Hack together a fix for the public headers

Please fix this.

src/libexpr/expr-config.hh

@@ -0,0 +1,3 @@
+// TODO: Remove this damn file while keeping public config headers working
+#error \
+    "This file is a placeholder. It only exists so that meson accepts the symbolic link include/nix/expr/config.hh to this file, but we expect meson to overwrite it with the real file. Apparently that did not happen. I deeply apologize for this mess."

src/libexpr/include/nix/expr/config.hh

@@ -0,0 +1 @@
+../../../expr-config.hh

src/libexpr/include/nix/expr/meson.build

@@ -10,6 +10,7 @@ config_pub_h = configure_file(
 headers = [config_pub_h] + files(
   'attr-path.hh',
   'attr-set.hh',
+  'config.hh',
   'eval-cache.hh',
   'eval-error.hh',
   'eval-gc.hh',

src/libexpr/meson.build

@@ -79,6 +79,11 @@ config_priv_h = configure_file(
   output : 'expr-config-private.hh',
 )
 
+config_pub_h = configure_file(
+  configuration : configdata_pub,
+  output : 'expr-config.hh',
+)
+
 subdir('nix-meson-build-support/common')
 
 parser_tab = custom_target(
@@ -163,6 +168,8 @@ subdir('primops')
 subdir('nix-meson-build-support/export-all-symbols')
 subdir('nix-meson-build-support/windows-version')
 
+headers += [config_pub_h]
+
 this_library = library(
   'nixexpr',
   sources,
@@ -181,4 +188,8 @@ install_headers(headers, subdir : 'nix/expr', preserve_path : true)
 
 libraries_private = []
 
+nixexpr_dep = declare_dependency(
+  include_directories : include_directories('.'),
+  link_with : this_library,
+)
 subdir('nix-meson-build-support/export')

src/libmain/meson.build

@@ -17,6 +17,8 @@ subdir('nix-meson-build-support/deps-lists')
 configdata = configuration_data()
 
 deps_private_maybe_subproject = [
+  # This dependency may be very limited; was introduced for NIX_USE_BOEHMGC macro dependency
+  dependency('nix-expr'),
 ]
 deps_public_maybe_subproject = [
   dependency('nix-util'),

src/libmain/package.nix

@@ -6,6 +6,7 @@
 
   nix-util,
   nix-store,
+  nix-expr,
 
   # Configuration Options
 
@@ -33,6 +34,10 @@ mkMesonLibrary (finalAttrs: {
   ];
 
   propagatedBuildInputs = [
+    # FIXME: This is only here for the NIX_USE_BOEHMGC macro dependency
+    #        Removing nix-expr will make the build more concurrent and is
+    #        architecturally nice, perhaps.
+    nix-expr
     nix-util
     nix-store
     openssl

src/libstore-tests/meson.build

@@ -40,6 +40,9 @@ deps_private += gtest
 configdata = configuration_data()
 configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
 
+aws_s3 = dependency('aws-cpp-sdk-s3', required : false)
+configdata.set('ENABLE_S3', aws_s3.found().to_int())
+
 config_priv_h = configure_file(
   configuration : configdata,
   output : 'store-tests-config.hh',

src/libstore/meson.build

@@ -158,6 +158,7 @@ if get_option('embedded-sandbox-shell')
   # The path to busybox is passed as a -D flag when compiling this_library.
   # This solution is inherited from the old make buildsystem
   # TODO: do this differently?
+  # TODO: at least define it unconditionally, so we get checking from -Wundef
   configdata_priv.set('HAVE_EMBEDDED_SANDBOX_SHELL', 1)
   hexdump = find_program('hexdump', native : true)
   embedded_sandbox_shell_gen = custom_target(
@@ -181,6 +182,11 @@ config_priv_h = configure_file(
   output : 'store-config-private.hh',
 )
 
+config_pub_h = configure_file(
+  configuration : configdata_pub,
+  output : 'store-config.hh',
+)
+
 subdir('nix-meson-build-support/common')
 
 sources = files(
@@ -362,7 +368,7 @@ this_library = library(
   install : true,
 )
 
-install_headers(headers, subdir : 'nix/store', preserve_path : true)
+install_headers(headers + [ config_pub_h ], subdir : 'nix/store', preserve_path : true)
 
 libraries_private = []