* nix/libstore/build.cc (DerivationGoal::tryBuildHook): Use starts_with instead
of string()
* nix/libstore/builtins.cc (lookupBuiltinBuilder): Same.
* nix/libstore/builtins.hh (isBuiltin): Same and fix indentation of the file.
* nix/libstore/derivations.cc (DerivationOutput::parseHashInfo, isDerivation):
Same and clean header files.
* nix/libstore/gc.cc (addPermRoot, LocalStore::isActiveTempFile): Same.
* nix/libstore/globals.cc: Same.
* nix/libstore/local-store.cc: Same.
* nix/libstore/misc.cc: Same.
* nix/libstore/store-api.cc (checkStoreName): Same.
* nix/libutil/affinity.cc: Same.
* nix/libutil/archive.cc: Same.
* nix/libutil/spawn.cc: Same.
* nix/libutil/util.{cc, hh} (hasSuffix): Removed.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

* nix/boost: This directory and all files inside it are removed.
* nix/libstore/build.cc (Goal::trace): Use ‘std::string’ instead of ‘const format &’.
(DerivationGoal::startBuilder, ...): Use ‘std::format’ or ‘std::vformat’ instead of ‘boost::format’.
* nix/libstore/builtins.cc (builtinDownload): Same.
* nix/libstore/derivations.cc (DerivationOutput::parseHashInfo, ...): Same.
* nix/libstore/gc.cc (LocalStore::openGCLock, ...): Same.
* nix/libstore/globals.cc (Settings::_get): Same.
* nix/libstore/local-store.cc: (checkStoreNotSymlink, ...): Same.
* nix/libstore/misc.cc (dfsVisit, showBytes): Same
* nix/libstore/optimise-store.cc (makeWritable, ...): Same.
* nix/libstore/pathlocks.cc (openLockFile, ...): Same.
* nix/libstore/references.cc (search, scanForReferences): Same.
* nix/libstore/sqlite.hh (throwSQLiteError): Use ‘std::string’ instead of ‘const format &’.
* nix/libstore/sqlite.cc (throwSQLiteError): Use ‘std::string’ instead of ‘const format &’.
* nix/libstore/store-api.cc (assertStorePath, ...): Use ‘std::format’ instead of ‘boost::format’.
* nix/libutil/affinity.cc (setAffinityTo): Same.
* nix/libutil/archive.cc (dumpContents, ...): Same.
* nix/libutil/hash.cc (parseHash, parseHash32, parseHash16or32, hashFile): Same.
* nix/libutil/hash.hh (parseHash, parseHash32, parseHash16or32, isHash): Same.
* nix/libutil/serialise.cc : Add ‘<cassert>’ header file.
* nix/libutil/spawn.cc (addPhaseAfter, ...): Use ‘std::format’ instead of ‘boost::format’.
* nix/libutil/types.hh (FormatOrString): Removed.
(BaseError, BaseError::addPrefix, SysError, MakeError):
Use ‘std::string or std::string_view’ instead of ‘FormatOrString’.
* nix/libutil/util.hh (Nest::open, printMsg_, warnOnce, expect): Same.
* nix/libutil/util.cc (BaseError::BaseError, ...): Same.
(writeToStderr, _interrupted): Use std::uncaught_exceptions() instead of std::uncaught_exception()
* nix/nix-daemon/nix-daemon.cc (performOp, ...): Same.
* nix/nix-daemon/guix-daemon.cc (string_to_bool, ...): Same.
* nix/local.mk: Remove ‘libformat.a’ from ‘noinst_LIBRARIES’,
remove ‘libformat_a_SOURCES’ and ‘libformat_headers’,
remove ‘libformat_a_CPPFLAGS’ from ‘libutil_a_CPPFLAGS’ and ‘guix_daemon_LDADD’,
update ‘AM_CXXFLAGS’ to ‘-std=c++20’.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

The new builder makes it possible to break cycles that occurs when the
fixed-output derivation for the source of a dependency of ‘git’ would
itself depend on ‘git’.

* guix/scripts/perform-download.scm (perform-git-download): New
procedure.
(perform-download): Move fixed-output derivation check to…
(guix-perform-download): … here.  Invoke ‘perform-download’ or
‘perform-git-download’ depending on what ‘derivation-builder’ returns.
* nix/libstore/builtins.cc (builtins): Add “git-download”.
* tests/derivations.scm ("built-in-builders"): Update.
("'git-download' built-in builder")
("'git-download' built-in builder, invalid hash")
("'git-download' built-in builder, invalid commit")
("'git-download' built-in builder, not found"): New tests.

