fix: Require mutable Context, as it should be

This spreads out transitively to many places and requires that
we use `check_call!` instead of `check_one_call` in a number of
places.

(cherry picked from commit 6bc31dcf206518a7be7f0ac6e773d5dfe25531ea)

rust/nix-util/src/context.rs

@@ -47,7 +47,7 @@ impl Context {
         Ok(())
     }
 
-    fn clear(&self) {
+    pub fn clear(&mut self) {
         unsafe {
             raw::set_err_msg(
                 self.inner.as_ptr(),
@@ -57,7 +57,7 @@ impl Context {
         }
     }
 
-    pub fn check_err_and_clear(&self) -> Result<()> {
+    pub fn check_err_and_clear(&mut self) -> Result<()> {
         let r = self.check_err();
         if r.is_err() {
             self.clear();
@@ -68,14 +68,14 @@ impl Context {
     /// Run the function, and check the error, then reset the error.
     /// Make at most one call to a Nix function in `f`.
     /// Do not use if the context isn't fresh or cleared (e.g. with `check_err_and_clear`).
-    pub fn check_one_call<T, F: FnOnce(*mut raw::c_context) -> T>(&self, f: F) -> Result<T> {
+    pub fn check_one_call<T, F: FnOnce(*mut raw::c_context) -> T>(&mut self, f: F) -> Result<T> {
         let t = f(self.ptr());
         self.check_err_and_clear()?;
         Ok(t)
     }
 
     pub fn check_one_call_or_key_none<T, F: FnOnce(*mut raw::c_context) -> T>(
-        &self,
+        &mut self,
         f: F,
     ) -> Result<Option<T>> {
         let t = f(self.ptr());

rust/nix-util/src/settings.rs

@@ -7,7 +7,7 @@ use crate::{
 };
 
 pub fn set(key: &str, value: &str) -> Result<()> {
-    let ctx = context::Context::new();
+    let mut ctx = context::Context::new();
     let key = std::ffi::CString::new(key)?;
     let value = std::ffi::CString::new(value)?;
     ctx.check_one_call(|ctx_ptr| unsafe {
@@ -16,7 +16,7 @@ pub fn set(key: &str, value: &str) -> Result<()> {
 }
 
 pub fn get(key: &str) -> Result<String> {
-    let ctx = context::Context::new();
+    let mut ctx = context::Context::new();
     let key = std::ffi::CString::new(key)?;
     let mut r: Result<String> = result_string_init!();
     ctx.check_one_call(|ctx_ptr| unsafe {
@@ -32,15 +32,16 @@ pub fn get(key: &str) -> Result<String> {
 
 #[cfg(test)]
 mod tests {
+    use crate::check_call;
+
     use super::*;
 
     #[ctor::ctor]
     fn setup() {
-        let ctx = context::Context::new();
-        ctx.check_one_call(|ctx_ptr| unsafe {
-            nix_c_raw::libstore_init(ctx_ptr);
-        })
-        .unwrap();
+        let mut ctx = context::Context::new();
+        unsafe {
+            check_call!(raw::libstore_init[ctx]).unwrap();
+        }
     }
 
     #[test]