Add gen modifier to functions

We don't yet lower or maybe even parse them, but blocks already have `gen`, so why not.

crates/ide-assists/src/handlers/extract_function.rs

@@ -1617,6 +1617,7 @@ fn format_function(
         fun.control_flow.is_async,
         fun.mods.is_const,
         fun.control_flow.is_unsafe,
+        false,
     )
 }
 

crates/ide-assists/src/handlers/generate_delegate_methods.rs

@@ -122,6 +122,7 @@ pub(crate) fn generate_delegate_methods(acc: &mut Assists, ctx: &AssistContext<'
                 let is_async = method_source.async_token().is_some();
                 let is_const = method_source.const_token().is_some();
                 let is_unsafe = method_source.unsafe_token().is_some();
+                let is_gen = method_source.gen_token().is_some();
 
                 let fn_name = make::name(&name);
 
@@ -154,6 +155,7 @@ pub(crate) fn generate_delegate_methods(acc: &mut Assists, ctx: &AssistContext<'
                     is_async,
                     is_const,
                     is_unsafe,
+                    is_gen,
                 )
                 .clone_for_update();
 

crates/ide-assists/src/handlers/generate_delegate_trait.rs

@@ -740,6 +740,7 @@ fn func_assoc_item(
         item.async_token().is_some(),
         item.const_token().is_some(),
         item.unsafe_token().is_some(),
+        item.gen_token().is_some(),
     )
     .clone_for_update();
 

crates/ide-assists/src/handlers/generate_function.rs

@@ -365,6 +365,7 @@ impl FunctionBuilder {
             self.is_async,
             false, // FIXME : const and unsafe are not handled yet.
             false,
+            false,
         )
         .clone_for_update();
 

crates/ide-assists/src/handlers/generate_getter_or_setter.rs

@@ -261,7 +261,19 @@ fn generate_getter_from_info(
     let ret_type = Some(make::ret_type(ty));
     let body = make::block_expr([], Some(body));
 
-    make::fn_(strukt.visibility(), fn_name, None, None, params, body, ret_type, false, false, false)
+    make::fn_(
+        strukt.visibility(),
+        fn_name,
+        None,
+        None,
+        params,
+        body,
+        ret_type,
+        false,
+        false,
+        false,
+        false,
+    )
 }
 
 fn generate_setter_from_info(info: &AssistInfo, record_field_info: &RecordFieldInfo) -> ast::Fn {
@@ -285,7 +297,19 @@ fn generate_setter_from_info(info: &AssistInfo, record_field_info: &RecordFieldI
     let body = make::block_expr([assign_stmt.into()], None);
 
     // Make the setter fn
-    make::fn_(strukt.visibility(), fn_name, None, None, params, body, None, false, false, false)
+    make::fn_(
+        strukt.visibility(),
+        fn_name,
+        None,
+        None,
+        params,
+        body,
+        None,
+        false,
+        false,
+        false,
+        false,
+    )
 }
 
 fn extract_and_parse(

crates/ide-assists/src/handlers/generate_new.rs

@@ -115,6 +115,7 @@ pub(crate) fn generate_new(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option
             false,
             false,
             false,
+            false,
         )
         .clone_for_update();
         fn_.indent(1.into());

crates/syntax/rust.ungram

@@ -186,7 +186,7 @@ UseTreeList =
 
 Fn =
  Attr* Visibility?
- 'default'? 'const'? 'async'? 'unsafe'? Abi?
+ 'default'? 'const'? 'async'? 'gen'? 'unsafe'? Abi?
  'fn' Name GenericParamList? ParamList RetType? WhereClause?
  (body:BlockExpr | ';')
 

crates/syntax/src/ast/generated/nodes.rs

@@ -484,6 +484,8 @@ impl Fn {
     #[inline]
     pub fn fn_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![fn]) }
     #[inline]
+    pub fn gen_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![gen]) }
+    #[inline]
     pub fn unsafe_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![unsafe]) }
 }
 

crates/syntax/src/ast/make.rs

@@ -1035,6 +1035,7 @@ pub fn fn_(
     is_async: bool,
     is_const: bool,
     is_unsafe: bool,
+    is_gen: bool,
 ) -> ast::Fn {
     let type_params = match type_params {
         Some(type_params) => format!("{type_params}"),
@@ -1056,9 +1057,10 @@ pub fn fn_(
     let async_literal = if is_async { "async " } else { "" };
     let const_literal = if is_const { "const " } else { "" };
     let unsafe_literal = if is_unsafe { "unsafe " } else { "" };
+    let gen_literal = if is_gen { "gen " } else { "" };
 
     ast_from_text(&format!(
-        "{visibility}{async_literal}{const_literal}{unsafe_literal}fn {fn_name}{type_params}{params} {ret_type}{where_clause}{body}",
+        "{visibility}{const_literal}{async_literal}{gen_literal}{unsafe_literal}fn {fn_name}{type_params}{params} {ret_type}{where_clause}{body}",
     ))
 }
 pub fn struct_(