refact: Resolve some clippy warnings

(cherry picked from commit dc4bfaa993eb2d712d53f70551db9ac34b0cda08)

rust/nix-c-raw/build.rs

@@ -1,4 +1,3 @@
-use bindgen;
 use std::env;
 use std::path::PathBuf;
 

rust/nix-expr/src/eval_state.rs

@@ -52,8 +52,8 @@ impl EvalStateWeak {
     pub fn upgrade(&self) -> Option<EvalState> {
         self.inner.upgrade().and_then(|eval_state| {
             self.store.upgrade().map(|store| EvalState {
-                eval_state: eval_state,
-                store: store,
+                eval_state,
+                store,
                 context: Context::new(),
             })
         })

rust/nix-expr/src/primop.rs

@@ -55,10 +55,7 @@ impl PrimOp {
             // TODO: Use the GC with finalizer, if possible.
             let user_data = ManuallyDrop::new(Box::new(PrimOpContext {
                 arity: N,
-                function: Box::new(move |eval_state, args| {
-                    let r = f(eval_state, args.try_into().unwrap());
-                    r
-                }),
+                function: Box::new(move |eval_state, args| f(eval_state, args.try_into().unwrap())),
                 eval_state: eval_state.weak_ref(),
             }));
             user_data.as_ref() as *const PrimOpContext as *mut c_void

rust/nix-util/src/context.rs

@@ -18,10 +18,9 @@ impl Context {
             // We're almost certainly going to crash anyways.
             panic!("nix_c_context_create returned a null pointer");
         }
-        let ctx = Context {
+        Context {
             inner: NonNull::new(ctx).unwrap(),
-        };
-        ctx
+        }
     }
 
     /// Access the C context pointer.
@@ -36,7 +35,7 @@ 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::err_NIX_OK.try_into().unwrap() {
+        if err != raw::err_NIX_OK {
             // 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
@@ -50,7 +49,7 @@ impl Context {
         unsafe {
             raw::set_err_msg(
                 self.inner.as_ptr(),
-                raw::err_NIX_OK.try_into().unwrap(),
+                raw::err_NIX_OK,
                 b"\0".as_ptr() as *const i8,
             );
         }

rust/nix-util/src/string_return.rs

@@ -5,6 +5,12 @@ use anyhow::Result;
 /// This function is used by the other nix_* crates, and you should never need to call it yourself.
 ///
 /// Some functions in the nix library "return" strings without giving you ownership over them, by letting you pass a callback function that gets to look at that string. This callback simply turns that string pointer into an owned rust String.
+///
+/// # Safety
+///
+/// _Manual memory management_
+///
+/// Only for passing to the nix C API. Do not call this function directly.
 pub unsafe extern "C" fn callback_get_result_string(
     start: *const ::std::os::raw::c_char,
     n: std::os::raw::c_uint,
@@ -12,7 +18,7 @@ pub unsafe extern "C" fn callback_get_result_string(
 ) {
     let ret = user_data as *mut Result<String>;
 
-    if start == std::ptr::null() {
+    if start.is_null() {
         if n != 0 {
             panic!("callback_get_result_string: start is null but n is not zero");
         }
@@ -22,7 +28,7 @@ pub unsafe extern "C" fn callback_get_result_string(
 
     let slice = std::slice::from_raw_parts(start as *const u8, n as usize);
 
-    if !(*ret).is_err() {
+    if (*ret).is_ok() {
         panic!(
             "callback_get_result_string: Result must be initialized to Err. Did Nix call us twice?"
         );