There were some Warning messages that didn't make it into the log above for some reason.
.dub/packages/vibe-d/source/vibe/vpm/installation.d(35): Warning: const field with initializer should be static, __gshared, or an enum
Compiling diet template 'index.dt' (compat)...
.dub/packages/vibe-d/source/vibe/core/file.d(60): Warning: explicit element-wise assignment templ[16LU..__dollar - 1LU] = (suffix)[] is better than templ[16LU..__dollar - 1LU] = suffix