(arrow-rs) branch main updated: fix: Avoid spurious assert when Parquet decimal has scale == precision (#10875)

[jeffreyvo]

This is an automated email from the ASF dual-hosted git repository.

Jefffrey pushed a commit to branch main
in repository https://gitbox.apache.org/repos/asf/arrow-rs.git


The following commit(s) were added to refs/heads/main by this push:
     new 579ccf1a49 fix: Avoid spurious assert when Parquet decimal has scale 
== precision (#10875)
579ccf1a49 is described below

commit 579ccf1a490c991a925c01bb055728e7a2c13f4a
Author: Neil Conway <neil.con...@gmail.com>
AuthorDate: Wed Aug 26 20:29:30 2026 -0400

    fix: Avoid spurious assert when Parquet decimal has scale == precision 
(#10875)
    
    # Which issue does this PR close?
    
    - Closes #10874.
    
    # Rationale for this change
    
    `convert_decimal_to_string` asserted `precision > scale`, but the
    Parquet spec requires only `scale <= precision`, so displaying a row
    from a file with a `DECIMAL(p, p)` column resulted in a spurious
    assertion failure.
    
    # What changes are included in this PR?
    
    * Weaken assert to match Parquet spec
    * Update test coverage
    
    # Are these changes tested?
    
    Yes, test coverage added.
    
    # Are there any user-facing changes?
    
    No.
---
 parquet/src/record/api.rs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/parquet/src/record/api.rs b/parquet/src/record/api.rs
index 3a09f5253c..665a54edb1 100644
--- a/parquet/src/record/api.rs
+++ b/parquet/src/record/api.rs
@@ -990,11 +990,11 @@ fn convert_time_micros_to_string(value: i64) -> String {
 }
 
 /// Helper method to convert Parquet decimal into a string.
-/// We assert that `scale >= 0` and `precision > scale`, but this will be 
enforced
-/// when constructing Parquet schema.
+/// We assert that `scale >= 0` and `precision >= scale`, which is enforced 
when
+/// constructing a Parquet schema.
 #[inline]
 fn convert_decimal_to_string(decimal: &Decimal) -> String {
-    assert!(decimal.scale() >= 0 && decimal.precision() > decimal.scale());
+    assert!(decimal.scale() >= 0 && decimal.precision() >= decimal.scale());
 
     // Specify as signed bytes to resolve sign as part of conversion.
     let num = BigInt::from_signed_bytes_be(decimal.data());
@@ -1428,6 +1428,9 @@ mod tests {
         check_decimal(vec![0, 0, 0, 0, 1, 201, 195, 140], 18, 2, "300000.12");
         check_decimal(vec![207, 200], 10, 2, "-123.44");
         check_decimal(vec![207, 200], 10, 8, "-0.00012344");
+        check_decimal(vec![48, 57], 5, 5, "0.12345");
+        check_decimal(vec![207, 199], 5, 5, "-0.12345");
+        check_decimal(vec![45], 5, 5, "0.00045");
     }
 
     #[test]