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14 commits

Author SHA1 Message Date
John Ericson 5eaea6cee0 cross stdenv: let build package's build deps resolve to native packages
This fixes the "sliding window" principle:
  0. Run packages:       build = native;  host = foreign; target = foreign;
  1. Build packages:     build = native;  host = native;  target = foreign;
  2. Vanilla packages:   build = native;  host = native;  target = native;
  3. Vanilla packages:   build = native;  host = native;  target = native;
  n+3. ...

Each stage's build dependencies are resolved against the previous stage,
and the "foreigns" are shifted accordingly. Vanilla packages alone are
built against themsevles, since there are no more "foreign"s to shift away.

Before, build packages' build dependencies were resolved against
themselves:
  0. Run packages:       build = native;  host = foreign; target = foreign;
  1. Build packages:     build = native;  host = native;  target = foreign;
  2. Build packages:     build = native;  host = native;  target = foreign;
  n+2. ...

This is wrong because that principle is violated by the target
platform staying foreign.

This will change the hashes of many build packages and run packages, but
that is OK. This is an unavoidable cost of fixing cross compiling.

The cross compilation docs have been updated to reflect this fix.
2017-02-05 12:01:53 -05:00
John Ericson 92edcb7ebb top-level: Lay the groundwork for {build,host,target}Platform
The long term goal is a big replace:
  { inherit system platform; } => buildPlatform
  crossSystem => hostPlatform
  stdenv.cross => targetPlatform
And additionally making sure each is defined even when not cross compiling.

This commit refactors the bootstrapping code along that vision, but leaves
the old identifiers with their null semantics in place so packages can be
modernized incrementally.
2017-01-24 11:37:56 -05:00
John Ericson bf17d6dacf top-level: Introduce buildPackages for resolving build-time deps
[N.B., this package also applies to the commits that follow it in the same
PR.]

In most cases, buildPackages = pkgs so things work just as before. For
cross compiling, however, buildPackages is resolved as the previous
bootstrapping stage. This allows us to avoid the mkDerivation hacks cross
compiling currently uses today.

To avoid a massive refactor, callPackage will splice together both package
sets. Again to avoid churn, it uses the old `nativeDrv` vs `crossDrv` to do
so. So now, whether cross compiling or not, packages with get a `nativeDrv`
and `crossDrv`---in the non-cross-compiling case they are simply the same
derivation. This is good because it reduces the divergence between the
cross and non-cross dataflow. See `pkgs/top-level/splice.nix` for a comment
along the lines of the preceding paragraph, and the code that does this
splicing.

Also, `forceNativeDrv` is replaced with `forceNativePackages`. The latter
resolves `pkgs` unless the host platform is different from the build
platform, in which case it resolves to `buildPackages`. Note that the
target platform is not important here---it will not prevent
`forcedNativePackages` from resolving to `pkgs`.

--------

Temporarily, we make preserve some dubious decisions in the name of preserving
hashes:

Most importantly, we don't distinguish between "host" and "target" in the
autoconf sense. This leads to the proliferation of *Cross derivations
currently used. What we ought to is resolve native deps of the cross "build
packages" (build = host != target) package set against the "vanilla
packages" (build = host = target) package set. Instead, "build packages"
uses itself, with (informally) target != build in all cases.

This is wrong because it violates the "sliding window" principle of
bootstrapping stages that shifting the platform triple of one stage to the
left coincides with the next stage's platform triple. Only because we don't
explicitly distinguish between "host" and "target" does it appear that the
"sliding window" principle is preserved--indeed it is over the reductionary
"platform double" of just "build" and "host/target".

Additionally, we build libc, libgcc, etc in the same stage as the compilers
themselves, which is wrong because they are used at runtime, not build
time. Fixing this is somewhat subtle, and the solution and problem will be
better explained in the commit that does fix it.

Commits after this will solve both these issues, at the expense of breaking
cross hashes. Native hashes won't be broken, thankfully.

--------

Did the temporary ugliness pan out? Of the packages that currently build in
`release-cross.nix`, the only ones that have their hash changed are
`*.gcc.crossDrv` and `bootstrapTools.*.coreutilsMinimal`. In both cases I
think it doesn't matter.

 1. GCC when doing a `build = host = target = foreign` build (maximally
    cross), still defines environment variables like `CPATH`[1] with
    packages.  This seems assuredly wrong because whether gcc dynamically
    links those, or the programs built by gcc dynamically link those---I
    have no idea which case is reality---they should be foreign. Therefore,
    in all likelihood, I just made the gcc less broken.

