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 if arms[0].pats.len() == 1;
88 // check `(arg0,)` in match block
89 if let PatKind::Tuple(ref pats, None) = arms[0].pats[0].node;
92 let ty = walk_ptrs_ty(cx.tables.pat_ty(&pats[0]));
93 if ty.sty != rustc::ty::Str && !match_type(cx, ty, &paths::STRING) {
96 if let ExprKind::Lit(ref lit) = format_args.node {
97 if let LitKind::Str(ref s, _) = lit.node {
98 return Some(format!("{:?}.to_string()", s.as_str()));
101 let snip = snippet(cx, format_args.span, "<arg>");
102 if let ExprKind::MethodCall(ref path, _, _) = format_args.node {
103 if path.ident.name == sym!(to_string) {
104 return Some(format!("{}", snip));
106 } else if let ExprKind::Binary(..) = format_args.node {
107 return Some(format!("{}", snip));
109 return Some(format!("{}.to_string()", snip));
116 fn on_new_v1<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<String> {
118 if let ExprKind::Call(ref fun, ref args) = expr.node;
120 if let ExprKind::Path(ref qpath) = fun.node;
121 if let Some(did) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
122 if match_def_path(cx, did, &paths::FMT_ARGUMENTS_NEW_V1);
123 // Argument 1 in `new_v1()`
124 if let ExprKind::AddrOf(_, ref arr) = args[0].node;
125 if let ExprKind::Array(ref pieces) = arr.node;
126 if pieces.len() == 1;
127 if let ExprKind::Lit(ref lit) = pieces[0].node;
128 if let LitKind::Str(ref s, _) = lit.node;
129 // Argument 2 in `new_v1()`
130 if let ExprKind::AddrOf(_, ref arg1) = args[1].node;
131 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.node;
133 if let ExprKind::Tup(ref tup) = matchee.node;
135 // `format!("foo")` expansion contains `match () { () => [], }`
137 return Some(format!("{:?}.to_string()", s.as_str()));
138 } else if s.as_str().is_empty() {
139 return on_argumentv1_new(cx, &tup[0], arms);
146 fn on_new_v1_fmt<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) -> Option<String> {
148 if let ExprKind::Call(ref fun, ref args) = expr.node;
150 if let ExprKind::Path(ref qpath) = fun.node;
151 if let Some(did) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
152 if match_def_path(cx, did, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED);
153 if check_unformatted(&args[2]);
154 // Argument 1 in `new_v1_formatted()`
155 if let ExprKind::AddrOf(_, ref arr) = args[0].node;
156 if let ExprKind::Array(ref pieces) = arr.node;
157 if pieces.len() == 1;
158 if let ExprKind::Lit(ref lit) = pieces[0].node;
159 if let LitKind::Str(..) = lit.node;
160 // Argument 2 in `new_v1_formatted()`
161 if let ExprKind::AddrOf(_, ref arg1) = args[1].node;
162 if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.node;
164 if let ExprKind::Tup(ref tup) = matchee.node;
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(_, ref expr) = expr.node;
186 if let ExprKind::Array(ref exprs) = expr.node;
188 // struct `core::fmt::rt::v1::Argument`
189 if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
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.node;
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.node;
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.node;
198 if last_path_segment(width_qpath).ident.name == sym!(Implied);