diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs
index 5e70b300f33..a54332b6f25 100644
--- a/compiler/rustc_mir_transform/src/instsimplify.rs
+++ b/compiler/rustc_mir_transform/src/instsimplify.rs
@@ -219,10 +219,8 @@ fn simplify_cast(&self, rvalue: &mut Rvalue<'tcx>) {
                     for (i, field) in variant.fields.iter_enumerated() {
                         let field_ty = field.ty(self.tcx, args);
                         if field_ty == *cast_ty {
-                            let place = place.project_deeper(
-                                &[ProjectionElem::Field(i, *cast_ty)],
-                                self.tcx,
-                            );
+                            let place = place
+                                .project_deeper(&[ProjectionElem::Field(i, *cast_ty)], self.tcx);
                             let operand = if operand.is_move() {
                                 Operand::Move(place)
                             } else {
diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 6df32169eec..8d7547d03e8 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -691,7 +691,7 @@ fn visit_projection_elem(
                                 location,
                                 format!(
                                     "You can't project to field {f:?} of `DynMetadata` because \
-                                         layout is weird and thinks it doesn't have fields."
+                                     layout is weird and thinks it doesn't have fields."
                                 ),
                             );
                         }
diff --git a/library/core/src/ptr/metadata.rs b/library/core/src/ptr/metadata.rs
index e501970b580..6dfeb66694d 100644
--- a/library/core/src/ptr/metadata.rs
+++ b/library/core/src/ptr/metadata.rs
@@ -209,18 +209,14 @@ pub fn size_of(self) -> usize {
         // Consider a reference like `&(i32, dyn Send)`: the vtable will only store the size of the
         // `Send` part!
         // SAFETY: DynMetadata always contains a valid vtable pointer
-        return unsafe {
-            crate::intrinsics::vtable_size(self.vtable_ptr() as *const ())
-        };
+        return unsafe { crate::intrinsics::vtable_size(self.vtable_ptr() as *const ()) };
     }
 
     /// Returns the alignment of the type associated with this vtable.
     #[inline]
     pub fn align_of(self) -> usize {
         // SAFETY: DynMetadata always contains a valid vtable pointer
-        return unsafe {
-            crate::intrinsics::vtable_align(self.vtable_ptr() as *const ())
-        };
+        return unsafe { crate::intrinsics::vtable_align(self.vtable_ptr() as *const ()) };
     }
 
     /// Returns the size and alignment together as a `Layout`
diff --git a/rustfmt.toml b/rustfmt.toml
index 4812c9302df..b78e96d5872 100644
--- a/rustfmt.toml
+++ b/rustfmt.toml
@@ -3,7 +3,7 @@ version = "Two"
 use_small_heuristics = "Max"
 merge_derives = false
 
-# Files to ignore. Each entry uses gitignore syntax.
+# Files to ignore. Each entry uses gitignore syntax, but `!` prefixes aren't allowed.
 ignore = [
     "/build/",
     "/*-build/",
@@ -12,13 +12,7 @@ ignore = [
 
     # Tests for now are not formatted, as they are sometimes pretty-printing constrained
     # (and generally rustfmt can move around comments in UI-testing incompatible ways).
-    "/tests/*",
-
-    # But we still want to format rmake.rs files in tests/run-make/ so we need to do this
-    # dance to avoid the parent directory from being excluded.
-    "!/tests/run-make/",
-    "/tests/run-make/*/*.rs",
-    "!/tests/run-make/*/rmake.rs",
+    "/tests/",
 
     # Do not format submodules.
     # FIXME: sync submodule list with tidy/bootstrap/etc
diff --git a/src/bootstrap/src/core/build_steps/format.rs b/src/bootstrap/src/core/build_steps/format.rs
index 7f9d88ca721..44f575b51da 100644
--- a/src/bootstrap/src/core/build_steps/format.rs
+++ b/src/bootstrap/src/core/build_steps/format.rs
@@ -115,8 +115,15 @@ pub fn format(build: &Builder<'_>, check: bool, paths: &[PathBuf]) {
     let rustfmt_config: RustfmtConfig = t!(toml::from_str(&rustfmt_config));
     let mut fmt_override = ignore::overrides::OverrideBuilder::new(&build.src);
     for ignore in rustfmt_config.ignore {
-        if let Some(ignore) = ignore.strip_prefix('!') {
-            fmt_override.add(ignore).expect(ignore);
+        if ignore.starts_with('!') {
+            // A `!`-prefixed entry could be added as a whitelisted entry in `fmt_override`, i.e.
+            // strip the `!` prefix. But as soon as whitelisted entries are added, an
+            // `OverrideBuilder` will only traverse those whitelisted entries, and won't traverse
+            // any files that aren't explicitly mentioned. No bueno! Maybe there's a way to combine
+            // explicit whitelisted entries and traversal of unmentioned files, but for now just
+            // forbid such entries.
+            eprintln!("`!`-prefixed entries are not supported in rustfmt.toml, sorry");
+            crate::exit!(1);
         } else {
             fmt_override.add(&format!("!{ignore}")).expect(&ignore);
         }