meson: hand the config.h conditions to Rust code

C code uses #if HAVE_FOO and Rust code uses #[cfg(HAVE_FOO)]. Turn
every HAVE_* and ENABLE_* key of config.h into a cfg that is set when
the key is 1. All of them are declared with --check-cfg so a misspelled
condition is reported instead of silently compiling the code out.

Programs get them through the rust_executables template and the
systemd_shared crate from the same list.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

meson.build

@@ -2278,6 +2278,7 @@ if have_rust
                 # Nothing from the crates is exported. The linker exports what a DSO in the link also defines,
                 # and a stub of the crates would then preempt it for the libraries a program loads.
                 'link_args' : ['-Wl,--exclude-libs,ALL'],
+                'rust_args' : rust_cfg_args,
         }
 
         rust_test_template = rust_executable_template + {

src/rust/systemd-shared/meson.build

@@ -6,6 +6,23 @@ endif
 
 rust = import('rust')
 
+# The config.h conditions, so that Rust code says #[cfg(HAVE_FOO)] where C code says #if HAVE_FOO, and a
+# misspelled one is reported.
+rust_cfg_args = []
+foreach key : conf.keys()
+        if key.startswith('HAVE_') or key.startswith('ENABLE_')
+                rust_cfg_args += '--check-cfg=cfg(@0@)'.format(key)
+                if '@0@'.format(conf.get(key)) == '1'
+                        rust_cfg_args += '--cfg=' + key
+                endif
+        endif
+endforeach
+# And the one C code gets from the compiler.
+rust_cfg_args += '--check-cfg=cfg(HAS_FEATURE_ADDRESS_SANITIZER)'
+if get_option('b_sanitize').contains('address')
+        rust_cfg_args += '--cfg=HAS_FEATURE_ADDRESS_SANITIZER'
+endif
+
 # Everything Rust code needs to use libsystemd-shared.
 shared_dep = declare_dependency(
         link_with : libshared,
@@ -159,4 +176,5 @@ libsystemd_shared_rs = static_library(
         'systemd_shared',
         systemd_shared_sources,
         rust_abi : 'rust',
+        rust_args : rust_cfg_args,
         link_with : [libsystemd_shared_sys])