Auto merge of #115684 - Enselic:large_assignments-default, r=<try>

Set default `move_size_limit` to 4kB for `large_assignments` lint on nightly

Only enable it by default in the nightly compiler. The limit can be changed on a per-crate basis with:

    #![feature(large_assignments)]
    #![move_size_limit = "8192"]

or with

    -Zmove-size-limit=8192

Does the _"enable the lint by default with a 4k threshold"_ step in #83518.

TODO:
 - [ ] Figure out how to write a test that tests that the stable compiler still has a default move_size_limit of 0. I suspect it is easy once you know the trick, but I haven't been able to figure out the trick yet.
 - [ ] I found a bug where the lint is duplicated unnecessarily when generic instantiations are involved. See FIXME in the test. We should file an issue about it so we don't forget it. Or at least write a row in the tracking issue.
 - [ ] The compiler seems very slow after this change. Might be tricky to fix..

r? `@oli-obk` who is E-mentor.

Author: bors

compiler/rustc_interface/src/passes.rs

@@ -716,6 +716,7 @@ pub fn create_global_ctxt<'tcx>(
 
     sess.time("setup_global_ctxt", || {
         gcx_cell.get_or_init(move || {
+            #[allow(large_assignments)]
             TyCtxt::create_global_ctxt(
                 sess,
                 crate_types,

compiler/rustc_interface/src/queries.rs

@@ -91,6 +91,7 @@ pub struct Queries<'tcx> {
 
 impl<'tcx> Queries<'tcx> {
     pub fn new(compiler: &'tcx Compiler) -> Queries<'tcx> {
+        #[allow(large_assignments)]
         Queries {
             compiler,
             gcx_cell: OnceLock::new(),

compiler/rustc_interface/src/tests.rs

@@ -1,4 +1,4 @@
-#![allow(rustc::bad_opt_access)]
+#![allow(rustc::bad_opt_access, large_assignments)]
 use crate::interface::parse_cfgspecs;
 
 use rustc_data_structures::fx::FxHashSet;

compiler/rustc_interface/src/util.rs

@@ -128,6 +128,7 @@ pub fn create_session(
     sess.parse_sess.config = cfg;
     sess.parse_sess.check_config = check_cfg;
 
+    #[allow(large_assignments)]
     (sess, codegen_backend)
 }
 

compiler/rustc_middle/src/middle/limits.rs

@@ -25,7 +25,15 @@ pub fn provide(providers: &mut Providers) {
             tcx.hir().krate_attrs(),
             tcx.sess,
             sym::move_size_limit,
-            tcx.sess.opts.unstable_opts.move_size_limit.unwrap_or(0),
+            // The check is enabled by default in nightly compilers without
+            // needing `#![feature(large_assignments)]` with a limit of 4096
+            // bytes. But if the user wants to use adjust `#![move_size_limit]`,
+            // then `#![feature(large_assignments)]` is needed.
+            tcx.sess.opts.unstable_opts.move_size_limit.unwrap_or(if tcx.sess.is_nightly_build() {
+                4096
+            } else {
+                0
+            }),
         ),
         type_length_limit: get_limit(
             tcx.hir().krate_attrs(),

compiler/rustc_middle/src/ty/context.rs

@@ -711,6 +711,7 @@ impl<'tcx> TyCtxt<'tcx> {
         let common_lifetimes = CommonLifetimes::new(&interners);
         let common_consts = CommonConsts::new(&interners, &common_types);
 
+        #[allow(large_assignments)]
         GlobalCtxt {
             sess: s,
             crate_types,

compiler/rustc_query_impl/src/lib.rs

@@ -209,6 +209,7 @@ pub fn query_system<'tcx>(
     on_disk_cache: Option<OnDiskCache<'tcx>>,
     incremental: bool,
 ) -> QuerySystem<'tcx> {
+    #[allow(large_assignments)]
     QuerySystem {
         states: Default::default(),
         arenas: Default::default(),

compiler/rustc_session/src/session.rs

@@ -1318,7 +1318,7 @@ fn default_emitter(
 }
 
 // JUSTIFICATION: literally session construction
-#[allow(rustc::bad_opt_access)]
+#[allow(rustc::bad_opt_access, large_assignments)]
 pub fn build_session(
     handler: &EarlyErrorHandler,
     sopts: config::Options,

compiler/rustc_target/src/spec/apple/tests.rs

@@ -1,3 +1,5 @@
+#![allow(large_assignments)]
+
 use crate::spec::{
     aarch64_apple_darwin, aarch64_apple_ios_sim, aarch64_apple_watchos_sim, i686_apple_darwin,
     x86_64_apple_darwin, x86_64_apple_ios, x86_64_apple_tvos, x86_64_apple_watchos_sim,

library/alloc/benches/vec_deque.rs

@@ -1,3 +1,5 @@
+#![allow(large_assignments)]
+
 use core::iter::Iterator;
 use std::{
     collections::{vec_deque, VecDeque},

library/alloc/src/boxed.rs

@@ -837,6 +837,7 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
     ///
     /// ```
     /// #![feature(new_uninit)]
+    /// #![allow(large_assignments)]
     ///
     /// let big_box = Box::<[usize; 1024]>::new_uninit();
     ///

