i've still been trying to get 21 to build in my free time. Realized that there were some issues with the update script that didn't fully populate device-dirs.json and vendor-dirs.json, specifically get_store_path in robotnix_common.py was returning the path with None/ appended to it. I addressed that, and it seems that the json files are fully populated. I did have to comment out adding a dependency to the vendor file (vendor/google/gs-common) as no repo seems to exist. Not sure where to find that repo. I tried building and now get a nix failure rather than an android build failure:

error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'cheetah-factory-2024060308.zip'
         whose name attribute is located at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/pkgs/stdenv/generic/make-derivation.nix:205:7

       … while evaluating attribute 'buildCommand' of derivation 'cheetah-factory-2024060308.zip'

         at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/pkgs/build-support/trivial-builders.nix:74:14:

           73|       name = lib.strings.sanitizeDerivationName name;
           74|       inherit buildCommand;
             |              ^
           75|       passAsFile = [ "buildCommand" ]

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: attribute '"vendor/google/gs-common"' missing

       at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/lib/attrsets.nix:107:50:

          106|   */
          107|   getAttrs = names: attrs: genAttrs names (name: attrs.${name});
             |                                                  ^
          108|

Ah yes, sorry:

       error: attribute '"vendor/google/gs-common"' missing

       at /nix/store/d0dl9ch4hhxkqikc1dw3868j95gsbb0h-source/lib/attrsets.nix:107:50:

          106|   */
          107|   getAttrs = names: attrs: genAttrs names (name: attrs.${name});
             |                                                  ^
          108|

Ok, it actually built around 300 source files! Then it failed with this:

note: keeping build directory '/tmp/nix-build-robotnix-lineage_cheetah-2024060317.drv-0'
error: builder for '/nix/store/ysklg1pa18cqjnlhf21i7qfrcmi6i8af-robotnix-lineage_cheetah-2024060317.drv' failed with exit code 1;
       last 10 log lines:
       > FAILED:
       > build/make/core/Makefile:5280: warning: Neither INSTALLED_KERNEL_TARGET nor INSTALLED_BOOTIMAGE_TARGET is defined when PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS  is true. Information about the updated kernel cannot be built into OTA update package. You can fix this by: (1) setting TARGET_NO_KERNEL to false and installing the built kernel to out/target/product/generic/kernel, so that kernel information will be extracted from the built kernel; or (2) Add a prebuilt boot image and specify it in BOARD_PREBUILT_BOOTIMAGE; or (3) extracting kernel configuration and defining BOARD_KERNEL_CONFIG_FILE and BOARD_KERNEL_VERSION manually; or (4) unsetting PRODUCT_OTA_ENFORCE_VINTF_KERNEL_REQUIREMENTS manually.
       > build/make/core/tasks/dex_preopt_check.mk:13: warning:  Missing compilation artifacts. Dexpreopting is not working for some system server jars. See https://cs.android.com/android/platform/superproject/+/master:build/make/core/tasks/README.dex_preopt_check.md
       > Offending entries:
       > system/framework/oat/arm/org.lineageos.platform.odex
       > system/framework/oat/arm/org.lineageos.platform.vdex
       > In file included from build/make/core/main.mk:1494:
       > In file included from build/make/core/Makefile:7695:
       > build/make/core/tasks/dex_preopt_check.mk:13: error: Build failed.
       > 18:46:51 ckati failed with: exit status 1
       For full logs, run 'nix log /nix/store/ysklg1pa18cqjnlhf21i7qfrcmi6i8af-robotnix-lineage_cheetah-2024060317.drv'.
error: 1 dependencies of derivation '/nix/store/bkhnbik6832pi7nbdzn6k1jn1h5q76ib-cheetah-factory-2024060317.zip.drv' failed to build