Rust 'rustfmt' cleanup

'rustfmt', by default, formats imports in a way that is prone to
 conflicts while merging and rebasing, since in some cases it condenses
 several items into the same line.
 
 Document in our guidelines that we will handle this for the moment with
 the trailing empty comment workaround and make the tree 'rustfmt'-clean
 again.
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Merge tag 'rust-rustfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux

Pull rustfmt fixes from Miguel Ojeda:
 "Rust 'rustfmt' cleanup

  'rustfmt', by default, formats imports in a way that is prone to
  conflicts while merging and rebasing, since in some cases it condenses
  several items into the same line.

  Document in our guidelines that we will handle this for the moment
  with the trailing empty comment workaround and make the tree
  'rustfmt'-clean again"

* tag 'rust-rustfmt' of git://git.kernel.org/pub/scm/linux/kernel/git/ojeda/linux:
  rust: bitmap: fix formatting
  rust: cpufreq: fix formatting
  rust: alloc: employ a trailing comment to keep vertical layout
  docs: rust: add section on imports formatting

Documentation/rust/coding-guidelines.rst

@@ -38,6 +38,81 @@ Like ``clang-format`` for the rest of the kernel, ``rustfmt`` works on
 individual files, and does not require a kernel configuration. Sometimes it may
 even work with broken code.
 
+Imports
+~~~~~~~
+
+``rustfmt``, by default, formats imports in a way that is prone to conflicts
+while merging and rebasing, since in some cases it condenses several items into
+the same line. For instance:
+
+.. code-block:: rust
+
+	// Do not use this style.
+	use crate::{
+	    example1,
+	    example2::{example3, example4, example5},
+	    example6, example7,
+	    example8::example9,
+	};
+
+Instead, the kernel uses a vertical layout that looks like this:
+
+.. code-block:: rust
+
+	use crate::{
+	    example1,
+	    example2::{
+	        example3,
+	        example4,
+	        example5, //
+	    },
+	    example6,
+	    example7,
+	    example8::example9, //
+	};
+
+That is, each item goes into its own line, and braces are used as soon as there
+is more than one item in a list.
+
+The trailing empty comment allows to preserve this formatting. Not only that,
+``rustfmt`` will actually reformat imports vertically when the empty comment is
+added. That is, it is possible to easily reformat the original example into the
+expected style by running ``rustfmt`` on an input like:
+
+.. code-block:: rust
+
+	// Do not use this style.
+	use crate::{
+	    example1,
+	    example2::{example3, example4, example5, //
+	    },
+	    example6, example7,
+	    example8::example9, //
+	};
+
+The trailing empty comment works for nested imports, as shown above, as well as
+for single item imports -- this can be useful to minimize diffs within patch
+series:
+
+.. code-block:: rust
+
+	use crate::{
+	    example1, //
+	};
+
+The trailing empty comment works in any of the lines within the braces, but it
+is preferred to keep it in the last item, since it is reminiscent of the
+trailing comma in other formatters. Sometimes it may be simpler to avoid moving
+the comment several times within a patch series due to changes in the list.
+
+There may be cases where exceptions may need to be made, i.e. none of this is
+a hard rule. There is also code that is not migrated to this style yet, but
+please do not introduce code in other styles.
+
+Eventually, the goal is to get ``rustfmt`` to support this formatting style (or
+a similar one) automatically in a stable release without requiring the trailing
+empty comment. Thus, at some point, the goal is to remove those comments.
+
 
 Comments
 --------

rust/kernel/alloc/kvec.rs

@@ -9,7 +9,7 @@ use super::{
 };
 use crate::{
     fmt,
-    page::AsPageIter,
+    page::AsPageIter, //
 };
 use core::{
     borrow::{Borrow, BorrowMut},

rust/kernel/bitmap.rs

@@ -167,7 +167,9 @@ impl core::ops::Deref for BitmapVec {
         let ptr = if self.nbits <= BITS_PER_LONG {
             // SAFETY: Bitmap is represented inline.
             #[allow(unused_unsafe, reason = "Safe since Rust 1.92.0")]
-            unsafe { core::ptr::addr_of!(self.repr.bitmap) }
+            unsafe {
+                core::ptr::addr_of!(self.repr.bitmap)
+            }
         } else {
             // SAFETY: Bitmap is represented as array of `unsigned long`.
             unsafe { self.repr.ptr.as_ptr() }
@@ -184,7 +186,9 @@ impl core::ops::DerefMut for BitmapVec {
         let ptr = if self.nbits <= BITS_PER_LONG {
             // SAFETY: Bitmap is represented inline.
             #[allow(unused_unsafe, reason = "Safe since Rust 1.92.0")]
-            unsafe { core::ptr::addr_of_mut!(self.repr.bitmap) }
+            unsafe {
+                core::ptr::addr_of_mut!(self.repr.bitmap)
+            }
         } else {
             // SAFETY: Bitmap is represented as array of `unsigned long`.
             unsafe { self.repr.ptr.as_ptr() }

rust/kernel/cpufreq.rs

@@ -38,8 +38,7 @@ use macros::vtable;
 const CPUFREQ_NAME_LEN: usize = bindings::CPUFREQ_NAME_LEN as usize;
 
 /// Default transition latency value in nanoseconds.
-pub const DEFAULT_TRANSITION_LATENCY_NS: u32 =
-        bindings::CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
+pub const DEFAULT_TRANSITION_LATENCY_NS: u32 = bindings::CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 /// CPU frequency driver flags.
 pub mod flags {