Quoting Debian Policy: Packages should build reproducibly, which for the purposes of this document [19] means that given
a version of a source package unpacked at a given path; a set of versions of installed build dependencies; a set of environment variable values; a build architecture; and a host architecture, repeatedly building the source package for the build architecture on any machine of the host architecture with those versions of the build dependencies installed and exactly those environment variable values set will produce bit-for-bit identical binary packages. So, according to this definition, if we can find a set of environment variable values and installed build-dependencies and a machine for which the package does not build at all (as I happen to find from time to time), then repeatedly building the source package in such machine will certainly not produce bit-for-bit identical binary packages, because it will not produce any binary packages at all, and therefore the package will not be reproducible by definition. Of course, this could be a bug in the wording, but if we really meant that the packages only need to be identical when they are actually produced, the wording should be like this instead: repeatedly building the source package will either produce a build failure or bit-for-bit identical binary packages. I guess this is not the type of reproducibility we should aim for. Thanks.