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1 | use crate::utils::paths; |
2 | use crate::utils::{ | |
3 | is_expn_of, is_type_diagnostic_item, last_path_segment, match_def_path, match_function_call, snippet, snippet_opt, | |
4 | span_lint_and_then, | |
5 | }; | |
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; | |
13 | use rustc_span::sym; | |
14 | ||
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. | |
18 | /// | |
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()` | |
23 | /// if `foo: &str`. | |
24 | /// | |
25 | /// **Known problems:** None. | |
26 | /// | |
27 | /// **Examples:** | |
28 | /// ```rust | |
29 | /// | |
30 | /// // Bad | |
31 | /// let foo = "foo"; | |
32 | /// format!("{}", foo); | |
33 | /// | |
34 | /// // Good | |
35 | /// foo.to_owned(); | |
36 | /// ``` | |
37 | pub USELESS_FORMAT, | |
38 | complexity, | |
39 | "useless use of `format!`" | |
40 | } | |
41 | ||
42 | declare_lint_pass!(UselessFormat => [USELESS_FORMAT]); | |
43 | ||
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, | |
48 | _ => return, | |
49 | }; | |
50 | ||
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); | |
56 | } | |
57 | } | |
58 | } | |
59 | ||
60 | fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) { | |
61 | let to_replace = span.source_callsite(); | |
62 | ||
63 | // The callsite span contains the statement semicolon for some reason. | |
64 | let snippet = snippet(cx, to_replace, ".."); | |
65 | if snippet.ends_with(';') { | |
66 | sugg.push(';'); | |
67 | } | |
68 | ||
69 | span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |diag| { | |
70 | diag.span_suggestion( | |
71 | to_replace, | |
72 | help, | |
73 | sugg, | |
74 | Applicability::MachineApplicable, // snippet | |
75 | ); | |
76 | }); | |
77 | } | |
78 | ||
79 | fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) -> Option<String> { | |
80 | if_chain! { | |
81 | if let ExprKind::AddrOf(BorrowKind::Ref, _, ref format_args) = expr.kind; | |
82 | if let ExprKind::Array(ref elems) = arms[0].body.kind; | |
83 | if elems.len() == 1; | |
84 | if let Some(args) = match_function_call(cx, &elems[0], &paths::FMT_ARGUMENTV1_NEW); | |
85 | // matches `core::fmt::Display::fmt` | |
86 | if args.len() == 2; | |
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; | |
92 | if pats.len() == 1; | |
93 | then { | |
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) { | |
96 | return None; | |
97 | } | |
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())); | |
101 | } | |
102 | } else { | |
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)); | |
107 | } | |
108 | } else if let ExprKind::Binary(..) = format_args.kind { | |
109 | return Some(format!("{}", snip)); | |
110 | } | |
111 | return Some(format!("{}.to_string()", snip)); | |
112 | } | |
113 | } | |
114 | } | |
115 | None | |
116 | } | |
117 | ||
118 | fn on_new_v1<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> { | |
119 | if_chain! { | |
120 | if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1); | |
121 | if args.len() == 2; | |
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; | |
131 | if arms.len() == 1; | |
132 | if let ExprKind::Tup(ref tup) = matchee.kind; | |
133 | then { | |
134 | // `format!("foo")` expansion contains `match () { () => [], }` | |
135 | if tup.is_empty() { | |
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)) | |
140 | } | |
141 | } else if s.as_str().is_empty() { | |
142 | return on_argumentv1_new(cx, &tup[0], arms); | |
143 | } | |
144 | } | |
145 | } | |
146 | None | |
147 | } | |
148 | ||
149 | fn on_new_v1_fmt<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> { | |
150 | if_chain! { | |
151 | if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED); | |
152 | if args.len() == 3; | |
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; | |
163 | if arms.len() == 1; | |
164 | if let ExprKind::Tup(ref tup) = matchee.kind; | |
165 | then { | |
166 | return on_argumentv1_new(cx, &tup[0], arms); | |
167 | } | |
168 | } | |
169 | None | |
170 | } | |
171 | ||
172 | /// Checks if the expression matches | |
173 | /// ```rust,ignore | |
174 | /// &[_ { | |
175 | /// format: _ { | |
176 | /// width: _::Implied, | |
177 | /// precision: _::Implied, | |
178 | /// ... | |
179 | /// }, | |
180 | /// ..., | |
181 | /// }] | |
182 | /// ``` | |
183 | fn check_unformatted(expr: &Expr<'_>) -> bool { | |
184 | if_chain! { | |
185 | if let ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) = expr.kind; | |
186 | if let ExprKind::Array(ref exprs) = expr.kind; | |
187 | if exprs.len() == 1; | |
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; | |
199 | then { | |
200 | return true; | |
201 | } | |
202 | } | |
203 | ||
204 | false | |
205 | } |