fix: Raise on oob decimal precision (#17445)

pola-rs · Jul 5, 2024 · a539d88 · a539d88
1 parent 221bea8
commit a539d88
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Showing 3 changed files with 18 additions and 6 deletions.
diff --git a/crates/polars-core/src/chunked_array/cast.rs b/crates/polars-core/src/chunked_array/cast.rs
@@ -51,7 +51,7 @@ pub(crate) fn cast_chunks(
     let check_nulls = matches!(options, CastOptions::Strict);
     let options = options.into();
 
-    let arrow_dtype = dtype.to_arrow(true);
+    let arrow_dtype = dtype.try_to_arrow(true)?;
     chunks
         .iter()
         .map(|arr| {

diff --git a/crates/polars-core/src/datatypes/dtype.rs b/crates/polars-core/src/datatypes/dtype.rs
@@ -55,6 +55,7 @@ pub enum DataType {
     Float64,
     /// Fixed point decimal type optional precision and non-negative scale.
     /// This is backed by a signed 128-bit integer which allows for up to 38 significant digits.
+    /// Meaning max precision is 38.
     #[cfg(feature = "dtype-decimal")]
     Decimal(Option<usize>, Option<usize>), // precision/scale; scale being None means "infer"
     /// String data
@@ -542,11 +543,15 @@ impl DataType {
             Float32 => Ok(ArrowDataType::Float32),
             Float64 => Ok(ArrowDataType::Float64),
             #[cfg(feature = "dtype-decimal")]
-            // note: what else can we do here other than setting precision to 38?..
-            Decimal(precision, scale) => Ok(ArrowDataType::Decimal(
-                (*precision).unwrap_or(38),
-                scale.unwrap_or(0), // and what else can we do here?
-            )),
+            Decimal(precision, scale) => {
+                let precision = (*precision).unwrap_or(38);
+                polars_ensure!(precision <= 38 && precision > 0, InvalidOperation: "decimal precision should be <= 38 & >= 1");
+
+                Ok(ArrowDataType::Decimal(
+                    precision,
+                    scale.unwrap_or(0), // and what else can we do here?
+                ))
+            },
             String => {
                 let dt = if pl_flavor {
                     ArrowDataType::Utf8View

diff --git a/py-polars/tests/unit/datatypes/test_decimal.py b/py-polars/tests/unit/datatypes/test_decimal.py
@@ -472,3 +472,10 @@ def test_decimal_supertype() -> None:
         pl.col("column_0").cast(pl.Decimal(scale=6)) * 1
     )
     assert q.collect().dtypes[0].is_decimal()
+
+
+def test_decimal_raise_oob_precision() -> None:
+    df = pl.DataFrame({"a": [1.0]})
+    # max precision is 38.
+    with pytest.raises(pl.exceptions.InvalidOperationError):
+        df.select(b=pl.col("a").cast(pl.Decimal(76, 38)))