fix(set): Dont crash on bad negative bounds

Fixes #619

Author: epage

src/path/mod.rs

@@ -41,11 +41,13 @@ impl std::fmt::Display for ParseError {
 impl std::error::Error for ParseError {}
 
 /// Convert a relative index into an absolute index
-fn abs_index(index: isize, len: usize) -> Option<usize> {
+fn abs_index(index: isize, len: usize) -> Result<usize, usize> {
     if index >= 0 {
-        Some(index as usize)
+        Ok(index as usize)
+    } else if let Some(index) = len.checked_sub(index.unsigned_abs()) {
+        Ok(index)
     } else {
-        len.checked_sub(index.unsigned_abs())
+        Err((len as isize + index).unsigned_abs())
     }
 }
 
@@ -81,7 +83,7 @@ impl Expression {
             Self::Subscript(expr, index) => match expr.get(root) {
                 Some(value) => match value.kind {
                     ValueKind::Array(ref array) => {
-                        let index = abs_index(index, array.len())?;
+                        let index = abs_index(index, array.len()).ok()?;
                         array.get(index)
                     }
 
@@ -137,7 +139,7 @@ impl Expression {
 
                     match value.kind {
                         ValueKind::Array(ref mut array) => {
-                            let index = abs_index(index, array.len())?;
+                            let index = abs_index(index, array.len()).ok()?;
 
                             if index >= array.len() {
                                 array.resize(index + 1, Value::new(None, ValueKind::Nil));
@@ -212,10 +214,21 @@ impl Expression {
                     }
 
                     if let ValueKind::Array(ref mut array) = parent.kind {
-                        let uindex = abs_index(index, array.len()).unwrap();
-                        if uindex >= array.len() {
-                            array.resize(uindex + 1, Value::new(None, ValueKind::Nil));
-                        }
+                        let uindex = match abs_index(index, array.len()) {
+                            Ok(uindex) => {
+                                if uindex >= array.len() {
+                                    array.resize(uindex + 1, Value::new(None, ValueKind::Nil));
+                                }
+                                uindex
+                            }
+                            Err(insertion) => {
+                                array.splice(
+                                    0..0,
+                                    (0..insertion).map(|_| Value::new(None, ValueKind::Nil)),
+                                );
+                                0
+                            }
+                        };
 
                         array[uindex] = value;
                     }

tests/testsuite/set.rs

@@ -63,7 +63,6 @@ fn test_set_scalar_path() {
 
 #[test]
 #[cfg(feature = "json")]
-#[should_panic]
 fn test_set_arr_path() {
     let config = Config::builder()
         .set_override("present[0].name", "Ivan")