Move gen and 'static in the keyword list.

- `gen` is an edition-specific keyword used in unstable Rust, and so
  belongs with `try` (as `is_unused_keyword_conditional` indicates).

- `'static` is a weak keyword according to the Reference and the
  Ferrocene spec, and so belongs with the other weak keywords.

- The cases in `is_unused_keyword_conditional` should be in alphabetical
  order, to match the keyword list.

None of these changes affect the behaviour of any of the `Symbol::is_*`
functions.

Author: nnethercote

compiler/rustc_span/src/symbol.rs

@@ -88,21 +88,19 @@ symbols! {
         Dyn:                "dyn", // >= 2018 Edition only
 
         // Edition-specific keywords that are used in unstable Rust or reserved for future use.
+        Gen:                "gen", // >= 2024 Edition only
         Try:                "try", // >= 2018 Edition only
 
-        // Special lifetime names
-        StaticLifetime:     "'static",
-
         // Weak keywords, have special meaning only in specific contexts.
         Auto:               "auto",
         Builtin:            "builtin",
         Catch:              "catch",
         Default:            "default",
-        Gen:                "gen",
         MacroRules:         "macro_rules",
         Raw:                "raw",
         Reuse:              "reuse",
         Safe:               "safe",
+        StaticLifetime:     "'static",
         Union:              "union",
         Yeet:               "yeet",
     }
@@ -2608,8 +2606,8 @@ impl Symbol {
     }
 
     fn is_unused_keyword_conditional(self, edition: impl Copy + FnOnce() -> Edition) -> bool {
-        self == kw::Try && edition().at_least_rust_2018()
-            || self == kw::Gen && edition().at_least_rust_2024()
+        self == kw::Gen && edition().at_least_rust_2024()
+            || self == kw::Try && edition().at_least_rust_2018()
     }
 
     pub fn is_reserved(self, edition: impl Copy + FnOnce() -> Edition) -> bool {