Few helpers. Now getLineRange throws on out of bounds line.

src/index.ts

@@ -240,19 +240,28 @@ export class SourceText {
     return this.sliceByCp(startCp, endCp);
   }
 
-  getLineRange(line: number): { start: CodePointIndex, end: CodePointIndex } {
+
+  tryGetLineRange(line: number): CodePointSpan | undefined {
     const lineIndex = line - 1;
+
     if (lineIndex < 0 || lineIndex >= this.lineStarts.length) {
-      // TODO: This is a bit suspicious. Maybe return undefined?
-      return { start: 0, end: 0 };
+      return undefined;
     }
 
     const start = this.lineStarts[lineIndex];
     const end = (lineIndex + 1 < this.lineStarts.length)
       ? this.lineStarts[lineIndex + 1]
       : this.#chars.length;
-      
-    return { start, end };
+
+    return rawSpan(start, end);
+  }
+
+  getLineRange(line: number): { start: CodePointIndex, end: CodePointIndex } {
+    const range = this.tryGetLineRange(line);
+    if (range === undefined) {
+      throw new Error(`Line ${line} is out of bounds (line count: ${this.lineCount})`);
+    }
+    return range;
   }
 }
 
@@ -308,6 +317,10 @@ export class SourceRegion {
     return span(loc, loc);
   }
 
+  get codePointSpan(): CodePointSpan {
+    return rawSpan(this.span.start.index, this.span.end.index);
+  }
+
   *codePoints(): IterableIterator<[CodePointIndex, CodePoint]> {
     const start = this.span.start.index;
     const end = this.span.end.index;
@@ -378,6 +391,16 @@ export type SourceLocation = {
   column: number; // 1-based
 }
 
+export function containsSpan(outer: CodePointSpan, inner: CodePointSpan): boolean {
+  return outer.start <= inner.start && inner.end <= outer.end;
+}
+
+export function containsIndex(span: CodePointSpan, index: CodePointIndex): boolean {
+  return span.start <= index && index < span.end;
+}
+
+// === Cursor ===
+
 export class SourceCursor {
   private index: CodePointIndex;
 
@@ -431,6 +454,11 @@ export class SourceCursor {
     return this.region.slice(span);
   }
 
+
+  location(): SourceLocation {
+    return this.region.source.getLocation(this.index);
+  }
+
   moveToNextLineStart(): void {
     const loc = this.region.source.getLocation(this.index);
     const nextLine = loc.line + 1;