Add slice extension

Author: IvanIsCoding

src/input_handler.rs

@@ -15,6 +15,7 @@ use std::io::{self};
 use crate::InputParameters;
 use crate::cel_value_to_json_value;
 use crate::json_to_cel_variables;
+use crate::slice_extension;
 
 /// Process input from stdin and execute the CEL program
 ///
@@ -174,6 +175,7 @@ fn handle_json(
 ) -> Result<(String, bool)> {
     // Create context with default values
     let mut context = Context::default();
+    context.add_function("slice", slice_extension::slice);
 
     // Add argument variables to context
     for (name, value) in arg_variables {

src/main.rs

@@ -13,6 +13,7 @@ mod cel2json;
 mod cli;
 mod input_handler;
 mod json2cel;
+pub mod slice_extension;
 
 use args2cel::args_to_cel_variables;
 pub use cel2json::cel_value_to_json_value;

src/slice_extension.rs

@@ -0,0 +1,30 @@
+use cel::Value;
+use cel::extractors::This;
+use std::sync::Arc;
+
+/// Returns a slice of a list, Python-style. We support negative indices and indices
+/// that are beyond the end of the list.
+pub fn slice(This(this): This<Arc<Vec<Value>>>, start: i64, end: i64) -> Arc<Vec<Value>> {
+    let len = this.len() as i64;
+
+    // Normalize negative indices
+    let norm_start = if start < 0 {
+        (len + start).max(0)
+    } else {
+        start.min(len)
+    } as usize;
+
+    let norm_end = if end < 0 {
+        (len + end).max(0)
+    } else {
+        end.min(len)
+    } as usize;
+
+    // Handle case where start >= end
+    if norm_start >= norm_end {
+        return Arc::new(Vec::new());
+    }
+
+    // Extract the slice
+    Arc::new(this[norm_start..norm_end].to_vec())
+}

tests/golden.rs

@@ -857,6 +857,42 @@ json.a.b.c.d[0].e = "deep";
     r#"{"a":{"b":{"c":{"d":[{"e":"deep"}]}}}}"#
 );
 
+// Slice extension tests
+test!(
+    slice_basic,
+    &["this.items.slice(1, 3)"],
+    r#"{"items":[1,2,3,4,5]}"#,
+    "[2,3]"
+);
+
+test!(
+    slice_negative_indices,
+    &["this.items.slice(-3, -1)"],
+    r#"{"items":[10,20,30,40,50]}"#,
+    "[30,40]"
+);
+
+test!(
+    slice_from_start,
+    &["this.items.slice(0, 2)"],
+    r#"{"items":["a","b","c","d"]}"#,
+    r#"["a","b"]"#
+);
+
+test!(
+    slice_beyond_bounds,
+    &["this.items.slice(2, 100)"],
+    r#"{"items":[1,2,3]}"#,
+    "[3]"
+);
+
+test!(
+    slice_negative_to_positive,
+    &["this.items.slice(-5, 4)"],
+    r#"{"items":[5,10,15,20,25,30]}"#,
+    "[10,15,20]"
+);
+
 #[test]
 fn test_boolean_false_exit_code() -> io::Result<()> {
     let mut child = process::Command::new(env!("CARGO_BIN_EXE_celq"))