--- a/libpam-sys/src/constants.rs	Sat Jun 28 00:34:45 2025 -0400
+++ b/libpam-sys/src/constants.rs	Sat Jun 28 02:49:35 2025 -0400
@@ -1,8 +1,6 @@
 //! All the constants.
 
-// We have to enable these otherwise we get lit up with warnings
-// during conditional compilation.
-#![allow(dead_code, unused_imports)]
+use libpam_sys_impls::cfg_pam_impl;
 
 /// Macro to make defining a bunch of constants way easier.
 macro_rules! define {
@@ -16,63 +14,40 @@
     (@expand $({ $(#[$m:meta])* } $i:item)+) => {$($(#[$m])* $i)+};
 }
 
-#[cfg(feature = "use-system-headers")]
-pub use system_headers::*;
-
-#[cfg(not(feature = "use-system-headers"))]
-pub use export::*;
-
-mod export {
-    // There are a few truly universal constants.
-    // They are defined here directly.
-    pub const PAM_SUCCESS: u32 = 0;
+// There are a few truly universal constants.
+// They are defined here directly.
+pub const PAM_SUCCESS: u32 = 0;
 
-    define!(
-        /// An item type.
-        PAM_SERVICE = 1;
-        PAM_USER = 2;
-        PAM_TTY = 3;
-        PAM_RHOST = 4;
-        PAM_CONV = 5;
-        PAM_AUTHTOK = 6;
-        PAM_OLDAUTHTOK = 7;
-        PAM_RUSER = 8;
-    );
+define!(
+    /// An item type.
+    PAM_SERVICE = 1;
+    PAM_USER = 2;
+    PAM_TTY = 3;
+    PAM_RHOST = 4;
+    PAM_CONV = 5;
+    PAM_AUTHTOK = 6;
+    PAM_OLDAUTHTOK = 7;
+    PAM_RUSER = 8;
+);
 
-    define!(
-        /// A message style.
-        PAM_PROMPT_ECHO_OFF = 1;
-        PAM_PROMPT_ECHO_ON = 2;
-        PAM_ERROR_MSG = 3;
-        PAM_TEXT_INFO = 4;
-    );
-
-    define!(
-        /// Maximum size of PAM conversation elements (suggested).
-        PAM_MAX_NUM_MSG = 32;
-        PAM_MAX_MSG_SIZE = 512;
-        PAM_MAX_RESP_SIZE = 512;
-    );
+define!(
+    /// A message style.
+    PAM_PROMPT_ECHO_OFF = 1;
+    PAM_PROMPT_ECHO_ON = 2;
+    PAM_ERROR_MSG = 3;
+    PAM_TEXT_INFO = 4;
+);
 
-    #[cfg(pam_impl = "linux-pam")]
-    pub use super::linux_pam::*;
-
-    #[cfg(not(pam_impl = "linux-pam"))]
-    pub use super::illumos_openpam::*;
-
-    #[cfg(pam_impl = "illumos")]
-    pub use super::illumos::*;
+define!(
+    /// Maximum size of PAM conversation elements (suggested).
+    PAM_MAX_NUM_MSG = 32;
+    PAM_MAX_MSG_SIZE = 512;
+    PAM_MAX_RESP_SIZE = 512;
+);
 
-    #[cfg(pam_impl = "openpam")]
-    pub use super::openpam::*;
-}
-
-/// Constants extracted from PAM header files.
-mod system_headers {
-    // include!(concat!(env!("OUT_DIR"), "/constants.rs"));
-}
-
-/// Constants used by Linux-PAM.
+#[cfg_pam_impl("LinuxPam")]
+pub use linux_pam::*;
+#[cfg_pam_impl("LinuxPam")]
 mod linux_pam {
     define!(
         /// An error code.
@@ -145,7 +120,9 @@
     );
 }
 
-/// Constants shared between Illumos and OpenPAM.
+#[cfg_pam_impl(any("Illumos", "OpenPam", "OpenPamMinimal"))]
+pub use illumos_openpam;
+#[cfg_pam_impl(any("Illumos", "OpenPam", "OpenPamMinimal"))]
 mod illumos_openpam {
     define!(
         /// An error code.
@@ -207,6 +184,9 @@
 }
 
 /// Constants exclusive to Illumos.
+#[cfg_pam_impl("Illumos")]
+pub use illumos::*;
+#[cfg_pam_impl("Illumos")]
 mod illumos {
     /// The total number of PAM error codes.
     pub const PAM_TOTAL_ERRNUM: u32 = 28;
@@ -221,7 +201,9 @@
     pub const PAM_NO_AUTHTOK_CHECK: u32 = 0b1000;
 }
 
-/// Constants exclusive to OpenPAM.
+#[cfg_pam_impl("OpenPam")]
+pub use openpam::*;
+#[cfg_pam_impl("OpenPam")]
 mod openpam {
     define!(
         /// An error code.