martin-g commented on code in PR #19805:
URL: https://github.com/apache/datafusion/pull/19805#discussion_r2693483206
##########
datafusion/spark/src/function/string/mod.rs:
##########
@@ -90,6 +92,11 @@ pub mod expr_fn {
strfmt args
));
export_functions!((space, "Returns a string consisting of n spaces.",
arg1));
+ export_functions!((
+ substring,
+ "Returns the substring from string str starting at position pos with
length len.",
+ str pos
Review Comment:
```suggestion
str pos len
```
?!
##########
datafusion/spark/src/function/string/substring.rs:
##########
@@ -0,0 +1,284 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use arrow::array::{
+ Array, ArrayRef, AsArray, GenericStringBuilder, Int64Array,
StringArrayType,
+ StringViewArray, StringViewBuilder,
+};
+use arrow::datatypes::DataType;
+use datafusion_common::arrow::datatypes::{Field, FieldRef};
+use datafusion_common::cast::as_int64_array;
+use datafusion_common::types::{
+ NativeType, logical_int32, logical_int64, logical_string,
+};
+use datafusion_common::{Result, exec_err};
+use datafusion_expr::{Coercion, ReturnFieldArgs, TypeSignatureClass};
+use datafusion_expr::{
+ ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, Signature, TypeSignature,
+ Volatility,
+};
+use datafusion_functions::unicode::substr::{enable_ascii_fast_path,
get_true_start_end};
+use datafusion_functions::utils::make_scalar_function;
+use std::any::Any;
+use std::sync::Arc;
+
+/// Spark-compatible `substring` expression
+/// <https://spark.apache.org/docs/latest/api/sql/index.html#substring>
+///
+/// Returns the substring from string starting at position pos with length len.
+/// Position is 1-indexed. If pos is negative, it counts from the end of the
string.
+/// Returns NULL if any input is NULL.
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub struct SparkSubstring {
+ signature: Signature,
+ aliases: Vec<String>,
+}
+
+impl Default for SparkSubstring {
+ fn default() -> Self {
+ Self::new()
+ }
+}
+
+impl SparkSubstring {
+ pub fn new() -> Self {
+ let string =
Coercion::new_exact(TypeSignatureClass::Native(logical_string()));
+ let int64 = Coercion::new_implicit(
+ TypeSignatureClass::Native(logical_int64()),
+ vec![TypeSignatureClass::Native(logical_int32())],
+ NativeType::Int64,
+ );
+ Self {
+ signature: Signature::one_of(
+ vec![
+ TypeSignature::Coercible(vec![string.clone(),
int64.clone()]),
+ TypeSignature::Coercible(vec![
+ string.clone(),
+ int64.clone(),
+ int64.clone(),
+ ]),
+ ],
+ Volatility::Immutable,
+ )
+ .with_parameter_names(vec![
+ "str".to_string(),
+ "pos".to_string(),
+ "length".to_string(),
+ ])
+ .expect("valid parameter names"),
+ aliases: vec![String::from("substr")],
+ }
+ }
+}
+
+impl ScalarUDFImpl for SparkSubstring {
+ fn as_any(&self) -> &dyn Any {
+ self
+ }
+
+ fn name(&self) -> &str {
+ "substring"
+ }
+
+ fn signature(&self) -> &Signature {
+ &self.signature
+ }
+
+ fn aliases(&self) -> &[String] {
+ &self.aliases
+ }
+
+ fn invoke_with_args(&self, args: ScalarFunctionArgs) ->
Result<ColumnarValue> {
+ make_scalar_function(spark_substring, vec![])(&args.args)
+ }
+
+ fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
+ datafusion_common::internal_err!(
+ "return_type should not be called for Spark substr"
+ )
+ }
+
+ fn return_field_from_args(&self, args: ReturnFieldArgs<'_>) ->
Result<FieldRef> {
+ // Spark semantics: substr returns NULL if ANY input is NULL
+ let nullable = args.arg_fields.iter().any(|f| f.is_nullable());
+
+ Ok(Arc::new(Field::new(
+ "substring",
+ args.arg_fields[0].data_type().clone(),
+ nullable,
+ )))
+ }
+}
+
+fn spark_substring(args: &[ArrayRef]) -> Result<ArrayRef> {
+ let start_array = as_int64_array(&args[1])?;
+ let length_array = if args.len() > 2 {
+ Some(as_int64_array(&args[2])?)
+ } else {
+ None
+ };
+
+ match args[0].data_type() {
+ DataType::Utf8 => spark_substring_utf8::<i32, _>(
+ &args[0].as_string::<i32>(),
+ start_array,
+ length_array,
+ ),
+ DataType::LargeUtf8 => spark_substring_utf8::<i64, _>(
+ &args[0].as_string::<i64>(),
+ start_array,
+ length_array,
+ ),
+ DataType::Utf8View => {
+ spark_substring_view(args[0].as_string_view(), start_array,
length_array)
+ }
+ other => exec_err!(
+ "Unsupported data type {other:?} for function spark_substring,
expected Utf8View, Utf8 or LargeUtf8."
+ ),
+ }
+}
+
+/// Convert Spark's start position to DataFusion's 1-based start position.
+///
+/// Spark semantics:
+/// - Positive start: 1-based index from beginning
+/// - Zero start: treated as 1
+/// - Negative start: counts from end of string
+///
+/// Returns the converted 1-based start position for use with
`get_true_start_end`.
+#[inline]
+fn spark_start_to_datafusion_start(start: i64, len: usize) -> i64 {
+ if start >= 0 {
+ start.max(1)
+ } else {
+ let start = start + len as i64 + 1;
Review Comment:
Imaginary, but possible input:
```rust
fn main() {
// input
let start = -1_i64;
let len = 1_u64 + i64::MAX as u64;
// the tested logic
let start = start + len as i64 + 1;
println!("len: {len}\nstart: {start}");
}
```
fails with:
```
thread 'main' (40) panicked at src/main.rs:6:17:
attempt to add with overflow
```
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