Mark HasSource::source_old as deprecated but allow at all call sites

crates/completion/src/render/const_.rs

@@ -27,6 +27,7 @@ struct ConstRender<'a> {
 
 impl<'a> ConstRender<'a> {
     fn new(ctx: RenderContext<'a>, const_: hir::Const) -> ConstRender<'a> {
+        #[allow(deprecated)]
         let ast_node = const_.source_old(ctx.db()).value;
         ConstRender { ctx, const_, ast_node }
     }

crates/completion/src/render/function.rs

@@ -34,6 +34,7 @@ impl<'a> FunctionRender<'a> {
         fn_: hir::Function,
     ) -> FunctionRender<'a> {
         let name = local_name.unwrap_or_else(|| fn_.name(ctx.db()).to_string());
+        #[allow(deprecated)]
         let ast_node = fn_.source_old(ctx.db()).value;
 
         FunctionRender { ctx, name, func: fn_, ast_node }

crates/completion/src/render/macro_.rs

@@ -96,6 +96,7 @@ impl<'a> MacroRender<'a> {
     }
 
     fn detail(&self) -> String {
+        #[allow(deprecated)]
         let ast_node = self.macro_.source_old(self.ctx.db()).value;
         macro_label(&ast_node)
     }

crates/completion/src/render/type_alias.rs

@@ -27,6 +27,7 @@ struct TypeAliasRender<'a> {
 
 impl<'a> TypeAliasRender<'a> {
     fn new(ctx: RenderContext<'a>, type_alias: hir::TypeAlias) -> TypeAliasRender<'a> {
+        #[allow(deprecated)]
         let ast_node = type_alias.source_old(ctx.db()).value;
         TypeAliasRender { ctx, type_alias, ast_node }
     }