Rollup merge of #86450 - tmiasko:move-size-limit, r=pnkfelix

Add flag to configure `large_assignments` lint

The `large_assignments` lints detects moves over specified limit.  The
limit is configured through `move_size_limit = "N"` attribute placed at
the root of a crate. When attribute is absent, the lint is disabled.

Make it possible to enable the lint without making any changes to the
source code, through a new flag `-Zmove-size-limit=N`.  For example, to
detect moves exceeding 1023 bytes in a cargo crate, including all
dependencies one could use:

```
$ env RUSTFLAGS=-Zmove-size-limit=1024 cargo build -vv
```

Lint tracking issue #83518.

3 files changed, 9 insertions, 1 deletions

diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index b1e4e3ba395..de0d5fb0097 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -735,6 +735,7 @@ fn test_debugging_options_tracking_hash() {
     tracked!(merge_functions, Some(MergeFunctions::Disabled));
     tracked!(mir_emit_retag, true);
     tracked!(mir_opt_level, Some(4));
+    tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, Some(true));
     tracked!(new_llvm_pass_manager, Some(true));
     tracked!(no_generate_arange_section, true);
diff --git a/compiler/rustc_middle/src/middle/limits.rs b/compiler/rustc_middle/src/middle/limits.rs
index c4bfd0ebb2f..7ea4902f4bc 100644
--- a/compiler/rustc_middle/src/middle/limits.rs
+++ b/compiler/rustc_middle/src/middle/limits.rs
@@ -21,7 +21,12 @@ use std::num::IntErrorKind;
 pub fn provide(providers: &mut ty::query::Providers) {
     providers.limits = |tcx, ()| Limits {
         recursion_limit: get_recursion_limit(tcx.hir().krate_attrs(), tcx.sess),
-        move_size_limit: get_limit(tcx.hir().krate_attrs(), tcx.sess, sym::move_size_limit, 0),
+        move_size_limit: get_limit(
+            tcx.hir().krate_attrs(),
+            tcx.sess,
+            sym::move_size_limit,
+            tcx.sess.opts.debugging_opts.move_size_limit.unwrap_or(0),
+        ),
         type_length_limit: get_limit(
             tcx.hir().krate_attrs(),
             tcx.sess,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 9fbe4c05ef9..0805d2f0e14 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1148,6 +1148,8 @@ options! {
         (default: no)"),
     mir_opt_level: Option<usize> = (None, parse_opt_number, [TRACKED],
         "MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
+    move_size_limit: Option<usize> = (None, parse_opt_number, [TRACKED],
+        "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes for LLVM >= 12, otherwise no)"),
     new_llvm_pass_manager: Option<bool> = (None, parse_opt_bool, [TRACKED],