transpile: replace pref_align_of with align_of in edition 2024 (#1656)

Since `core::intrinsics::pref_align_of` was removed, we can't fully
support `__alignof`/`__alignof__` anymore, but using normal
`core::mem::align_of` should still be a valid value.

This also updates `tests/unit/misc` to edition 2024, as its usage of
`__alignof__` was the only thing holding it back.

Author: kkysen

c2rust-transpile/src/translator/mod.rs

@@ -3379,17 +3379,36 @@ impl<'c> Translation<'c> {
         &self,
         mut type_id: CTypeId,
         preferred: bool,
+        src_loc: &Option<SrcSpan>,
     ) -> TranslationResult<WithStmts<Box<Expr>>> {
         type_id = self.variable_array_base_type(type_id);
 
         let ty = self.convert_type(type_id)?;
         let tys = vec![ty];
         let mut path = vec![mk().path_segment("core")];
-        if preferred {
+        // `core::intrinsics::pref_align_of` was removed in Rust 1.89
+        // (https://github.com/rust-lang/rust/pull/141803).
+        // There is no longer a notion of preferred alignment in Rust,
+        // so in edition 2024, we no longer support
+        // the non-standard `__alignof`/`__alignof__` extensions.
+        // Normal alignment should always be a valid preferred alignment,
+        // even if in a few cases, it is smaller,
+        // so rather than having a hard error here,
+        // we polyfill it with normal alignment.
+        if preferred && self.tcfg.edition < Edition2024 {
             self.use_feature("core_intrinsics");
             path.push(mk().path_segment("intrinsics"));
             path.push(mk().path_segment_with_args("pref_align_of", mk().angle_bracketed_args(tys)));
         } else {
+            if preferred {
+                let msg = "using `core::mem::align_of` instead of `core::intrinsics::pref_align_of` \
+                    for preferred alignment (`__alignof`/`__alignof__`) as the latter has been removed in Rust";
+                if let Some(loc) = self.ast_context.display_loc(src_loc) {
+                    warn!("{loc}: {msg}");
+                } else {
+                    warn!("{msg}");
+                }
+            }
             path.push(mk().path_segment("mem"));
             path.push(mk().path_segment_with_args("align_of", mk().angle_bracketed_args(tys)));
         }
@@ -3521,8 +3540,12 @@ impl<'c> Translation<'c> {
                             }
                         }
                     },
-                    UnTypeOp::AlignOf => self.compute_align_of_type(arg_ty.ctype, false)?,
-                    UnTypeOp::PreferredAlignOf => self.compute_align_of_type(arg_ty.ctype, true)?,
+                    UnTypeOp::AlignOf => {
+                        self.compute_align_of_type(arg_ty.ctype, false, src_loc)?
+                    }
+                    UnTypeOp::PreferredAlignOf => {
+                        self.compute_align_of_type(arg_ty.ctype, true, src_loc)?
+                    }
                 };
 
                 Ok(result)

tests/unit/misc/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "misc-tests"
 version = "0.1.0"
-edition = "2021"
+edition = "2024"
 
 [dependencies]

tests/unit/misc/src/test_call_only_once.rs

@@ -2,7 +2,7 @@ use crate::call_only_once::rust_assert_call_only_once;
 use std::ffi::c_int;
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn assert_call_only_once() -> c_int;
 }
 

tests/unit/misc/src/test_exprs.rs

@@ -4,7 +4,7 @@ use crate::exprs::rust_exprs;
 use std::ffi::{c_int, c_uint};
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn exprs(_: c_uint, _: *mut c_int);
 }
 

tests/unit/misc/src/test_lvalues.rs

@@ -2,7 +2,7 @@ use crate::lvalues::rust_lvalue;
 use std::ffi::c_int;
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn lvalue(_: *mut c_int);
 }
 

tests/unit/misc/src/test_memory.rs

@@ -3,7 +3,7 @@ use crate::strings_h::rust_setmem;
 use std::ffi::{c_int, c_uint};
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn malloc_test(_: c_uint, _: *mut c_int);
 
     fn setmem(_: c_uint, _: *mut c_int);

tests/unit/misc/src/test_quicksort.rs

@@ -4,7 +4,7 @@ use crate::qsort::{rust_partition, rust_quickSort, rust_swap};
 use std::ffi::c_int;
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn swap(_: *mut c_int, _: *mut c_int);
 
     fn partition(_: *mut c_int, _: c_int, _: c_int);

tests/unit/misc/src/test_shadowing.rs

@@ -2,7 +2,7 @@ use crate::shadowing::{rust_shadow, rust_twice};
 use std::ffi::{c_int, c_uint};
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn twice(_: c_int) -> c_int;
 
     fn shadow(_: c_uint, _: *mut c_int);

tests/unit/misc/src/test_sizeofs.rs

@@ -4,7 +4,7 @@ use crate::sizeofs::rust_sizeofs;
 use std::ffi::{c_int, c_uint};
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn sizeofs(_: c_uint, _: *mut c_int);
 }
 

tests/unit/misc/src/test_typedef.rs

@@ -5,7 +5,7 @@ use crate::typedef::{int_ptr, my_int, rust_entry};
 use std::ffi::c_int;
 
 #[link(name = "test")]
-extern "C" {
+unsafe extern "C" {
     fn entry() -> c_int;
 }