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Expected to fail outside of Mac. But failing on Mac with:

FAILED: shaders/shader_fixtures.metallib 
python3 ../../flutter/impeller/tools/build_metal_library.py --output shaders/shader_fixtures.metallib --depfile /opt/s/w/ir/cache/builder/src/out/host_debug_unopt/gen/flutter/impeller/fixtures/shader_deps/shader_fixtures.depfile --platform=mac --source gen/flutter/impeller/fixtures/box_fade.vert.metal --source gen/flutter/impeller/fixtures/box_fade.frag.metal --source gen/flutter/impeller/fixtures/test_texture.vert.metal --source gen/flutter/impeller/fixtures/test_texture.frag.metal
metal: error: unknown argument: '-frecord-sources'

Maybe this is an xcode version issue? @jmagman can you remind me which version of XCode is on Engine CI. I also remember there were discussions about upgrading. Do you know which version the upgrade is targeting?

https://developer.apple.com/documentation/metal/libraries/generating_and_loading_a_metal_library_symbol_file seems to be saying that -frecord-sources is Xcode 13 and later.

https://developer.apple.com/documentation/metal/libraries/generating_and_loading_a_metal_library_symbol_file seems to be saying that -frecord-sources is Xcode 13 and later.

Ugh that's unfortunate, the engine builders are on Xcode 12.3. @yusuf-goog is working on getting the engine builders macOS version updated to unblock the migration to Xcode 13 https://docs.google.com/document/d/1M9HqJeEAisqgClRfxdXYBhYWJdiu2A-zSOovCBO7yjg/edit# (internal link)

We don't need Xcode 13 for Impeller. The -frecord-sources is the much more readable version of the older -M0 flag that puts sources and driver options in the compiled shader output so that profile mode builds enable shader debugging and profiling.

I used the newer flag after reading about it in the man page when I was re-reading my own code and could not figure out what M0 meant. I'll back it out.

Adjusted license checker for stb and filed flutter/flutter#97843 for its removal.