1 use crate::utils::paths;
3 in_macro, is_expn_of, last_path_segment, match_def_path, match_type, opt_def_id, resolve_node, snippet,
4 span_lint_and_then, walk_ptrs_ty,
6 use if_chain::if_chain;
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
10 use rustc::{declare_tool_lint, lint_array};
11 use rustc_errors::Applicability;
12 use syntax::ast::LitKind;
13 use syntax::source_map::Span;
15 declare_clippy_lint! {
16 /// **What it does:** Checks for the use of `format!("string literal with no
17 /// argument")` and `format!("{}", foo)` where `foo` is a string.
19 /// **Why is this bad?** There is no point of doing that. `format!("foo")` can
20 /// be replaced by `"foo".to_owned()` if you really need a `String`. The even
21 /// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
22 /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
25 /// **Known problems:** None.
30 /// format!("{}", foo)
34 "useless use of `format!`"
37 #[derive(Copy, Clone, Debug)]
40 impl LintPass for Pass {
41 fn get_lints(&self) -> LintArray {
42 lint_array![USELESS_FORMAT]
45 fn name(&self) -> &'static str {
50 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
51 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
52 if let Some(span) = is_expn_of(expr.span, "format") {
57 // `format!("{}", foo)` expansion
58 ExprKind::Call(ref fun, ref args) => {
60 if let ExprKind::Path(ref qpath) = fun.node;
61 if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, fun.hir_id));
62 let new_v1 = match_def_path(cx.tcx, fun_def_id, &paths::FMT_ARGUMENTS_NEWV1);
63 let new_v1_fmt = match_def_path(
66 &paths::FMT_ARGUMENTS_NEWV1FORMATTED
68 if new_v1 || new_v1_fmt;
69 if check_single_piece(&args[0]);
70 if let Some(format_arg) = get_single_string_arg(cx, &args[1]);
71 if new_v1 || check_unformatted(&args[2]);
72 if let ExprKind::AddrOf(_, ref format_arg) = format_arg.node;
74 let (message, sugg) = if_chain! {
75 if let ExprKind::MethodCall(ref path, _, _) = format_arg.node;
76 if path.ident.as_interned_str() == "to_string";
78 ("`to_string()` is enough",
79 snippet(cx, format_arg.span, "<arg>").to_string())
81 ("consider using .to_string()",
82 format!("{}.to_string()", snippet(cx, format_arg.span, "<arg>")))
86 span_useless_format(cx, span, message, sugg);
90 // `format!("foo")` expansion contains `match () { () => [], }`
91 ExprKind::Match(ref matchee, _, _) => {
92 if let ExprKind::Tup(ref tup) = matchee.node {
94 let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
95 span_useless_format(cx, span, "consider using .to_string()", sugg);
105 fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) {
106 let to_replace = span.source_callsite();
108 // The callsite span contains the statement semicolon for some reason.
109 let snippet = snippet(cx, to_replace, "..");
110 if snippet.ends_with(';') {
114 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
119 Applicability::MachineApplicable, // snippet
124 /// Checks if the expressions matches `&[""]`
125 fn check_single_piece(expr: &Expr) -> bool {
127 if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""]
128 if let ExprKind::Array(ref exprs) = expr.node; // [""]
130 if let ExprKind::Lit(ref lit) = exprs[0].node;
131 if let LitKind::Str(ref lit, _) = lit.node;
133 return lit.as_str().is_empty();
140 /// Checks if the expressions matches
142 /// &match (&"arg",) {
143 /// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
144 /// ::std::fmt::Display::fmt)],
147 /// and that the type of `__arg0` is `&str` or `String`,
148 /// then returns the span of first element of the matched tuple.
149 fn get_single_string_arg<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<&'a Expr> {
151 if let ExprKind::AddrOf(_, ref expr) = expr.node;
152 if let ExprKind::Match(ref match_expr, ref arms, _) = expr.node;
154 if arms[0].pats.len() == 1;
155 if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
157 if let ExprKind::Array(ref exprs) = arms[0].body.node;
159 if let ExprKind::Call(_, ref args) = exprs[0].node;
161 if let ExprKind::Path(ref qpath) = args[1].node;
162 if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, args[1].hir_id));
163 if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD);
165 let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
166 if ty.sty == ty::Str || match_type(cx, ty, &paths::STRING) {
167 if let ExprKind::Tup(ref values) = match_expr.node {
168 return Some(&values[0]);
177 /// Checks if the expression matches
181 /// width: _::Implied,
187 fn check_unformatted(expr: &Expr) -> bool {
189 if let ExprKind::AddrOf(_, ref expr) = expr.node;
190 if let ExprKind::Array(ref exprs) = expr.node;
192 if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
193 if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format");
194 if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
195 if let Some(width_field) = fields.iter().find(|f| f.ident.name == "width");
196 if let ExprKind::Path(ref width_qpath) = width_field.expr.node;
197 if last_path_segment(width_qpath).ident.name == "Implied";
198 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == "precision");
199 if let ExprKind::Path(ref precision_path) = precision_field.expr.node;
200 if last_path_segment(precision_path).ident.name == "Implied";