* guix/scripts/substitute.scm (or*): New macro.
(%cache-url): Honor "untrusted-substitute-urls".
* guix/tests.scm (%test-substitute-urls): New variable.
(open-connection-for-tests): Use it.
* tests/derivations.scm ("derivation-prerequisites-to-build and substitutes",
"derivation-prerequisites-to-build and substitutes, non-substitutable
build", "derivation-prerequisites-to-build and substitutes, local build"):
Pass it to 'set-build-options'.
* tests/guix-daemon.sh: Likewise.
* tests/store.scm ("substitute query, alternating URLs"): New test.
("substitute query", "substitute", "substitute + build-things with output
path", "substitute, corrupt output hash", "substitute --fallback"): Pass
#:substitute-urls to 'set-build-options'.
* test-env.in: New file.
* configure.ac: Add it to `AC_CONFIG_FILES' and `commands-exec'.
* config-daemon.ac: Set and substitute `GUIX_TEST_ROOT'.
* Makefile.am (SCM_LOG_COMPILER, SH_LOG_COMPILER): Use it in lieu of
`pre-inst-env'.
* daemon.am (test_root): Remove
(AM_TESTS_ENVIRONMENT): Remove `TEST_ROOT'.
(clean-local): Use $(GUIX_TEST_ROOT); make files writable before
removing them.guix_test_root
* tests/guix-daemon.sh: Remove `NIX_' variable settings; don't launch
`guix-daemon'.
* nix/scripts/list-runtime-roots.in: New file.
* config-daemon.ac: Add `AC_CONFIG_FILES' invocation for it.
* daemon.am (nodist_pkglibexec_SCRIPTS): New variable.
(AM_TESTS_ENVIRONMENT): Define `top_builddir'.
* tests/guix-daemon.sh: Export `NIX_ROOT_FINDER'.
* nix/sync-with-upstream: Substitute the path to the root finder in
libstore/gc.cc.
