANT_SPEC_VERSION | ((is_sorted as u8) << 4) | ((offset_size
- 1) << 6),
+ );
diff --git a/parquet-variant/src/variant/metadata.rs
b/parquet-variant/src/variant/metadata.rs
--- a/parquet-variant/src/variant/metadata.rs
+++ b/parquet-variant/src/variant/metadata.rs
@@ -162,1 +162,1 @@
-pub const EMPTY_VARIANT_METADATA_BYTES: &[u8] = &[1, 0, 0];
+pub const EMPTY_VARIANT_METADATA_BYTES: &[u8] = &[VARIANT_SPEC_VERSION, 0,
0];
```
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