Blueprint files are described as "pseudo-python data format", and the Python comment character is #. However, apparently Blueprint actually uses C-style // and /* ... */ comments. This should be documented somewhere.

I've been experimenting with Blueprints in a setup where there are some 3rd party components with a build system that already produces ninja output. My initial assumption was that writing a Blueprint rule to invoke that 3rd party tool, and then include/subninja the resulting file, would be a practical way to do this. There doesn't seem to be a way to do this right now. I had started on a patch to do so. Before I finish plumbing it through, I wanted to see if I was missing a better way, or perhaps if you would consider it out of the design space of Blueprints.

Documentation points to http://martine.github.io/ninja
Should it be replaced by https://github.com/ninja-build/ninja ?

I'm building aosp Android 9. and from time to time I got this error that stop my build without any specific scenario. after some hours it can run without problems, even without any change in the code base.

out/soong/.bootstrap/blueprint-microfactory/test/test.passed -- out/soong/.bootstrap/blueprint-microfactory/test/test -test.short
--- FAIL: TestRebuildAfterRemoveOut (0.40s)
microfactory_test.go:191: Output timestamp should be different, but both were 2020-01-19 16:43:14 +0200 IST
--- FAIL: TestRebuildAfterPartialBuild (0.43s)
microfactory_test.go:191: Output timestamp should be different, but both were 2020-01-19 16:43:14 +0200 IST
--- FAIL: TestRebuildAfterMainChange (0.45s)
microfactory_test.go:191: Output timestamp should be different, but both were 2020-01-19 16:43:14 +0200 IST
--- FAIL: TestRebuildAfterGoChange (0.58s)
microfactory_test.go:191: Output timestamp should be different, but both were 2020-01-19 16:43:14 +0200 IST
FAIL
[ 0% 170/93074] //external/aac:libFraunhoferAAC clang++ libFDK/src/FDK_tools_rom.cpp
ninja: build stopped: subcommand failed.
16:43:15 ninja failed with: exit status 1

I have looked everywhere and have not found any documentation on this build system. Is there even documentation to begin with.