meson: move nix3 manpage generation into command-ref/

This puts the generated files where they are for the make system.
This is in preparation for further meson-mdbook stuff.

Change-Id: I934df6854a80af5ccf381cf1da0bda0187a8bcfc

doc/manual/meson.build

@@ -132,19 +132,10 @@ nix3_cli_json = custom_target(
   capture : true,
   output : 'nix.json',
 )
-nix3_cli_files = custom_target(
-  command : nix_eval_for_docs + [
-    '--write-to', '@OUTPUT@',
-    '--expr',
-    'import @INPUT1@ true (builtins.readFile @INPUT0@)',
-  ],
-  input : [
-    nix3_cli_json,
-    'generate-manpage.nix',
-    'utils.nix',
-  ],
-  output : 'new-cli',
-)
+
+# Creates nix3_cli_files custom target variable,
+# which outputs the entire src/command-ref/new-cli directory.
+subdir('src/command-ref')
 
 nix3_manpages = [
   'nix3-build',
@@ -245,6 +236,7 @@ foreach page : nix3_manpages
       '@OUTPUT@.tmp',
       '@OUTPUT@',
     ],
+    # nix3_cli_files set in doc/manual/src/command-ref/meson.build.
     input : nix3_cli_files,
     output : page + '.1',
     install : true,

doc/manual/src/command-ref/meson.build

@@ -0,0 +1,16 @@
+nix3_cli_files = custom_target(
+  'command-ref-new-cli',
+  command : nix_eval_for_docs + [
+    '--write-to', '@OUTPUT@',
+    '--expr',
+    'import @INPUT1@ true (builtins.readFile @INPUT0@)',
+  ],
+  input : [
+    nix3_cli_json,
+    files(
+      meson.project_source_root() / 'doc/manual/generate-manpage.nix',
+      meson.project_source_root() / 'doc/manual/utils.nix',
+    ),
+  ],
+  output : 'new-cli',
+)