1 use crate::utils::paths;
3 is_expn_of, last_path_segment, match_def_path, match_type, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty,
5 use if_chain::if_chain;
7 use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
8 use rustc::{declare_lint_pass, declare_tool_lint};
9 use rustc_errors::Applicability;
10 use syntax::ast::LitKind;
11 use syntax::source_map::Span;
13 declare_clippy_lint! {
14 /// **What it does:** Checks for the use of `format!("string literal with no
15 /// argument")` and `format!("{}", foo)` where `foo` is a string.
17 /// **Why is this bad?** There is no point of doing that. `format!("foo")` can
18 /// be replaced by `"foo".to_owned()` if you really need a `String`. The even
19 /// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
20 /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
23 /// **Known problems:** None.
27 /// # let foo = "foo";
29 /// format!("{}", foo);
33 "useless use of `format!`"
36 declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
38 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessFormat {
39 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
40 let span = match is_expn_of(expr.span, "format") {
41 Some(s) if !s.from_expansion() => s,
45 // Operate on the only argument of `alloc::fmt::format`.
46 if let Some(sugg) = on_new_v1(cx, expr) {
47 span_useless_format(cx, span, "consider using .to_string()", sugg);
48 } else if let Some(sugg) = on_new_v1_fmt(cx, expr) {
49 span_useless_format(cx, span, "consider using .to_string()", sugg);
54 fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) {
55 let to_replace = span.source_callsite();
57 // The callsite span contains the statement semicolon for some reason.
58 let snippet = snippet(cx, to_replace, "..");
59 if snippet.ends_with(';') {
63 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
68 Applicability::MachineApplicable, // snippet
73 fn on_argumentv1_new<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr, arms: &'a [Arm]) -> Option<String> {
75 if let ExprKind::AddrOf(_, ref format_args) = expr.node;
76 if let ExprKind::Array(ref elems) = arms[0].body.node;
78 if let ExprKind::Call(ref fun, ref args) = elems[0].node;
79 if let ExprKind::Path(ref qpath) = fun.node;
80 if let Some(did) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
81 if match_def_path(cx, did, &paths::FMT_ARGUMENTV1_NEW);
82 // matches `core::fmt::Display::fmt`
84 if let ExprKind::Path(ref qpath) = args[1].node;
85 if let Some(did) = resolve_node(cx, qpath, args[1].hir_id).opt_def_id();
86 if match_def_path(cx, did, &paths::DISPLAY_FMT_METHOD);
87 // check `(arg0,)` in match block
88 if let PatKind::Tuple(ref pats, None) = arms[0].pat.node;
91 let ty = walk_ptrs_ty(cx.tables.pat_ty(&pats[0]));
92 if ty.sty != rustc::ty::Str && !match_type(cx, ty, &paths::STRING) {
95 if let ExprKind::Lit(ref lit) = format_args.node {
96 if let LitKind::Str(ref s, _) = lit.node {
97 return Some(format!("{:?}.to_string()", s.as_str()));
100 let snip = snippet(cx, format_args.span, "<arg>");
101 if let ExprKind::MethodCall(ref path, _, _) = format_args.node {
102 if path.ident.name == sym!(to_string) {
103 return Some(format!("{}", snip));
105 } else if let ExprKind::Binary(..) = format_args.node {
106 return Some(format!("{}", snip));
108 return Some(format!("{}.to_string()", snip));
115 fn on_new_v1<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<String> {
117 if let ExprKind::Call(ref fun, ref args) = expr.node;
119 if let ExprKind::Path(ref qpath) = fun.node;
120 if let Some(did) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
121 if match_def_path(cx, did, &paths::FMT_ARGUMENTS_NEW_V1);
122 // Argument 1 in `new_v1()`
123 if let ExprKind::AddrOf(_, ref arr) = args[0].node;
124 if let ExprKind::Array(ref pieces) = arr.node;
125 if pieces.len() == 1;
126 if let ExprKind::Lit(ref lit) = pieces[0].node;
127 if let LitKind::Str(ref s, _) = lit.node;
128 // Argument 2 in `new_v1()`
129 if let ExprKind::AddrOf(_, ref arg1) = args[1].node;
130 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.node;
132 if let ExprKind::Tup(ref tup) = matchee.node;
134 // `format!("foo")` expansion contains `match () { () => [], }`
136 return Some(format!("{:?}.to_string()", s.as_str()));
137 } else if s.as_str().is_empty() {
138 return on_argumentv1_new(cx, &tup[0], arms);
145 fn on_new_v1_fmt<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<String> {
147 if let ExprKind::Call(ref fun, ref args) = expr.node;
149 if let ExprKind::Path(ref qpath) = fun.node;
150 if let Some(did) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
151 if match_def_path(cx, did, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED);
152 if check_unformatted(&args[2]);
153 // Argument 1 in `new_v1_formatted()`
154 if let ExprKind::AddrOf(_, ref arr) = args[0].node;
155 if let ExprKind::Array(ref pieces) = arr.node;
156 if pieces.len() == 1;
157 if let ExprKind::Lit(ref lit) = pieces[0].node;
158 if let LitKind::Str(..) = lit.node;
159 // Argument 2 in `new_v1_formatted()`
160 if let ExprKind::AddrOf(_, ref arg1) = args[1].node;
161 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.node;
163 if let ExprKind::Tup(ref tup) = matchee.node;
165 return on_argumentv1_new(cx, &tup[0], arms);
171 /// Checks if the expression matches
175 /// width: _::Implied,
176 /// precision: _::Implied,
182 fn check_unformatted(expr: &Expr) -> bool {
184 if let ExprKind::AddrOf(_, ref expr) = expr.node;
185 if let ExprKind::Array(ref exprs) = expr.node;
187 // struct `core::fmt::rt::v1::Argument`
188 if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
189 if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym!(format));
190 // struct `core::fmt::rt::v1::FormatSpec`
191 if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
192 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym!(precision));
193 if let ExprKind::Path(ref precision_path) = precision_field.expr.node;
194 if last_path_segment(precision_path).ident.name == sym!(Implied);
195 if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym!(width));
196 if let ExprKind::Path(ref width_qpath) = width_field.expr.node;
197 if last_path_segment(width_qpath).ident.name == sym!(Implied);