use rustc::hir::*; use rustc::lint::*; use rustc::ty; use syntax::ast::LitKind; use syntax_pos::Span; use crate::utils::paths; use crate::utils::{in_macro, is_expn_of, last_path_segment, match_def_path, match_type, opt_def_id, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty}; /// **What it does:** Checks for the use of `format!("string literal with no /// argument")` and `format!("{}", foo)` where `foo` is a string. /// /// **Why is this bad?** There is no point of doing that. `format!("too")` can /// be replaced by `"foo".to_owned()` if you really need a `String`. The even /// worse `&format!("foo")` is often encountered in the wild. `format!("{}", /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()` /// if `foo: &str`. /// /// **Known problems:** None. /// /// **Examples:** /// ```rust /// format!("foo") /// format!("{}", foo) /// ``` declare_clippy_lint! { pub USELESS_FORMAT, complexity, "useless use of `format!`" } #[derive(Copy, Clone, Debug)] pub struct Pass; impl LintPass for Pass { fn get_lints(&self) -> LintArray { lint_array![USELESS_FORMAT] } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let Some(span) = is_expn_of(expr.span, "format") { if in_macro(span) { return; } match expr.node { // `format!("{}", foo)` expansion ExprCall(ref fun, ref args) => { if_chain! { if let ExprPath(ref qpath) = fun.node; if args.len() == 3; if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, fun.hir_id)); if match_def_path(cx.tcx, fun_def_id, &paths::FMT_ARGUMENTS_NEWV1FORMATTED); if check_single_piece(&args[0]); if let Some(format_arg) = get_single_string_arg(cx, &args[1]); if check_unformatted(&args[2]); then { let sugg = format!("{}.to_string()", snippet(cx, format_arg, "").into_owned()); span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| { db.span_suggestion(expr.span, "consider using .to_string()", sugg); }); } } }, // `format!("foo")` expansion contains `match () { () => [], }` ExprMatch(ref matchee, _, _) => if let ExprTup(ref tup) = matchee.node { if tup.is_empty() { let sugg = format!("{}.to_string()", snippet(cx, expr.span, "").into_owned()); span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| { db.span_suggestion(span, "consider using .to_string()", sugg); }); } }, _ => (), } } } } /// Checks if the expressions matches `&[""]` fn check_single_piece(expr: &Expr) -> bool { if_chain! { if let ExprAddrOf(_, ref expr) = expr.node; // &[""] if let ExprArray(ref exprs) = expr.node; // [""] if exprs.len() == 1; if let ExprLit(ref lit) = exprs[0].node; if let LitKind::Str(ref lit, _) = lit.node; then { return lit.as_str().is_empty(); } } false } /// Checks if the expressions matches /// ```rust,ignore /// &match (&"arg",) { /// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0, /// ::std::fmt::Display::fmt)], /// } /// ``` /// and that type of `__arg0` is `&str` or `String` /// then returns the span of first element of the matched tuple fn get_single_string_arg(cx: &LateContext, expr: &Expr) -> Option { if_chain! { if let ExprAddrOf(_, ref expr) = expr.node; if let ExprMatch(ref match_expr, ref arms, _) = expr.node; if arms.len() == 1; if arms[0].pats.len() == 1; if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node; if pat.len() == 1; if let ExprArray(ref exprs) = arms[0].body.node; if exprs.len() == 1; if let ExprCall(_, ref args) = exprs[0].node; if args.len() == 2; if let ExprPath(ref qpath) = args[1].node; if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, args[1].hir_id)); if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD); then { let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0])); if ty.sty == ty::TyStr || match_type(cx, ty, &paths::STRING) { if let ExprTup(ref values) = match_expr.node { return Some(values[0].span); } } } } None } /// Checks if the expression matches /// ```rust,ignore /// &[_ { /// format: _ { /// width: _::Implied, /// ... /// }, /// ..., /// }] /// ``` fn check_unformatted(expr: &Expr) -> bool { if_chain! { if let ExprAddrOf(_, ref expr) = expr.node; if let ExprArray(ref exprs) = expr.node; if exprs.len() == 1; if let ExprStruct(_, ref fields, _) = exprs[0].node; if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format"); if let ExprStruct(_, ref fields, _) = format_field.expr.node; if let Some(align_field) = fields.iter().find(|f| f.ident.name == "width"); if let ExprPath(ref qpath) = align_field.expr.node; if last_path_segment(qpath).name == "Implied"; then { return true; } } false }