Slicing docs + --no-extensions

Author: IvanIsCoding

docs/manual.md

@@ -33,6 +33,9 @@ See the [installation guide](`crate::installation_guide`) for installation instr
 
 ## Overview
 
+<details>
+<summary>celq command line options</summary>
+
 ```none
 A CEL command-line query tool for JSON data
 
@@ -56,12 +59,15 @@ Options:
   -r, --raw-output             If the output is a JSON string, output it raw without quotes
   -S, --sort-keys              Output the fields of each object with the keys in sorted order
   -f, --from-file <FILE>       Read CEL expression from a file
-  -p, --pretty-print
+  -p, --pretty-print           Output JSON with identation and line breaks for human readability
   -g, --greppable              Output in a greppable format (gron style)
+      --no-extensions          Disable extensions and use only standard CEL functions
   -h, --help                   Print help
   -V, --version                Print version
 ```
 
+</details>
+
 ## Quick Start
 
 `celq` reads JSON from the input and lets users process it with CEL:
@@ -137,6 +143,7 @@ This file contains the simplified response from the Yahoo Finance Unofficial JSO
   * [Reading Files](#reading-files)
   * [Writing Files](#writing-files)
   * [Output JSON](#output-json)
+  * [Slicing lists](#slicing-lists)
   * [Reading CEL from a file](#reading-cel-from-a-file)
   * [Dealing with NDJSON](#dealing-with-ndjson)
   * [Slurping](#slurping)
@@ -197,6 +204,19 @@ Notice that by default `celq` does not guarantee the key order of the output. If
 cat yfinance.json | celq --sort-keys '{"symbol": this.chart.result[0].meta.longName, "price": this.chart.result[0].meta.regularMarketPrice}'
 ```
 
+### Slicing lists
+
+`celq` implements the popular slice extension for CEL. For example:
+
+```bash
+echo '["apples", "bananas", "blueberry"]' | celq 'this.slice(1, 3)'
+# Outputs: ["bananas", "blueberry"]
+```
+
+Slicing follows Python conventions: it is 0-indexed and works with negative indices. The `.slice()` calls always requires two arguments. If you need to slice until the end of the list, do `this.slice(pos, size(this.slice))`. Similarly, do `this.slice(0, pos)` to start from the beginning.
+
+If you want to keep your CEL code portable, pass the `--no-extensions` arguments to disable slicing and all other extensions.
+
 ### Reading CEL from a file
 
 In the previous example, the CEL expression for the JSON became long. Let's say we saved the expression in `stock.cel` with the following contents:

src/cli.rs

@@ -150,13 +150,18 @@ pub struct Cli {
     #[arg(short = 'f', long = "from-file", value_name = "FILE")]
     pub from_file: Option<std::path::PathBuf>,
 
+    /// Output JSON with identation and line breaks for human readability
     #[arg(short = 'p', long = "pretty-print")]
     pub pretty_print: bool,
 
     /// Output in a greppable format (gron style)
     #[arg(short = 'g', long = "greppable")]
     pub greppable: bool,
 
+    /// Disable extensions and use only standard CEL functions
+    #[arg(long = "no-extensions")]
+    pub no_extensions: bool,
+
     /// CEL expression to evaluate
     #[arg(value_name = "expr")]
     pub expression: Option<String>,
@@ -190,4 +195,5 @@ pub struct InputParameters {
     pub pretty_print: bool,
     pub raw_output: bool,
     pub greppable: bool,
+    pub no_extensions: bool,
 }

src/input_handler.rs

@@ -175,7 +175,10 @@ fn handle_json(
 ) -> Result<(String, bool)> {
     // Create context with default values
     let mut context = Context::default();
-    context.add_function("slice", slice_extension::slice);
+
+    if !input_params.no_extensions {
+        context.add_function("slice", slice_extension::slice);
+    }
 
     // Add argument variables to context
     for (name, value) in arg_variables {

src/input_handler_test.rs

@@ -15,6 +15,7 @@ fn default_params() -> InputParameters {
         pretty_print: false,
         raw_output: false,
         greppable: false,
+        no_extensions: false,
     }
 }
 

src/main.rs

@@ -91,6 +91,7 @@ fn main() -> io::Result<()> {
         pretty_print: cli.pretty_print,
         raw_output: cli.raw_output,
         greppable: cli.greppable,
+        no_extensions: cli.no_extensions,
     };
 
     match handle_input(&program, &arg_variables, &input_params) {

tests/golden.rs

@@ -917,3 +917,29 @@ fn test_boolean_false_exit_code() -> io::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_slice_fails_without_extensions() -> io::Result<()> {
+    let mut child = process::Command::new(env!("CARGO_BIN_EXE_celq"))
+        .args(["--no-extensions", "this.items.slice(0, 2)"])
+        .stdin(process::Stdio::piped())
+        .stdout(process::Stdio::piped())
+        .stderr(process::Stdio::piped())
+        .spawn()?;
+
+    // Write test input
+    if let Some(mut stdin) = child.stdin.take() {
+        use std::io::Write;
+        stdin.write_all(br#"{"items":[1,2,3,4,5]}"#)?;
+    }
+
+    let output = child.wait_with_output()?;
+
+    // Check that the command failed (non-zero exit code)
+    assert!(
+        !output.status.success(),
+        "Expected command to fail without extensions, but it succeeded"
+    );
+
+    Ok(())
+}