1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::paths;
3 use clippy_utils::source::{snippet, snippet_opt};
4 use clippy_utils::sugg::Sugg;
5 use clippy_utils::ty::is_type_diagnostic_item;
6 use clippy_utils::{is_expn_of, last_path_segment, match_def_path, match_function_call};
7 use if_chain::if_chain;
8 use rustc_ast::ast::LitKind;
9 use rustc_errors::Applicability;
10 use rustc_hir::{Arm, BorrowKind, Expr, ExprKind, MatchSource, PatKind};
11 use rustc_lint::{LateContext, LateLintPass, LintContext};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Span;
16 declare_clippy_lint! {
17 /// **What it does:** Checks for the use of `format!("string literal with no
18 /// argument")` and `format!("{}", foo)` where `foo` is a string.
20 /// **Why is this bad?** There is no point of doing that. `format!("foo")` can
21 /// be replaced by `"foo".to_owned()` if you really need a `String`. The even
22 /// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
23 /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
26 /// **Known problems:** None.
33 /// format!("{}", foo);
40 "useless use of `format!`"
43 declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
45 impl<'tcx> LateLintPass<'tcx> for UselessFormat {
46 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
47 let span = match is_expn_of(expr.span, "format") {
48 Some(s) if !s.from_expansion() => s,
52 // Operate on the only argument of `alloc::fmt::format`.
53 if let Some(sugg) = on_new_v1(cx, expr) {
54 span_useless_format(cx, span, "consider using `.to_string()`", sugg);
55 } else if let Some(sugg) = on_new_v1_fmt(cx, expr) {
56 span_useless_format(cx, span, "consider using `.to_string()`", sugg);
61 fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) {
62 let to_replace = span.source_callsite();
64 // The callsite span contains the statement semicolon for some reason.
65 let snippet = snippet(cx, to_replace, "..");
66 if snippet.ends_with(';') {
70 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |diag| {
75 Applicability::MachineApplicable, // snippet
80 fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) -> Option<String> {
82 if let ExprKind::AddrOf(BorrowKind::Ref, _, format_args) = expr.kind;
83 if let ExprKind::Array(elems) = arms[0].body.kind;
85 if let Some(args) = match_function_call(cx, &elems[0], &paths::FMT_ARGUMENTV1_NEW);
86 // matches `core::fmt::Display::fmt`
88 if let ExprKind::Path(ref qpath) = args[1].kind;
89 if let Some(did) = cx.qpath_res(qpath, args[1].hir_id).opt_def_id();
90 if match_def_path(cx, did, &paths::DISPLAY_FMT_METHOD);
91 // check `(arg0,)` in match block
92 if let PatKind::Tuple(pats, None) = arms[0].pat.kind;
95 let ty = cx.typeck_results().pat_ty(pats[0]).peel_refs();
96 if *ty.kind() != rustc_middle::ty::Str && !is_type_diagnostic_item(cx, ty, sym::string_type) {
99 if let ExprKind::Lit(ref lit) = format_args.kind {
100 if let LitKind::Str(ref s, _) = lit.node {
101 return Some(format!("{:?}.to_string()", s.as_str()));
104 let sugg = Sugg::hir(cx, format_args, "<arg>");
105 if let ExprKind::MethodCall(path, _, _, _) = format_args.kind {
106 if path.ident.name == sym!(to_string) {
107 return Some(format!("{}", sugg));
109 } else if let ExprKind::Binary(..) = format_args.kind {
110 return Some(format!("{}", sugg));
112 return Some(format!("{}.to_string()", sugg.maybe_par()));
119 fn on_new_v1<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
121 if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1);
123 // Argument 1 in `new_v1()`
124 if let ExprKind::AddrOf(BorrowKind::Ref, _, arr) = args[0].kind;
125 if let ExprKind::Array(pieces) = arr.kind;
126 if pieces.len() == 1;
127 if let ExprKind::Lit(ref lit) = pieces[0].kind;
128 if let LitKind::Str(ref s, _) = lit.node;
129 // Argument 2 in `new_v1()`
130 if let ExprKind::AddrOf(BorrowKind::Ref, _, arg1) = args[1].kind;
131 if let ExprKind::Match(matchee, arms, MatchSource::Normal) = arg1.kind;
133 if let ExprKind::Tup(tup) = matchee.kind;
135 // `format!("foo")` expansion contains `match () { () => [], }`
137 if let Some(s_src) = snippet_opt(cx, lit.span) {
138 // Simulate macro expansion, converting {{ and }} to { and }.
139 let s_expand = s_src.replace("{{", "{").replace("}}", "}");
140 return Some(format!("{}.to_string()", s_expand));
142 } else if s.as_str().is_empty() {
143 return on_argumentv1_new(cx, &tup[0], arms);
150 fn on_new_v1_fmt<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> {
152 if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED);
154 if check_unformatted(&args[2]);
155 // Argument 1 in `new_v1_formatted()`
156 if let ExprKind::AddrOf(BorrowKind::Ref, _, arr) = args[0].kind;
157 if let ExprKind::Array(pieces) = arr.kind;
158 if pieces.len() == 1;
159 if let ExprKind::Lit(ref lit) = pieces[0].kind;
160 if let LitKind::Str(..) = lit.node;
161 // Argument 2 in `new_v1_formatted()`
162 if let ExprKind::AddrOf(BorrowKind::Ref, _, arg1) = args[1].kind;
163 if let ExprKind::Match(matchee, arms, MatchSource::Normal) = arg1.kind;
165 if let ExprKind::Tup(tup) = matchee.kind;
167 return on_argumentv1_new(cx, &tup[0], arms);
173 /// Checks if the expression matches
177 /// width: _::Implied,
178 /// precision: _::Implied,
184 fn check_unformatted(expr: &Expr<'_>) -> bool {
186 if let ExprKind::AddrOf(BorrowKind::Ref, _, expr) = expr.kind;
187 if let ExprKind::Array(exprs) = expr.kind;
189 // struct `core::fmt::rt::v1::Argument`
190 if let ExprKind::Struct(_, fields, _) = exprs[0].kind;
191 if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym::format);
192 // struct `core::fmt::rt::v1::FormatSpec`
193 if let ExprKind::Struct(_, fields, _) = format_field.expr.kind;
194 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym::precision);
195 if let ExprKind::Path(ref precision_path) = precision_field.expr.kind;
196 if last_path_segment(precision_path).ident.name == sym::Implied;
197 if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym::width);
198 if let ExprKind::Path(ref width_qpath) = width_field.expr.kind;
199 if last_path_segment(width_qpath).ident.name == sym::Implied;