1 use crate::utils::paths;
3 is_expn_of, is_type_diagnostic_item, last_path_segment, match_def_path, match_function_call, snippet, snippet_opt,
6 use if_chain::if_chain;
7 use rustc_ast::ast::LitKind;
8 use rustc_errors::Applicability;
9 use rustc_hir::{Arm, BorrowKind, Expr, ExprKind, MatchSource, PatKind};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::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.
31 /// # let foo = "foo";
32 /// format!("{}", foo);
39 "useless use of `format!`"
42 declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
44 impl<'tcx> LateLintPass<'tcx> for UselessFormat {
45 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
46 let span = match is_expn_of(expr.span, "format") {
47 Some(s) if !s.from_expansion() => s,
51 // Operate on the only argument of `alloc::fmt::format`.
52 if let Some(sugg) = on_new_v1(cx, expr) {
53 span_useless_format(cx, span, "consider using `.to_string()`", sugg);
54 } else if let Some(sugg) = on_new_v1_fmt(cx, expr) {
55 span_useless_format(cx, span, "consider using `.to_string()`", sugg);
60 fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) {
61 let to_replace = span.source_callsite();
63 // The callsite span contains the statement semicolon for some reason.
64 let snippet = snippet(cx, to_replace, "..");
65 if snippet.ends_with(';') {
69 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |diag| {
74 Applicability::MachineApplicable, // snippet
79 fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) -> Option<String> {
81 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref format_args) = expr.kind;
82 if let ExprKind::Array(ref elems) = arms[0].body.kind;
84 if let Some(args) = match_function_call(cx, &elems[0], &paths::FMT_ARGUMENTV1_NEW);
85 // matches `core::fmt::Display::fmt`
87 if let ExprKind::Path(ref qpath) = args[1].kind;
88 if let Some(did) = cx.qpath_res(qpath, args[1].hir_id).opt_def_id();
89 if match_def_path(cx, did, &paths::DISPLAY_FMT_METHOD);
90 // check `(arg0,)` in match block
91 if let PatKind::Tuple(ref pats, None) = arms[0].pat.kind;
94 let ty = cx.typeck_results().pat_ty(&pats[0]).peel_refs();
95 if *ty.kind() != rustc_middle::ty::Str && !is_type_diagnostic_item(cx, ty, sym::string_type) {
98 if let ExprKind::Lit(ref lit) = format_args.kind {
99 if let LitKind::Str(ref s, _) = lit.node {
100 return Some(format!("{:?}.to_string()", s.as_str()));
103 let snip = snippet(cx, format_args.span, "<arg>");
104 if let ExprKind::MethodCall(ref path, _, _, _) = format_args.kind {
105 if path.ident.name == sym!(to_string) {
106 return Some(format!("{}", snip));
108 } else if let ExprKind::Binary(..) = format_args.kind {
109 return Some(format!("{}", snip));
111 return Some(format!("{}.to_string()", snip));
118 fn on_new_v1<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
120 if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1);
122 // Argument 1 in `new_v1()`
123 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind;
124 if let ExprKind::Array(ref pieces) = arr.kind;
125 if pieces.len() == 1;
126 if let ExprKind::Lit(ref lit) = pieces[0].kind;
127 if let LitKind::Str(ref s, _) = lit.node;
128 // Argument 2 in `new_v1()`
129 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind;
130 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind;
132 if let ExprKind::Tup(ref tup) = matchee.kind;
134 // `format!("foo")` expansion contains `match () { () => [], }`
136 if let Some(s_src) = snippet_opt(cx, lit.span) {
137 // Simulate macro expansion, converting {{ and }} to { and }.
138 let s_expand = s_src.replace("{{", "{").replace("}}", "}");
139 return Some(format!("{}.to_string()", s_expand))
141 } else if s.as_str().is_empty() {
142 return on_argumentv1_new(cx, &tup[0], arms);
149 fn on_new_v1_fmt<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
151 if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED);
153 if check_unformatted(&args[2]);
154 // Argument 1 in `new_v1_formatted()`
155 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind;
156 if let ExprKind::Array(ref pieces) = arr.kind;
157 if pieces.len() == 1;
158 if let ExprKind::Lit(ref lit) = pieces[0].kind;
159 if let LitKind::Str(..) = lit.node;
160 // Argument 2 in `new_v1_formatted()`
161 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind;
162 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind;
164 if let ExprKind::Tup(ref tup) = matchee.kind;
166 return on_argumentv1_new(cx, &tup[0], arms);
172 /// Checks if the expression matches
176 /// width: _::Implied,
177 /// precision: _::Implied,
183 fn check_unformatted(expr: &Expr<'_>) -> bool {
185 if let ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) = expr.kind;
186 if let ExprKind::Array(ref exprs) = expr.kind;
188 // struct `core::fmt::rt::v1::Argument`
189 if let ExprKind::Struct(_, ref fields, _) = exprs[0].kind;
190 if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym::format);
191 // struct `core::fmt::rt::v1::FormatSpec`
192 if let ExprKind::Struct(_, ref fields, _) = format_field.expr.kind;
193 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym::precision);
194 if let ExprKind::Path(ref precision_path) = precision_field.expr.kind;
195 if last_path_segment(precision_path).ident.name == sym::Implied;
196 if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym::width);
197 if let ExprKind::Path(ref width_qpath) = width_field.expr.kind;
198 if last_path_segment(width_qpath).ident.name == sym::Implied;