use crate::utils::paths; use crate::utils::{ in_macro, is_expn_of, last_path_segment, match_type, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty, }; use if_chain::if_chain; use rustc::hir::*; use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass}; use rustc::ty; use rustc::{declare_lint_pass, declare_tool_lint}; use rustc_errors::Applicability; use syntax::ast::LitKind; use syntax::source_map::Span; declare_clippy_lint! { /// **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!("foo")` 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) /// ``` pub USELESS_FORMAT, complexity, "useless use of `format!`" } declare_lint_pass!(UselessFormat => [USELESS_FORMAT]); impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessFormat { 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 ExprKind::Call(ref fun, ref args) => { if_chain! { if let ExprKind::Path(ref qpath) = fun.node; if let Some(fun_def_id) = resolve_node(cx, qpath, fun.hir_id).opt_def_id(); let new_v1 = cx.match_def_path(fun_def_id, &paths::FMT_ARGUMENTS_NEWV1); let new_v1_fmt = cx.match_def_path( fun_def_id, &paths::FMT_ARGUMENTS_NEWV1FORMATTED ); if new_v1 || new_v1_fmt; if check_single_piece(&args[0]); if let Some(format_arg) = get_single_string_arg(cx, &args[1]); if new_v1 || check_unformatted(&args[2]); if let ExprKind::AddrOf(_, ref format_arg) = format_arg.node; then { let (message, sugg) = if_chain! { if let ExprKind::MethodCall(ref path, _, _) = format_arg.node; if path.ident.as_interned_str() == "to_string"; then { ("`to_string()` is enough", snippet(cx, format_arg.span, "").to_string()) } else { ("consider using .to_string()", format!("{}.to_string()", snippet(cx, format_arg.span, ""))) } }; span_useless_format(cx, span, message, sugg); } } }, // `format!("foo")` expansion contains `match () { () => [], }` ExprKind::Match(ref matchee, _, _) => { if let ExprKind::Tup(ref tup) = matchee.node { if tup.is_empty() { let actual_snippet = snippet(cx, expr.span, "").to_string(); let actual_snippet = actual_snippet.replace("{{}}", "{}"); let sugg = format!("{}.to_string()", actual_snippet); span_useless_format(cx, span, "consider using .to_string()", sugg); } } }, _ => (), } } } } fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) { let to_replace = span.source_callsite(); // The callsite span contains the statement semicolon for some reason. let snippet = snippet(cx, to_replace, ".."); if snippet.ends_with(';') { sugg.push(';'); } span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| { db.span_suggestion( to_replace, help, sugg, Applicability::MachineApplicable, // snippet ); }); } /// Checks if the expressions matches `&[""]` fn check_single_piece(expr: &Expr) -> bool { if_chain! { if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""] if let ExprKind::Array(ref exprs) = expr.node; // [""] if exprs.len() == 1; if let ExprKind::Lit(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 the type of `__arg0` is `&str` or `String`, /// then returns the span of first element of the matched tuple. fn get_single_string_arg<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<&'a Expr> { if_chain! { if let ExprKind::AddrOf(_, ref expr) = expr.node; if let ExprKind::Match(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 ExprKind::Array(ref exprs) = arms[0].body.node; if exprs.len() == 1; if let ExprKind::Call(_, ref args) = exprs[0].node; if args.len() == 2; if let ExprKind::Path(ref qpath) = args[1].node; if let Some(fun_def_id) = resolve_node(cx, qpath, args[1].hir_id).opt_def_id(); if cx.match_def_path(fun_def_id, &paths::DISPLAY_FMT_METHOD); then { let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0])); if ty.sty == ty::Str || match_type(cx, ty, &paths::STRING) { if let ExprKind::Tup(ref values) = match_expr.node { return Some(&values[0]); } } } } None } /// Checks if the expression matches /// ```rust,ignore /// &[_ { /// format: _ { /// width: _::Implied, /// ... /// }, /// ..., /// }] /// ``` fn check_unformatted(expr: &Expr) -> bool { if_chain! { if let ExprKind::AddrOf(_, ref expr) = expr.node; if let ExprKind::Array(ref exprs) = expr.node; if exprs.len() == 1; if let ExprKind::Struct(_, ref fields, _) = exprs[0].node; if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format"); if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node; if let Some(width_field) = fields.iter().find(|f| f.ident.name == "width"); if let ExprKind::Path(ref width_qpath) = width_field.expr.node; if last_path_segment(width_qpath).ident.name == "Implied"; if let Some(precision_field) = fields.iter().find(|f| f.ident.name == "precision"); if let ExprKind::Path(ref precision_path) = precision_field.expr.node; if last_path_segment(precision_path).ident.name == "Implied"; then { return true; } } false }