SceneKit doesn't build, says it needs an output file

The error you're encountering suggests that Xcode's build system expects a specific output file from the shell script build rule for processing the .scn file. SceneKit's .scn files are typically processed by Xcode during the build phase, and the build rule needs to specify an output to ensure the file is correctly managed.

Here’s how you can resolve this issue:

Check the Build Phase:

Go to your project in Xcode. Select your target. Navigate to the “Build Phases” tab. Look for the build phase that involves your .scn file. Edit the Shell Script Build Rule:

If there is a custom shell script build rule, ensure that it declares an output file. This informs Xcode about the expected result of running the script. Here is an example of a shell script build rule: sh

Shell script content to process SceneKit file

echo "Processing ${SCRIPT_INPUT_FILE_0}"

Example command (adjust as needed)

/usr/bin/scntool --convert ${SCRIPT_INPUT_FILE_0} --output ${SCRIPT_OUTPUT_FILE_0}

In the "Output Files" section, specify the expected outp ${SCRIPT_INPUT_FILE_0}.processed

Ensure Proper File Paths:

Verify that the paths provided in the script match the actual locations of your input and output files. Verify File Integration:

Ensure the .scn file is correctly added to the project and the target membership is checked. Here’s a step-by-step guide to properly set up the shell script build rule:

Step-by-Step Guide: Add the .scn file:

Make sure the .scn file is part of the project and is listed under the “Copy Bundle Resources” build phase if it needs to be included in the app bundle. Add a Shell Script Build Phase:

If you need to add a new build phase: Click on the "+" button at the top left of the “Build Phases” tab. Select "New Run Script Phase". Configure the Shell Script:

In the newly added run script phase, you can add the necessary shell script commands.

Example command to process SceneKit file

/usr/bin/scntool --convert "${SRCROOT}/path/to/Scene.scn" --output "${TARGET_BUILD_DIR}/${UNLOCALIZED_RESOURCES_FOLDER_PATH}/Scene.processed.scn"

Example command to process SceneKit file

/usr/bin/scntool --convert "${SRCROOT}/path/to/Scene.scn" --output "${TARGET_BUILD_DIR}/${UNLOCALIZED_RESOURCES_FOLDER_PATH}/Scene.processed.scn"

Specify Input and Output Files:

In the "Input Files" section, add the path to your .scn file:

${SRCROOT}/path/to/Scene.scn

In the "Output Files" section, add the path to the expected output

${TARGET_BUILD_DIR}/${UNLOCALIZED_RESOURCES_FOLDER_PATH}/Scene.processed.scn

Rebuild the Project:

Clean and rebuild the project to ensure the changes take effect. Summary: Ensure your shell script build rule specifies both input and output files to satisfy Xcode’s build system requirements. This helps Xcode track dependencies and build artifacts correctly. By following these steps, you should be able to resolve the error and correctly process your SceneKit .scn files.

Figured it out: in the Build Rules section of the .xcodeproj file there was a null script being created for some reason. Once I removed it, the error went away.