Use version-sorting for all sorting

Add a description of a version-sorting algorithm. (This algorithm does
not precisely match `strverscmp`; it's intentionally simpler in its
handling of leading zeroes, and produces a result easier for humans to
easily understand and do by hand.)

Change all references to sorting to use version-sorting.

Change all references to "ASCIIbetically" to instead say "sort
non-lowercase before lowercase".

src/doc/style-guide/src/README.md

@@ -99,6 +99,42 @@ fn bar() {}
 fn baz() {}
 ```
 
+### Sorting
+
+In various cases, the default Rust style specifies to sort things. If not
+otherwise specified, such sorting should be "version sorting", which ensures
+that (for instance) `x8` comes before `x16` even though the character `1` comes
+before the character `8`. (If not otherwise specified, version-sorting is
+lexicographical.)
+
+For the purposes of the Rust style, to compare two strings for version-sorting:
+
+- Compare the strings by (Unicode) character as normal, finding the index of
+  the first differing character. (If the two strings do not have the same
+  length, this may be the end of the shorter string.)
+- For both strings, determine the sequence of ASCII digits containing either
+  that character or the character before. (If either string doesn't have such a
+  sequence of ASCII digits, fall back to comparing the strings as normal.)
+- Compare the numeric values of the number specified by the sequence of digits.
+  (Note that an implementation of this algorithm can easily check this without
+  accumulating copies of the digits or converting to a number: longer sequences
+  of digits are larger numbers, equal-length sequences can be sorted
+  lexicographically.)
+- If the numbers have the same numeric value, the one with more leading zeroes
+  comes first.
+
+Note that there exist various algorithms called "version sorting", which differ
+most commonly in their handling of numbers with leading zeroes. This algorithm
+does not purport to precisely match the behavior of any particular other
+algorithm, only to produce a simple and satisfying result for Rust formatting.
+(In particular, this algorithm aims to produce a satisfying result for a set of
+symbols that have the same number of leading zeroes, and an acceptable and
+easily understandable result for a set of symbols that has varying numbers of
+leading zeroes.)
+
+As an example, version-sorting will sort the following symbols in the order
+given: `x000`, `x00`, `x0`, `x01`, `x1`, `x09`, `x9`, `x010`, `x10`.
+
 ### [Module-level items](items.md)
 
 ### [Statements](statements.md)

src/doc/style-guide/src/cargo.md

@@ -8,11 +8,11 @@ Put a blank line between the last key-value pair in a section and the header of
 the next section. Do not place a blank line between section headers and the
 key-value pairs in that section, or between key-value pairs in a section.
 
-Sort key names alphabetically within each section, with the exception of the
+Version-sort key names within each section, with the exception of the
 `[package]` section. Put the `[package]` section at the top of the file; put
 the `name` and `version` keys in that order at the top of that section,
-followed by the remaining keys other than `description` in alphabetical order,
-followed by the `description` at the end of that section.
+followed by the remaining keys other than `description` in order, followed by
+the `description` at the end of that section.
 
 Don't use quotes around any standard key names; use bare keys. Only use quoted
 keys for non-standard keys whose names require them, and avoid introducing such

src/doc/style-guide/src/editions.md

@@ -37,6 +37,8 @@ history of the style guide. Notable changes in the Rust 2024 style edition
 include:
 
 - Miscellaneous `rustfmt` bugfixes.
+- Use version-sort (sort `x8`, `x16`, `x32`, `x64`, `x128` in that order).
+- Change "ASCIIbetical" sort to Unicode-aware "non-lowercase before lowercase".
 
 ## Rust 2015/2018/2021 style edition
 

src/doc/style-guide/src/items.md

@@ -9,8 +9,8 @@ an item appears at module level or within another item.
 alphabetically.
 
 `use` statements, and module *declarations* (`mod foo;`, not `mod { ... }`)
-must come before other items. Put imports before module declarations. Sort each
-alphabetically, except that `self` and `super` must come before any other
+must come before other items. Put imports before module declarations.
+Version-sort each, except that `self` and `super` must come before any other
 names.
 
 Don't automatically move module declarations annotated with `#[macro_use]`,
@@ -441,8 +441,10 @@ foo::{
 A *group* of imports is a set of imports on the same or sequential lines. One or
 more blank lines or other items (e.g., a function) separate groups of imports.
 
-Within a group of imports, imports must be sorted ASCIIbetically (uppercase
-before lowercase). Groups of imports must not be merged or re-ordered.
+Within a group of imports, imports must be version-sorted, except that
+non-lowercase characters (characters that can start an `UpperCamelCase`
+identifier) must be sorted before lowercase characters. Groups of imports must
+not be merged or re-ordered.
 
 E.g., input:
 
@@ -469,10 +471,15 @@ re-ordering.
 
 ### Ordering list import
 
-Names in a list import must be sorted ASCIIbetically, but with `self` and
-`super` first, and groups and glob imports last. This applies recursively. For
-example, `a::*` comes before `b::a` but `a::b` comes before `a::*`. E.g.,
-`use foo::bar::{a, b::c, b::d, b::d::{x, y, z}, b::{self, r, s}};`.
+Names in a list import must be version-sorted, except that:
+- `self` and `super` always come first if present,
+- non-lowercase characters (characters that can start an `UpperCamelCase`
+  identifier) must be sorted before lowercase characters, and
+- groups and glob imports always come last if present.
+
+This applies recursively. For example, `a::*` comes before `b::a` but `a::b`
+comes before `a::*`. E.g., `use foo::bar::{a, b::c, b::d, b::d::{x, y, z},
+b::{self, r, s}};`.
 
 ### Normalisation