From b494d3e73dd17318032fa406f3deb73cc7b659ac Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Fri, 15 Aug 2025 09:13:23 +1000
Subject: [PATCH 1/2] Avoid unnecessary `mut`-ness for various closures.

---
 src/base.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/base.rs b/src/base.rs
index bc0a0f034b23..aefb9c9a1156 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -46,7 +46,7 @@ pub(crate) fn codegen_fn<'tcx>(
         with_no_trimmed_paths!({
             use rustc_middle::mir::pretty;
             let options = pretty::PrettyPrintMirOptions::from_cli(tcx);
-            pretty::write_mir_fn(tcx, mir, &mut |_, _| Ok(()), &mut buf, options).unwrap();
+            pretty::write_mir_fn(tcx, mir, &|_, _| Ok(()), &mut buf, options).unwrap();
         });
         String::from_utf8_lossy(&buf).into_owned()
     });

From 3293a0b6b7973f816652c4a2380eb897b4f262ed Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Fri, 15 Aug 2025 14:38:17 +1000
Subject: [PATCH 2/2] Introduce `MirDumper` and `MirWriter`.

MIR dumping is a mess. There are lots of functions and entry points,
e.g. `dump_mir`, `dump_mir_with_options`, `dump_polonius_mir`,
`dump_mir_to_writer`. Also, it's crucial that `create_dump_file` is
never called without `dump_enabled` first being checked, but there is no
mechanism for ensuring this and it's hard to tell if it is satisfied on
all paths. (`dump_enabled` is checked twice on some paths, however!)

This commit introduces `MirWriter`, which controls the MIR writing, and
encapsulates the `extra_data` closure and `options`. Two existing
functions are now methods of this type. It sets reasonable defaults,
allowing the removal of many `|_, _| Ok(())` closures.

The commit also introduces `MirDumper`, which is layered on top of
`MirWriter`, and which manages the creation of the dump files,
encapsulating pass names, disambiguators, etc. Four existing functions
are now methods of this type.
- `MirDumper::new` will only succeed if dumps are enabled, and will
  return `None` otherwise, which makes it impossible to dump when you
  shouldn't.
- It also sets reasonable defaults for various things like
  disambiguators, which means you no longer need to specify them in many
  cases. When they do need to be specified, it's now done via setter
  methods.
- It avoids some repetition. E.g. `dump_nll_mir` previously specifed the
  pass name `"nll"` four times and the disambiguator `&0` three times;
  now it specifies them just once, to put them in the `MirDumper`.
- For Polonius, the `extra_data` closure can now be specified earlier,
  which avoids having to pass some arguments through some functions.
---
 src/base.rs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/base.rs b/src/base.rs
index aefb9c9a1156..3a28dd7e73cb 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -44,9 +44,8 @@ pub(crate) fn codegen_fn<'tcx>(
     let _mir_guard = crate::PrintOnPanic(|| {
         let mut buf = Vec::new();
         with_no_trimmed_paths!({
-            use rustc_middle::mir::pretty;
-            let options = pretty::PrettyPrintMirOptions::from_cli(tcx);
-            pretty::write_mir_fn(tcx, mir, &|_, _| Ok(()), &mut buf, options).unwrap();
+            let writer = pretty::MirWriter::new(tcx);
+            writer.write_mir_fn(mir, &mut buf).unwrap();
         });
         String::from_utf8_lossy(&buf).into_owned()
     });