* nix/scripts/download.in: Remove.
* nix/local.mk (nodist_pkglibexec_SCRIPTS): Remove 'scripts/download'.
* config-daemon.ac: Don't output 'nix/scripts/download'.
* nix/libstore/builtins.cc (builtinDownload): Invoke 'guix
perform-download' directly.

This makes it easier to run the uninstalled daemon.

* nix/local.mk (libstore_a_CPPFLAGS): Append "/guix" to
NIX_LIBEXEC_DIR.
* build-aux/pre-inst-env.in (NIX_LIBEXEC_DIR): Adjust comment.
* nix/libstore/builtins.cc (builtinDownload): Remove SUBDIR and its
use.
* nix/libstore/local-store.cc (runAuthenticationProgram): Ditto.
* nix/libstore/gc.cc (addAdditionalRoots): Remove "/guix" prefix.
* nix/nix-daemon/guix-daemon.cc (main): Ditto.

* guix/scripts/perform-download.scm (perform-download): Add
 #:print-build-trace? and pass it to 'url-fetch'.
(guix-perform-download): Define 'print-build-trace?' and pass it to
'perform-download'.
* guix/build/download.scm (ftp-fetch): Add #:print-build-trace? and
honor it.
(url-fetch): Likewise.
* nix/libstore/builtins.cc (builtinDownload): Set _NIX_OPTIONS
environment variable.

Reported by rohit yadav <rohityadav@utexas.edu>
at <https://lists.gnu.org/archive/html/guix-devel/2017-02/msg00191.html>.

This fixes a regression whereby 'guix perform-download' would always see
NIX_STORE as unset and thus use "/gnu/store", leading it to miscompute
the hydra.gnu.org content-addressed URLs when the store file name is not
"/gnu/store".

* nix/libstore/builtins.cc (builtinDownload): Add 'setenv' call for
'NIX_STORE'.

Fixes <http://bugs.gnu.org/25089>.
Reported by Leo Famulari <leo@famulari.name>.

* nix/libstore/build.cc (DerivationGoal::runChild): In the 'isBuiltin'
case, check whether DRV's output is in 'redirectedOutputs', and pass an
'output' argument to the built-in builder.
(DerivationGoal::addHashRewrite): Add 'printMsg' call.
* nix/libstore/builtins.hh (derivationBuilder): Add 'output' parameter.
* nix/libstore/builtins.cc (builtinDownload): Likewise.
Add OUTPUT to ARGV.
* guix/scripts/perform-download.scm (perform-download): Add 'output'
parameter.
(guix-perform-download): Adjust 'match' clauses accordingly.
* tests/derivations.scm ("'download' built-in builder, check mode"): New
test.

* nix/libstore/builtins.cc (builtinBuilderNames): New function.
* nix/libstore/builtins.hh (builtinBuilderNames): New declaration.
* nix/libstore/worker-protocol.hh (PROTOCOL_VERSION): Bump to 0x160.
(WorkerOp)[wopBuiltinBuilders]: New value.
* nix/nix-daemon/nix-daemon.cc (performOp): Handle it.
* guix/store.scm (operation-id)[built-in-builders]: New value.
* guix/store.scm (read-arg): Add 'string-list'.
(built-in-builders): New procedure.
* tests/derivations.scm ("built-in-builders"): New test.

This ensures that 1) the derivation doesn't change when Guix changes;
2) the derivation closure doesn't contain Guix and its dependencies; 3)
we don't have to rely on ugly chroot hacks.

Adapted from Nix commit 0a2bee307b20411f5b0dda0c662b1f9bb9e0e131.

* nix/libstore/build.cc (DerivationGoal::runChild): Add special case for
'isBuiltin(drv)'.  Disable chroot when 'isBuiltin(drv)'.
* nix/libstore/builtins.cc, nix/libstore/builtins.hh,
nix/scripts/download.in, guix/scripts/perform-download.scm: New files.
* guix/ui.scm (show-guix-help)[internal?]: Add 'perform-download'.
* nix/local.mk (libstore_a_SOURCES): Add builtins.cc.
(libstore_headers): Add builtins.hh.
(nodist_pkglibexec_SCRIPTS): Add 'scripts/download'.
* config-daemon.ac: Emit 'scripts/download'.
* Makefile.am (MODULES): Add 'guix/scripts/perform-download.scm'.
* tests/derivations.scm ("unknown built-in builder")
("'download' built-in builder")
("'download' built-in builder, invalid hash")
("'download' built-in builder, not found")
("'download' built-in builder, not fixed-output"): New tests.

Co-authored-by: Eelco Dolstra <eelco.dolstra@logicblox.com>