Change None -> Preserve for group_imports config

Also reword configuration to be less specific.

Configurations.md

@@ -2010,20 +2010,15 @@ use sit;
 
 ## `group_imports`
 
-Discard existing import groups, and create three groups for:
-1. `std`, `core` and `alloc`,
-2. external crates,
-3. `self`, `super` and `crate` imports.
-
-Within each group, imports are sorted as with `reorder_imports`.
-
-This has no effect is `reorder_imports` is `false`.
+Controls the strategy for how imports are grouped together.
 
-- **Default value**: `None`
-- **Possible values**: `None`, `StdExternalCrate`
+- **Default value**: `Preserve`
+- **Possible values**: `Preserve`, `StdExternalCrate`
 - **Stable**: No
 
-#### `None` (default):
+#### `Preserve` (default):
+
+Preserve the source file's import groups.
 
 ```rust
 use super::update::convert_publish_payload;
@@ -2044,6 +2039,11 @@ use core::f32;
 
 #### `StdExternalCrate`:
 
+Discard existing import groups, and create three groups for:
+1. `std`, `core` and `alloc`,
+2. external crates,
+3. `self`, `super` and `crate` imports.
+
 ```rust
 use alloc::alloc::Layout;
 use core::f32;

src/config.rs

@@ -78,7 +78,7 @@ create_config! {
     imports_indent: IndentStyle, IndentStyle::Block, false, "Indent of imports";
     imports_layout: ListTactic, ListTactic::Mixed, false, "Item layout inside a import block";
     merge_imports: bool, false, false, "Merge imports";
-    group_imports: GroupImportsTactic, GroupImportsTactic::None, false,
+    group_imports: GroupImportsTactic, GroupImportsTactic::Preserve, false,
         "Reorganize import groups";
 
     // Ordering
@@ -595,7 +595,7 @@ where_single_line = false
 imports_indent = "Block"
 imports_layout = "Mixed"
 merge_imports = false
-group_imports = "None"
+group_imports = "Preserve"
 reorder_imports = true
 reorder_modules = true
 reorder_impl_items = false

src/config/options.rs

@@ -110,7 +110,7 @@ impl Density {
 /// Configuration for import groups, i.e. sets of imports separated by newlines.
 pub enum GroupImportsTactic {
     /// Keep groups as they are.
-    None,
+    Preserve,
     /// Discard existing groups, and create new groups for
     ///  1. `std` / `core` / `alloc` imports
     ///  2. other imports

src/formatting/reorder.rs

@@ -195,7 +195,7 @@ fn rewrite_reorderable_item(
 
 /// Rewrite a list of items with reordering and/or regrouping. Every item
 /// in `items` must have the same `ast::ItemKind`. Whether reordering, regrouping,
-/// or both ore done is determined from the `context`.
+/// or both are done is determined from the `context`.
 fn rewrite_reorderable_or_regroupable_items(
     context: &RewriteContext<'_>,
     reorderable_items: &[&ast::Item],
@@ -230,11 +230,9 @@ fn rewrite_reorderable_or_regroupable_items(
                 normalized_items = merge_use_trees(normalized_items);
             }
 
-            let mut regrouped_items = if context.config.group_imports() != GroupImportsTactic::None
-            {
-                group_imports(normalized_items)
-            } else {
-                vec![normalized_items]
+            let mut regrouped_items = match context.config.group_imports() {
+                GroupImportsTactic::Preserve => vec![normalized_items],
+                GroupImportsTactic::StdExternalCrate => group_imports(normalized_items),
             };
 
             if context.config.reorder_imports() {
@@ -363,14 +361,14 @@ impl ReorderableItemKind {
             ReorderableItemKind::ExternCrate
             | ReorderableItemKind::Mod
             | ReorderableItemKind::Other => false,
-            ReorderableItemKind::Use => config.group_imports() != GroupImportsTactic::None,
+            ReorderableItemKind::Use => config.group_imports() != GroupImportsTactic::Preserve,
         }
     }
 
     fn in_group(self, config: &Config) -> bool {
         match self {
             ReorderableItemKind::ExternCrate | ReorderableItemKind::Mod => true,
-            ReorderableItemKind::Use => config.group_imports() == GroupImportsTactic::None,
+            ReorderableItemKind::Use => config.group_imports() == GroupImportsTactic::Preserve,
             ReorderableItemKind::Other => false,
         }
     }