Add support for edition 2021.

Author: m-ou-se

Configurations.md

@@ -569,7 +569,7 @@ fn main() {
 Specifies which edition is used by the parser.
 
 - **Default value**: `"2015"`
-- **Possible values**: `"2015"`, `"2018"`
+- **Possible values**: `"2015"`, `"2018"`, `"2021"`
 - **Stable**: Yes
 
 Rustfmt is able to pick up the edition used by reading the `Cargo.toml` file if executed

src/config/options.rs

@@ -343,6 +343,10 @@ pub enum Edition {
     #[doc_hint = "2018"]
     /// Edition 2018.
     Edition2018,
+    #[value = "2021"]
+    #[doc_hint = "2021"]
+    /// Edition 2021.
+    Edition2021,
 }
 
 impl Default for Edition {
@@ -356,10 +360,17 @@ impl From<Edition> for rustc_span::edition::Edition {
         match edition {
             Edition::Edition2015 => Self::Edition2015,
             Edition::Edition2018 => Self::Edition2018,
+            Edition::Edition2021 => Self::Edition2021,
         }
     }
 }
 
+impl PartialOrd for Edition {
+    fn partial_cmp(&self, other: &Edition) -> Option<std::cmp::Ordering> {
+        rustc_span::edition::Edition::partial_cmp(&(*self).into(), &(*other).into())
+    }
+}
+
 /// Controls how rustfmt should handle leading pipes on match arms.
 #[config_type]
 pub enum MatchArmLeadingPipe {

src/formatting/imports.rs

@@ -333,7 +333,7 @@ impl UseTree {
         };
 
         let leading_modsep =
-            context.config.edition() == Edition::Edition2018 && a.prefix.is_global();
+            context.config.edition() >= Edition::Edition2018 && a.prefix.is_global();
 
         let mut modsep = leading_modsep;