Fix yaml validation locations

src/model/validation/location.ts

@@ -46,6 +46,13 @@ export class MessageLocation {
                 value: new ProjectSource(this.sourceName, ''),
             });
         }
+
+        if (typeof _start !== 'number' && !(_start instanceof SourcePosition)) {
+            throw new Error(`start must be either a number or a SourcePosition`);
+        }
+        if (typeof _end !== 'number' && !(_end instanceof SourcePosition)) {
+            throw new Error(`end must be either a number or a SourcePosition`);
+        }
     }
 
     static from(location: LocationLike | undefined): MessageLocation | undefined {

src/schema/schema-builder.ts

@@ -201,21 +201,28 @@ function parseYAMLSource(
 
     root.errors.forEach((error) => {
         const severity = error.isWarning ? Severity.WARNING : Severity.ERROR;
-        const endPos = getLineEndPosition(error.mark.line + 1, projectSource);
+
+        // Errors reported do not have an end, only a start. We just choose the line end as the end.
+        // While there is a toLineEnd boolean, we ignore this, because what else would we really do?
+        let location: MessageLocation;
+        if (error.mark.position < projectSource.body.length) {
+            location = new MessageLocation(
+                projectSource,
+                new SourcePosition(error.mark.position, error.mark.line + 1, error.mark.column + 1),
+                getLineEndPosition(error.mark.line + 1, projectSource),
+            );
+        } else {
+            // This is an exception: An error can be reported at the EOL. Calculating the EOL would not work
+            // -> just report the error at the last character
+            location = new MessageLocation(
+                projectSource,
+                projectSource.body.length - 1,
+                projectSource.body.length,
+            );
+        }
+
         validationContext.addMessage(
-            new ValidationMessage({
-                severity,
-                message: error.reason,
-                location: new MessageLocation(
-                    projectSource,
-                    new SourcePosition(
-                        error.mark.position,
-                        error.mark.line + 1,
-                        error.mark.column + 1,
-                    ),
-                    endPos,
-                ),
-            }),
+            new ValidationMessage({ severity, message: error.reason, location }),
         );
     });
 

src/schema/schema-utils.ts

@@ -256,5 +256,5 @@ export function getLineEndPosition(targetLine: number, source: ProjectSource): S
         }
     }
 
-    return { line: targetLine, offset: curIndex - 1, column: column };
+    return new SourcePosition(curIndex - 1, targetLine, column);
 }