If 1.4 is going to become the bootstrap toolset, that also suggests that 1.4 will essentially become "long-term supported", meaning that if new ports require fixes to the bootstrap toolset (even in the cross-compilation) scenario, hopefully they'll accept those changes upstream.
For the foreseeable future, it must be possible to build the compiler with Go 1.4. That means the compiler must stick to Go 1.4 libraries and constructs (or use build tags for conditional compilation). It says nothing about which version of Go you have to use to build the compiler. If we're working on Go 1.9 and you want to use Go 1.7 as the bootstrap base, that's fine: Go 1.7 will build and run everything that Go 1.4 does. You just can't introduce any Go 1.7-specific code into the compiler.
I don't know if you've noticed, but there are very few language changes in each release. We're focused on improvements to performance and reliability more than new features. So I don't anticipate it being a hardship that the compiler is limited to Go 1.4. (And that's still much nicer than C.)
I don't feel like I have this backwards at all.
I wasn't commenting on it being a hardship to limit the implementation to Go 1.4's feature set.
For example, Go 1.4 did not support linux/ppc64, but Go 1.5 will. If you want to build Go 1.5 for linux/ppc64 from source, the simplest thing to do is to cross-compile it on a linux/amd64 system, copy the resulting binaries over to your linux/ppc64 system, and use that toolchain as the bootstrap base for any future work.
Doing two ports would work, but the first one is basically wasted effort unless you need to survive every other supported Go system disappearing tomorrow.
I was under the impression from reading the boostrap document that this meant I would have to port 1.4 and 1.5. I think I completely misunderstood the new ports section as to how it related to the plan overall.
If I can get away with only porting a newer version, that's considerably easier.
Thanks for assuaging my fears.
To build Go 1.x, for x ≥ 5, it will be necessary to have
Go 1.4 installed already, in $GOROOT_BOOTSTRAP.
For Go 1.x (x ≥ 5), new ports will have to be done by
cross-compiling test binaries on a working system,
copying the binaries over to the target, and running and
debugging them there.Go is already very good at cross-compiling. That can be used to do a new port (as a trivial example, the fact that the compiler doesn't run on NaCl didn't hurt the NaCl port at all). There is a section in the doc explicitly about this. We are doing new ports too (like power64), and I don't anticipate the bootstrapping change slowing them down appreciably.
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This is an odd thing to say. Go cross-compiles exactly as well as it compiles. If you write a go_YOUROS_YOURARCH_exec script that copies the binary over to your target system and runs it, you can sit at any working system (for concreteness, any x86 system running Linux, OS X, or Windows) and work in a full Go environment. That's actually better than sitting on an unsupported system editing C files and unable to run any program written in Go.
Shouldn't it be possible to port to a new system simply by porting Go 1.4 to that system? Once that base version is ported, a script can build 1.4, then build 1.5 and any succeeding base versions until the current version is reached.
Of course, system-specific features would have to be added for each go release beyond 1.4, but that would have to be done anyway.
What am I missing?
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Does go not support being cross compiled/cross compiling?