library/core/benches/array.rs

@@ -1,3 +1,5 @@
+#![allow(large_assignments)]
+
 use test::black_box;
 use test::Bencher;
 

library/core/benches/iter.rs

@@ -1,3 +1,5 @@
+#![allow(large_assignments)]
+
 use core::borrow::Borrow;
 use core::iter::*;
 use core::mem;

library/core/src/cell.rs

@@ -2042,6 +2042,7 @@ impl<T> UnsafeCell<T> {
     #[rustc_const_stable(feature = "const_unsafe_cell_new", since = "1.32.0")]
     #[inline(always)]
     pub const fn new(value: T) -> UnsafeCell<T> {
+        #[allow(large_assignments)]
         UnsafeCell { value }
     }
 

library/core/src/convert/mod.rs

@@ -713,6 +713,7 @@ where
     /// <code>[From]&lt;T&gt; for U</code> chooses to do.
     #[inline]
     fn into(self) -> U {
+        #[allow(large_assignments)]
         U::from(self)
     }
 }

library/core/src/hint.rs

@@ -290,6 +290,7 @@ pub fn spin_loop() {
 #[stable(feature = "bench_black_box", since = "1.66.0")]
 #[rustc_const_unstable(feature = "const_black_box", issue = "none")]
 pub const fn black_box<T>(dummy: T) -> T {
+    #[allow(large_assignments)]
     crate::intrinsics::black_box(dummy)
 }
 

library/core/src/mem/maybe_uninit.rs

@@ -97,6 +97,7 @@ use crate::slice;
 /// unnecessary moves.
 ///
 /// ```
+/// ##![allow(large_assignments)]
 /// use std::mem::MaybeUninit;
 ///
 /// unsafe fn make_vec(out: *mut Vec<i32>) {
@@ -117,6 +118,7 @@ use crate::slice;
 /// `MaybeUninit<T>` can be used to initialize a large array element-by-element:
 ///
 /// ```
+/// ##![allow(large_assignments)]
 /// use std::mem::{self, MaybeUninit};
 ///
 /// let data = {
@@ -145,6 +147,7 @@ use crate::slice;
 /// be found in low-level datastructures.
 ///
 /// ```
+/// ##![allow(large_assignments)]
 /// use std::mem::MaybeUninit;
 ///
 /// // Create an uninitialized array of `MaybeUninit`. The `assume_init` is

tests/ui/async-await/large_moves.attribute.stderr

@@ -28,12 +28,60 @@ LL |     let _ = NotBox::new([0; 9999]);
    = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
 error: moving 9999 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 1500 bytes
+  --> $DIR/large_moves.rs:37:13
+   |
+LL |     let _ = NotBox::new([0; 1500]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 2500 bytes
   --> $DIR/large_moves.rs:41:13
    |
+LL |     let _ = NotBox::new([0; 2500]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:47:13
+   |
+LL |     let _ = NotBox::new([0; 5000]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 1500 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 2500 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
 LL |             data,
    |             ^^^^ value moved from here
    |
    = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
-error: aborting due to 4 previous errors
+error: aborting due to 10 previous errors
 

tests/ui/async-await/large_moves.nothing.stderr

@@ -0,0 +1,55 @@
+error: moving 10024 bytes
+  --> $DIR/large_moves.rs:21:14
+   |
+LL |     let z = (x, 42);
+   |              ^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+note: the lint level is defined here
+  --> $DIR/large_moves.rs:1:9
+   |
+LL | #![deny(large_assignments)]
+   |         ^^^^^^^^^^^^^^^^^
+
+error: moving 10024 bytes
+  --> $DIR/large_moves.rs:22:13
+   |
+LL |     let a = z.0;
+   |             ^^^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 9999 bytes
+  --> $DIR/large_moves.rs:27:13
+   |
+LL |     let _ = NotBox::new([0; 9999]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 9999 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:47:13
+   |
+LL |     let _ = NotBox::new([0; 5000]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 4096, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: aborting due to 6 previous errors
+

tests/ui/async-await/large_moves.option.stderr

@@ -4,7 +4,7 @@ error: moving 10024 bytes
 LL |     let z = (x, 42);
    |              ^ value moved from here
    |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 note: the lint level is defined here
   --> $DIR/large_moves.rs:1:9
    |
@@ -17,23 +17,55 @@ error: moving 10024 bytes
 LL |     let a = z.0;
    |             ^^^ value moved from here
    |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
 error: moving 9999 bytes
   --> $DIR/large_moves.rs:27:13
    |
 LL |     let _ = NotBox::new([0; 9999]);
    |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
    |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
 error: moving 9999 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 2500 bytes
   --> $DIR/large_moves.rs:41:13
    |
+LL |     let _ = NotBox::new([0; 2500]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:47:13
+   |
+LL |     let _ = NotBox::new([0; 5000]);
+   |             ^^^^^^^^^^^^^^^^^^^^^^ value moved from here
+   |
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 2500 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
+LL |             data,
+   |             ^^^^ value moved from here
+   |
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+
+error: moving 5000 bytes
+  --> $DIR/large_moves.rs:63:13
+   |
 LL |             data,
    |             ^^^^ value moved from here
    |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
+   = note: The current maximum size is 2000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
-error: aborting due to 4 previous errors
+error: aborting due to 8 previous errors