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

Author: Enselic

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

@@ -93,6 +93,7 @@ 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

@@ -126,6 +126,7 @@ 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

@@ -713,6 +713,7 @@ 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

@@ -1312,7 +1312,7 @@ 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},