Use a meson "generator" to deduplicate .gen.hh creation

build-utils-meson/generate-header/meson.build

@@ -0,0 +1,7 @@
+bash = find_program('bash', native: true)
+
+gen_header = generator(
+  bash,
+  arguments : [ '-c', '{ echo \'R"__NIX_STR(\' && cat @INPUT@ && echo \')__NIX_STR"\'; } > "$1"', '_ignored_argv0', '@OUTPUT@' ],
+  output : '@PLAINNAME@.gen.hh',
+)

meson.build

@@ -6,6 +6,7 @@ project('nix-dev-shell', 'cpp',
   subproject_dir : 'src',
 )
 
+# Internal Libraries
 subproject('libutil')
 subproject('libstore')
 subproject('libfetchers')
@@ -18,7 +19,7 @@ subproject('libcmd')
 subproject('internal-api-docs')
 subproject('external-api-docs')
 
-# C wrappers
+# External C wrapper libraries
 subproject('libutil-c')
 subproject('libstore-c')
 subproject('libexpr-c')

src/libexpr/meson.build

@@ -116,20 +116,17 @@ lexer_tab = custom_target(
   install_dir : get_option('includedir') / 'nix',
 )
 
+subdir('build-utils-meson/generate-header')
+
 generated_headers = []
 foreach header : [
   'imported-drv-to-derivation.nix',
   'fetchurl.nix',
   'call-flake.nix',
 ]
-  generated_headers += custom_target(
-    command : [ 'bash', '-c', '{ echo \'R"__NIX_STR(\' && cat @INPUT@ && echo \')__NIX_STR"\'; } > "$1"', '_ignored_argv0', '@OUTPUT@' ],
-    input : header,
-    output : '@PLAINNAME@.gen.hh',
-  )
+  generated_headers += gen_header.process(header)
 endforeach
 
-
 sources = files(
   'attr-path.cc',
   'attr-set.cc',

src/libexpr/primops/meson.build

@@ -1,12 +1,7 @@
-foreach header : [
+generated_headers += gen_header.process(
   'derivation.nix',
-]
-  generated_headers += custom_target(
-    command : [ 'bash', '-c', '{ echo \'R"__NIX_STR(\' && cat @INPUT@ && echo \')__NIX_STR"\'; } > "$1"', '_ignored_argv0', '@OUTPUT@' ],
-    input : header,
-    output : '@PLAINNAME@.gen.hh',
-  )
-endforeach
+  preserve_path_from: meson.project_source_root(),
+)
 
 sources += files(
   'context.cc',

src/libstore/meson.build

@@ -99,18 +99,14 @@ deps_public += nlohmann_json
 sqlite = dependency('sqlite3', 'sqlite', version : '>=3.6.19')
 deps_private += sqlite
 
+subdir('build-utils-meson/generate-header')
+
 generated_headers = []
 foreach header : [
   'schema.sql',
   'ca-specific-schema.sql',
 ]
-  generated_headers += custom_target(
-    command : [ 'bash', '-c', '{ echo \'R"__NIX_STR(\' && cat @INPUT@ && echo \')__NIX_STR"\'; } > "$1"', '_ignored_argv0', '@OUTPUT@' ],
-    input : header,
-    output : '@PLAINNAME@.gen.hh',
-    install : true,
-    install_dir : get_option('includedir') / 'nix',
-  )
+  generated_headers += gen_header.process(header)
 endforeach
 
 busybox = find_program(get_option('sandbox-shell'), required : false)