Also, move a few free-standing functions into StoreAPI and Derivation.

Also, introduce a non-nullable smart pointer, ref<T>, which is just a
wrapper around std::shared_ptr ensuring that the pointer is never
null. (For reference-counted values, this is better than passing a
"T&", because the latter doesn't maintain the refcount. Usually, the
caller will have a shared_ptr keeping the value alive, but that's not
always the case, e.g., when passing a reference to a std::thread via
std::bind.)

"tests/lang.sh" can handle this.

For example,

  $ nix-build --hash -A nix-repl.src

will build the fixed-output derivation nix-repl.src (a fetchFromGitHub
call), but instead of *verifying* the hash given in the Nix
expression, it prints out the resulting hash, and then moves the
result to its content-addressed location in the Nix store. E.g

  build produced path ‘/nix/store/504a4k6zi69dq0yjc0bm12pa65bccxam-nix-repl-8a2f5f06-src’ with sha256 hash ‘0cjablz01i0g9smnavhf86imwx1f9mnh5flax75i615ml71gsr88’

The goal of this is to make all nix-prefetch-* scripts unnecessary: we
can just let Nix run the real thing (i.e., the corresponding fetch*
derivation).

Another example:

  $ nix-build --hash -E 'with import <nixpkgs> {}; fetchgit { url = "https://github.com/NixOS/nix.git"; sha256 = "ffffffffffffffffffffffffffffffffffffffffffffffffffff"; }'
  ...
  git revision is 9e7c1a4b
  ...
  build produced path ‘/nix/store/gmsnh9i7x4mb7pyd2ns7n3c9l90jfsi1-nix’ with sha256 hash ‘1188xb621diw89n25rifqg9lxnzpz7nj5bfh4i1y3dnis0dmc0zp’

(Having to specify a fake sha256 hash is a bit annoying...)

nix-shell shebangs were broken by 9018deab

Revert "Revert "next try for "don't abort when given unmatched '}' with 'start-condition stack underflow'. This fixes  #751"""

This reverts commit b669d3d2.

Revert "next try for "don't abort when given unmatched '}' with 'start-condition stack underflow'. This fixes  #751""

This reverts commit ed23c856. Let's
merge this *after* the 1.11.1 release.

next try for "don't abort when given unmatched '}' with 'start-condition stack underflow'. This fixes  #751"

This reverts commit 8120b6fb and fixes the regression introduced in
8d22b264.

Revert "don't abort when given unmatched '}' with 'start-condition stack underflow'. This fixes  #751"

This reverts commit 8d22b264. It
breaks Nixpkgs:

$ nix-env -qa
error: syntax error, unexpected IND_STR, expecting '}', at /home/eelco/Dev/nixpkgs-stable/pkgs/top-level/python-packages.nix:7605:8

This should get rid of a certificate warning from "nix-env -i" early
in the install script.

Mention the --max-freed option in the nix-collect-garbage man page.
Related to https://github.com/NixOS/nix/issues/609.

Similar to 00903fa7. Regardless of -K,
we now also print which output differs.

Previously files in the Nix store were owned by root or by nixbld,
depending on whether they were created by a substituter or by a
builder. This doesn't matter much, but causes spurious diffoscope
differences. So use root everywhere.

This makes it easier to investigate the non-determinism, e.g.

  $ nix-build pkgs/stdenv/linux -A stage1.pkgs.zlib --check -K
  error: derivation ‘/nix/store/l54i8wlw22656i4pk05c52ngv9rpl39q-zlib-1.2.8.drv’ may not be deterministic: output ‘/nix/store/11a27shh6n2ivi4a7s964i65ql80cf27-zlib-1.2.8’ differs from ‘/nix/store/11a27shh6n2ivi4a7s964i65ql80cf27-zlib-1.2.8-check’

  $ diffoscope /nix/store/11a27shh6n2ivi4a7s964i65ql80cf27-zlib-1.2.8 /nix/store/11a27shh6n2ivi4a7s964i65ql80cf27-zlib-1.2.8-check
  ...
  ├── lib/libz.a
  │   ├── metadata
  │   │ @@ -1,15 +1,15 @@
  │   │ -rw-r--r-- 30001/30000   3096 Jan 12 15:20 2016 adler32.o
  ...
  │   │ +rw-r--r-- 30001/30000   3096 Jan 12 15:28 2016 adler32.o
  ...

This occured when sandbox building is disabled, at least one output
exists, and at least one other output does not.

E.g.

  $ nix-build pkgs/stdenv/linux/ -A stage1.pkgs.perl --check
  nix-store: src/libstore/build.cc:1323: void nix::DerivationGoal::tryToBuild(): Assertion `buildMode != bmCheck || validPaths.size() == drv->outputs.size()' failed.

when perl.out exists but perl.man doesn't. The fix is to only check
the outputs that exist. Note that "nix-build -A stage1.pkgs.all
--check" will still give a (proper) error in this case.

This reverts commit 80ebd60e. The
reason why we cleared CFLAGS/CXXFLAGS was because otherwise we get a
default value of -O2, which interferes with the defaults set in the
Makefile. (E.g. "make OPTIMIZE=0" should not pass -O2.)

This was observed in the deb_debian7x86_64 build:
http://hydra.nixos.org/build/29973215

Calling c_str() on a temporary should be fine because the temporary
shouldn't be destroyed until after the execl() call, but who knows...