Xcode error : Distill failed for unknown reasons

For me, I used with Xcode beta but I didn't upgrade my MAC OSX beta to the latest version as Apple recommends.

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For me the solution was to do the following (given I had no .psd as .png, etc.).

Go to the General tab of the Target in Xcode project settings, roll down to the "App Icons and Launch Images" section, and change the value of "App Icons Source" from "AppIcon" to "Don't use asset catalogs"

Note: this way the project builds and deploys on iOS, and later you can change the AppIcon settings back, adding your custom AppIcon (with proper file-format and file-extension).

In my case it was a PSD file saved as PNG. You can search for wrong files by running following command in Terminal in your assets directory:

grep -rL "PNG" --include \*.png . 

Xcode 11: I just removed Assets.xcassets and re-added to target, and it worked.

In my case I just forgot to initialize Git LFS for my repo.

I had the same error and it is because I forgot initializing Git LFS. So the png files are not pulled

Update or ensure minimum version is: Mac OS CATALINA BETA 10.15 beta (19A536g) and Xcode Version 11.0 beta 5 (11M382q)

After talking with an apple engineer, the problem was solved by updating MAC OS and Xcode, specifically to these versions I assure that the problem was solve.

If you hit this error, as a workaround, try removing all the images in you Images.xcassets from their placeholders and build the project again. Assuming the project builds without any images in place, which was the case for me, start re-adding images back one by one, starting from the bottom (App Store, iPad etc.) building project after each addition. This will help you isolate placeholders that cause the error.

In my case: the set of icons that comes with cocos2d-x project, the problem doesn't seem to be with a particular image, but with placeholder it is placed in. In particular, it seems to give an error on all placeholders whose name includes "iPhone". I can successfully build the project with all non-iPhone placeholders filled, but as soon as I move an image from say iPad placeholder to a compatible iPhone placeholder (e.g. iPad Notifications 20pt@2x to iPhone Notification 20pt@2x) the project fails with the above mentioned error.

I'm on the latest (as of right now) MacOS Catalina 10.15 Beta (19A487l) and the latest Xcode 11.3.1 (11C504), but I still hit this error, so the suggestions about to update to the latest won't necessarily work. The command line in both cases is:

/Applications/Xcode.app/Contents/Developer/usr/bin/actool --output-format human-readable-text --notices --warnings --export-dependency-info /Users/me/Library/Developer/Xcode/DerivedData/MyProject-eiofgcnvwliyntcmqdepcocwffyk/Build/Intermediates.noindex/MyProject.build/Debug-iphoneos/MyProject-mobile.build/assetcatalog_dependencies --output-partial-info-plist /Users/me/Library/Developer/Xcode/DerivedData/MyProject-eiofgcnvwliyntcmqdepcocwffyk/Build/Intermediates.noindex/MyProject.build/Debug-iphoneos/MyProject-mobile.build/assetcatalog_generated_info.plist --app-icon AppIcon --enable-on-demand-resources YES --filter-for-device-model iPhone10,6 --filter-for-device-os-version 13.3.1 --sticker-pack-identifier-prefix com.example.app.ios.sticker-pack. --development-region English --target-device iphone --target-device ipad --minimum-deployment-target 12.1 --platform iphoneos --product-type com.apple.product-type.application --compile /Users/me/Library/Developer/Xcode/DerivedData/MyProject-eiofgcnvwliyntcmqdepcocwffyk/Build/Products/Debug-iphoneos/MyProject-mobile.app /Users/me/Projects/Cocos/MyProject/proj.ios_mac/ios/Images.xcassets

In my case, there is a invalid png image in Assets.xcassets.

My image names that contained "ç" or that end with "é" caused the problem. Renaiming it and cleaning the project did the trick! Odly this naming worked on xcode 10 but no more on 11.1

I faced this error on Xcode_11.1 and completely wasted my whole week. then I realize it was Xcode itself bug, I tried many of the above answers but no luck.

to make sure it's Xcode bug just simply empty the asset folder the try to build with empty folder if errors still exist then downgrade or upgrade to another version my working version was Xcode_10.2.1

Hope it helps

After investing like 6-7 hours on this,I checked same project on MacOS Mojave - 10.14.6(18G103)and it was working fine but it was not working on MacOS Catalina Beta Version. After investigating, i updated the MacOS to the latest Catalina Beta Version and it was working fine.