use proc_macro2::{Delimiter, Group, TokenStream, TokenTree}; use std::mem; use syn::visit_mut::{self, VisitMut}; use syn::{Expr, File, Generics, LifetimeParam, MacroDelimiter, Stmt, StmtMacro, TypeParam}; pub struct FlattenParens; impl FlattenParens { pub fn visit_token_stream_mut(tokens: &mut TokenStream) { *tokens = mem::take(tokens) .into_iter() .flat_map(|tt| { if let TokenTree::Group(group) = tt { let delimiter = group.delimiter(); let mut content = group.stream(); Self::visit_token_stream_mut(&mut content); if let Delimiter::Parenthesis = delimiter { content } else { TokenStream::from(TokenTree::Group(Group::new(delimiter, content))) } } else { TokenStream::from(tt) } }) .collect(); } } impl VisitMut for FlattenParens { fn visit_expr_mut(&mut self, e: &mut Expr) { while let Expr::Paren(paren) = e { *e = mem::replace(&mut *paren.expr, Expr::PLACEHOLDER); } visit_mut::visit_expr_mut(self, e); } } pub struct AsIfPrinted; impl VisitMut for AsIfPrinted { fn visit_file_mut(&mut self, file: &mut File) { file.shebang = None; visit_mut::visit_file_mut(self, file); } fn visit_generics_mut(&mut self, generics: &mut Generics) { if generics.params.is_empty() { generics.lt_token = None; generics.gt_token = None; } if let Some(where_clause) = &generics.where_clause { if where_clause.predicates.is_empty() { generics.where_clause = None; } } visit_mut::visit_generics_mut(self, generics); } fn visit_lifetime_param_mut(&mut self, param: &mut LifetimeParam) { if param.bounds.is_empty() { param.colon_token = None; } visit_mut::visit_lifetime_param_mut(self, param); } fn visit_stmt_mut(&mut self, stmt: &mut Stmt) { if let Stmt::Expr(expr, semi) = stmt { if let Expr::Macro(e) = expr { if match e.mac.delimiter { MacroDelimiter::Brace(_) => true, MacroDelimiter::Paren(_) | MacroDelimiter::Bracket(_) => semi.is_some(), } { let Expr::Macro(expr) = mem::replace(expr, Expr::PLACEHOLDER) else { unreachable!(); }; *stmt = Stmt::Macro(StmtMacro { attrs: expr.attrs, mac: expr.mac, semi_token: *semi, }); } } } visit_mut::visit_stmt_mut(self, stmt); } fn visit_type_param_mut(&mut self, param: &mut TypeParam) { if param.bounds.is_empty() { param.colon_token = None; } visit_mut::visit_type_param_mut(self, param); } }