 2. Coreutils (ab)used the old cross-compiling infrastructure to depend on
    a native version of itself. When coreutils was overwritten to be built
    with fewer features, the native version it used would also be
    overwritten because the binding was tight. Now it uses the much looser
    `BuildPackages.coreutils` which is just fine as a richer build dep
    doesn't cause any problems and avoids a rebuild.

So, in conclusion I'd say the conservatism payed off. Onward to actually
raking the muck in the next PR!

[1]: https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html
2017-01-24 11:37:56 -05:00
Nicolas B. Pierron f5dfe78a1e Add overlays mechanism to Nixpkgs.
This patch add a new argument to Nixpkgs default expression named "overlays".

By default, the value of the argument is either taken from the environment variable `NIXPKGS_OVERLAYS`,
or from the directory `~/.nixpkgs/overlays/`.  If the environment variable does not name a valid directory
then this mechanism would fallback on the home directory.  If the home directory does not exists it will
fallback on an empty list of overlays.

The overlays directory should contain the list of extra Nixpkgs stages which would be used to extend the
content of Nixpkgs, with additional set of packages.  The overlays, i-e directory, files, symbolic links
are used in alphabetical order.

The simplest overlay which extends Nixpkgs with nothing looks like:

```nix
self: super: {
}
```

More refined overlays can use `super` as the basis for building new packages, and `self` as a way to query
the final result of the fix-point.

An example of overlay which extends Nixpkgs with a small set of packages can be found at:
  https://github.com/nbp/nixpkgs-mozilla/blob/nixpkgs-overlay/moz-overlay.nix

To use this file, checkout the repository and add a symbolic link to
the `moz-overlay.nix` file in `~/.nixpkgs/overlays` directory.
2017-01-16 01:17:33 +01:00
David Grayson 0f33b9f7f1 top-level: Do stdenvOverrides in stage.nix even if crossSystem exists.
Instead, the cross stdenv will patch up the override field -- the complexity
is now confined to the one place it matters.
2017-01-13 13:23:25 -05:00
John Ericson 3e197f7d81 top-level: Normalize stdenv booting
Introduce new abstraction, `stdenv/booter.nix` for composing bootstraping
stages, and use it everywhere for consistency. See that file for more doc.

Stdenvs besides Linux and Darwin are completely refactored to utilize this.
Those two, due to their size and complexity, are minimally edited for
easier reviewing.

No hashes should be changed.
2017-01-13 13:23:23 -05:00
John Ericson 39753f5360 top-level: Close over fewer arguments for stdenv stages
This makes the flow of data easier to understand. There's little downside
because the args in question are already inspected by the stdenvs.

cross-compiling in particular is simpler because we don't need to worry
about overriding the config closed over by `allPackages`.
2016-11-30 19:11:03 -05:00
John Ericson d240a0da1a top-level: Remove cycles: stdenv calls in top-level but not vice versa
This commit changes the dependencies of stdenv, and clean-up the stdenv
story by removing the `defaultStdenv` attribute as well as the `bootStdenv`
parameter.

Before, the final bootstrapping stage's stdenv was provided by
all-packages, which was iterating multiple times over the
top-level/default.nix expression, and non-final bootstrapping stages'
stdenvs were explicitly specified with the `bootStdenv` parameter.

Now, all stages' stdenvs are specified with the `stdenv` parameter.
For non-final bootstrapping stages, this is a small change---basically just
rename the parameter.
For the final stage, top-level/default.nix takes the chosen stdenv and
makes the final stage with it.

`allPackages` is used to make all bootstrapping stages, final and
non-final alike. It's basically the expression of `stage.nix` (along with a
few partially-applied default arguments)

Note, the make-bootstrap-tools scripts are temporarily broken
2016-11-30 19:10:59 -05:00
John Ericson 2df990967b Move up inherit binding for consistency 2016-11-30 19:03:22 -05:00
John Ericson ddeb0d2d6b top-level: Stop exposing all stdenvs 2016-11-30 19:03:01 -05:00
Shea Levy 7df3d7446f Add initial basic support for cross-compiling to iOS 2016-11-15 16:31:55 -05:00
John Ericson f68e16f023 top-level: Make cross compiling slightly saner
Removes the weird stdenv cycle used to match the old infrastructure.
It turns out that matching it so precisely is not needed.
2016-11-12 20:20:44 +01:00
John Ericson 6bfe04277f top-level: Make config-overriden stdenv bootstrap more normally 2016-11-06 21:28:38 -08:00
John Ericson e22346c35e top-level: Make stdenvCross which appears at first glance normal...
...but actually is weird just like the original
2016-11-06 21:27:38 -08:00