Make functional tests on NixOS use Meson not Make

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

tests/functional/common/init.sh

@@ -19,7 +19,7 @@ EOF
 
   # When we're doing everything in the same store, we need to bring
   # dependencies into context.
-  sed -i "$(dirname "${BASH_SOURCE[0]}")"/../config.nix \
+  sed -i "${_NIX_TEST_BUILD_DIR}/config.nix" \
     -e 's^\(shell\) = "/nix/store/\([^/]*\)/\(.*\)";^\1 = builtins.appendContext "/nix/store/\2" { "/nix/store/\2".path = true; } + "/\3";^' \
     -e 's^\(path\) = "/nix/store/\([^/]*\)/\(.*\)";^\1 = builtins.appendContext "/nix/store/\2" { "/nix/store/\2".path = true; } + "/\3";^' \
     ;

tests/functional/common/subst-vars.sh.in

@@ -1,4 +1,4 @@
-# NOTE: instances of @variable@ are substituted as defined in /mk/templates.mk
+# NOTE: instances of @variable@ are substituted by the build system
 
 if [[ -z "${COMMON_SUBST_VARS_SH_SOURCED-}" ]]; then
 

tests/functional/meson.build

@@ -1,4 +1,4 @@
-project('nix-functional-tests', 'cpp',
+project('nix-functional-tests',
   version : files('.version'),
   default_options : [
     'cpp_std=c++2a',
@@ -170,6 +170,7 @@ suites = [
 
 nix_store = dependency('nix-store', required : false)
 if nix_store.found()
+  add_languages('cpp')
   subdir('test-libstoreconsumer')
   suites += {
     'name': 'libstoreconsumer',
@@ -187,6 +188,7 @@ endif
 # Plugin tests require shared libraries support.
 nix_expr = dependency('nix-expr', required : false)
 if nix_expr.found() and get_option('default_library') != 'static'
+  add_languages('cpp')
   subdir('plugins')
   suites += {
     'name': 'plugins',