From ee1d591e1a6ffcc792a1431edb458d1440dbf24d Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 29 Aug 2024 15:52:16 +0200
Subject: [PATCH] fix: Update for more recent Nix API

(cherry picked from commit 55355f03ab86dfa15972681d9a51d333739f6d10)
---
 rust/nix-expr/src/value.rs         |  4 ++--
 rust/nix-util/src/context.rs       | 10 +++++-----
 rust/nix-util/src/string_return.rs |  9 +++++++++
 3 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/rust/nix-expr/src/value.rs b/rust/nix-expr/src/value.rs
index 4fb9b62..77ef048 100644
--- a/rust/nix-expr/src/value.rs
+++ b/rust/nix-expr/src/value.rs
@@ -67,7 +67,7 @@ impl Drop for Value {
     fn drop(&mut self) {
         unsafe {
             // ignoring error because the only failure mode is leaking memory
-            raw::gc_decref(null_mut(), self.inner.as_ptr());
+            raw::value_decref(null_mut(), self.inner.as_ptr());
         }
     }
 }
@@ -77,7 +77,7 @@ impl Clone for Value {
         //       this is very unlikely to error, and it is not recoverable
         //       Maybe try without, and try again with context to report details?
         unsafe {
-            check_call!(raw::gc_incref(&mut Context::new(), self.inner.as_ptr())).unwrap();
+            check_call!(raw::value_incref(&mut Context::new(), self.inner.as_ptr())).unwrap();
         }
         // can't return an error here, but we don't want to ignore the error either as it means we could use-after-free
         Value { inner: self.inner }
diff --git a/rust/nix-util/src/context.rs b/rust/nix-util/src/context.rs
index f5db84d..55f0ab4 100644
--- a/rust/nix-util/src/context.rs
+++ b/rust/nix-util/src/context.rs
@@ -33,7 +33,7 @@ impl Context {
     /// We recommend to use `check_call!` if possible.
     pub fn check_err(&self) -> Result<()> {
         let err = unsafe { raw::err_code(self.inner.as_ptr()) };
-        if err != raw::NIX_OK.try_into().unwrap() {
+        if err != raw::err_NIX_OK.try_into().unwrap() {
             // msgp is a borrowed pointer (pointing into the context), so we don't need to free it
             let msgp = unsafe { raw::err_msg(null_mut(), self.inner.as_ptr(), null_mut()) };
             // Turn the i8 pointer into a Rust string by copying
@@ -47,7 +47,7 @@ impl Context {
         unsafe {
             raw::set_err_msg(
                 self.inner.as_ptr(),
-                raw::NIX_OK.try_into().unwrap(),
+                raw::err_NIX_OK.try_into().unwrap(),
                 b"\0".as_ptr() as *const i8,
             );
         }
@@ -66,7 +66,7 @@ impl Context {
         f: F,
     ) -> Result<Option<T>> {
         let t = f(self.ptr());
-        if unsafe { raw::err_code(self.inner.as_ptr()) == raw::NIX_ERR_KEY } {
+        if unsafe { raw::err_code(self.inner.as_ptr()) == raw::err_NIX_ERR_KEY } {
             self.clear();
             return Ok(None);
         }
@@ -109,7 +109,7 @@ macro_rules! check_call_opt_key {
         {
             let ctx : &mut $crate::context::Context = $ctx;
             let ret = $($f)::*(ctx.ptr(), $($arg,)*);
-            if unsafe { raw::err_code(ctx.ptr()) == raw::NIX_ERR_KEY } {
+            if unsafe { raw::err_code(ctx.ptr()) == raw::err_NIX_ERR_KEY } {
                 ctx.clear();
                 return Ok(None);
             }
@@ -140,7 +140,7 @@ mod tests {
         unsafe {
             raw::set_err_msg(
                 ctx_ptr,
-                raw::NIX_ERR_UNKNOWN.try_into().unwrap(),
+                raw::err_NIX_ERR_UNKNOWN.try_into().unwrap(),
                 b"dummy error message\0".as_ptr() as *const i8,
             );
         }
diff --git a/rust/nix-util/src/string_return.rs b/rust/nix-util/src/string_return.rs
index 004f1ae..f06fa32 100644
--- a/rust/nix-util/src/string_return.rs
+++ b/rust/nix-util/src/string_return.rs
@@ -11,6 +11,15 @@ pub unsafe extern "C" fn callback_get_result_string(
     user_data: *mut std::os::raw::c_void,
 ) {
     let ret = user_data as *mut Result<String>;
+
+    if start == std::ptr::null() {
+        if n != 0 {
+            panic!("callback_get_result_string: start is null but n is not zero");
+        }
+        *ret = Ok(String::new());
+        return;
+    }
+
     let slice = std::slice::from_raw_parts(start as *const u8, n as usize);
 
     if !(*ret).is_err() {