Improve errors on invalid ranges in .read

core/src/main/kotlin/eu/iamgio/quarkdown/function/value/data/Range.kt

@@ -53,6 +53,30 @@ data class Range(val start: Int?, val end: Int?) : Iterable<NumberValue> {
             .iterator()
     }
 
+    /**
+     * @param bounds range to check if this range is in. Both its `start` and `end` values must be non-null
+     * @param lowerBound lower bound of [bounds] to use if [start] is `null`
+     * @param upperBound upper bound of [bounds] to use if [end] is `null`
+     * @return whether this range is contained within [bounds]
+     */
+    fun isIn(
+        bounds: Range,
+        lowerBound: Int = bounds.start!!,
+        upperBound: Int = bounds.end!!,
+    ): Boolean {
+        val start = start ?: lowerBound
+        val end = end ?: upperBound
+        return start >= bounds.start!! && end <= bounds.end!!
+    }
+
+    /**
+     * Checks if this range (bounds) contains another range.
+     * Both [start] and [end] of the bounds range must be non-null.
+     * @param range range to check if this range contains
+     * @return whether this range contains [range].
+     */
+    operator fun contains(range: Range) = range.isIn(this)
+
     override fun toString() = "${start ?: ""}..${end ?: ""}"
 
     companion object {

stdlib/src/main/kotlin/eu/iamgio/quarkdown/stdlib/Data.kt

@@ -72,9 +72,17 @@ fun read(
     }
 
     // Lines from the file in the given range.
-    val lines = file.readLines().subList(lineRange)
+    val lines = file.readLines()
 
-    return lines.joinToString(System.lineSeparator()).wrappedAsValue()
+    // Check if the range is in bounds.
+    val bounds = Range(1, lines.size)
+    if (lineRange !in bounds) {
+        throw FunctionRuntimeException("Invalid range $lineRange in bounds $bounds")
+    }
+
+    return lines.subList(lineRange)
+        .joinToString(System.lineSeparator())
+        .wrappedAsValue()
 }
 
 /**

stdlib/src/test/kotlin/eu/iamgio/quarkdown/stdlib/DataTest.kt

@@ -11,6 +11,7 @@ import java.io.File
 import kotlin.test.BeforeTest
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFails
 import kotlin.test.assertIs
 
 private const val DATA_FOLDER = "src/test/resources/data"
@@ -53,6 +54,12 @@ class DataTest {
             "Line 4${LINE_SEPARATOR}Line 5",
             read(context, path, Range(4, null)).unwrappedValue,
         )
+
+        // Out of bounds ranges.
+        assertFails { read(context, path, Range(1, 8)) }
+        assertFails { read(context, path, Range(0, 3)) }
+        assertFails { read(context, path, Range(null, 9)) }
+        assertFails { read(context, path, Range(9, null)) }
     }
 
     @Test