1 use crate::utils::paths;
3 in_macro, is_expn_of, last_path_segment, 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};
9 use rustc::{declare_lint_pass, declare_tool_lint};
10 use rustc_errors::Applicability;
11 use syntax::ast::LitKind;
12 use syntax::source_map::Span;
14 declare_clippy_lint! {
15 /// **What it does:** Checks for the use of `format!("string literal with no
16 /// argument")` and `format!("{}", foo)` where `foo` is a string.
18 /// **Why is this bad?** There is no point of doing that. `format!("foo")` can
19 /// be replaced by `"foo".to_owned()` if you really need a `String`. The even
20 /// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
21 /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
24 /// **Known problems:** None.
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 if let Some(span) = is_expn_of(expr.span, "format") {
45 // `format!("{}", foo)` expansion
46 ExprKind::Call(ref fun, ref args) => {
48 if let ExprKind::Path(ref qpath) = fun.node;
49 if let Some(fun_def_id) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
50 let new_v1 = cx.match_def_path(fun_def_id, &paths::FMT_ARGUMENTS_NEWV1);
51 let new_v1_fmt = cx.match_def_path(
53 &paths::FMT_ARGUMENTS_NEWV1FORMATTED
55 if new_v1 || new_v1_fmt;
56 if check_single_piece(&args[0]);
57 if let Some(format_arg) = get_single_string_arg(cx, &args[1]);
58 if new_v1 || check_unformatted(&args[2]);
59 if let ExprKind::AddrOf(_, ref format_arg) = format_arg.node;
61 let (message, sugg) = if_chain! {
62 if let ExprKind::MethodCall(ref path, _, _) = format_arg.node;
63 if path.ident.as_interned_str() == "to_string";
65 ("`to_string()` is enough",
66 snippet(cx, format_arg.span, "<arg>").to_string())
68 ("consider using .to_string()",
69 format!("{}.to_string()", snippet(cx, format_arg.span, "<arg>")))
73 span_useless_format(cx, span, message, sugg);
77 // `format!("foo")` expansion contains `match () { () => [], }`
78 ExprKind::Match(ref matchee, _, _) => {
79 if let ExprKind::Tup(ref tup) = matchee.node {
81 let actual_snippet = snippet(cx, expr.span, "<expr>").to_string();
82 let actual_snippet = actual_snippet.replace("{{}}", "{}");
83 let sugg = format!("{}.to_string()", actual_snippet);
84 span_useless_format(cx, span, "consider using .to_string()", sugg);
94 fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) {
95 let to_replace = span.source_callsite();
97 // The callsite span contains the statement semicolon for some reason.
98 let snippet = snippet(cx, to_replace, "..");
99 if snippet.ends_with(';') {
103 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
108 Applicability::MachineApplicable, // snippet
113 /// Checks if the expressions matches `&[""]`
114 fn check_single_piece(expr: &Expr) -> bool {
116 if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""]
117 if let ExprKind::Array(ref exprs) = expr.node; // [""]
119 if let ExprKind::Lit(ref lit) = exprs[0].node;
120 if let LitKind::Str(ref lit, _) = lit.node;
122 return lit.as_str().is_empty();
129 /// Checks if the expressions matches
131 /// &match (&"arg",) {
132 /// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
133 /// ::std::fmt::Display::fmt)],
136 /// and that the type of `__arg0` is `&str` or `String`,
137 /// then returns the span of first element of the matched tuple.
138 fn get_single_string_arg<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<&'a Expr> {
140 if let ExprKind::AddrOf(_, ref expr) = expr.node;
141 if let ExprKind::Match(ref match_expr, ref arms, _) = expr.node;
143 if arms[0].pats.len() == 1;
144 if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
146 if let ExprKind::Array(ref exprs) = arms[0].body.node;
148 if let ExprKind::Call(_, ref args) = exprs[0].node;
150 if let ExprKind::Path(ref qpath) = args[1].node;
151 if let Some(fun_def_id) = resolve_node(cx, qpath, args[1].hir_id).opt_def_id();
152 if cx.match_def_path(fun_def_id, &paths::DISPLAY_FMT_METHOD);
154 let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
155 if ty.sty == ty::Str || match_type(cx, ty, &paths::STRING) {
156 if let ExprKind::Tup(ref values) = match_expr.node {
157 return Some(&values[0]);
166 /// Checks if the expression matches
170 /// width: _::Implied,
176 fn check_unformatted(expr: &Expr) -> bool {
178 if let ExprKind::AddrOf(_, ref expr) = expr.node;
179 if let ExprKind::Array(ref exprs) = expr.node;
181 if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
182 if let Some(format_field) = fields.iter().find(|f| f.ident.name == "format");
183 if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
184 if let Some(width_field) = fields.iter().find(|f| f.ident.name == "width");
185 if let ExprKind::Path(ref width_qpath) = width_field.expr.node;
186 if last_path_segment(width_qpath).ident.name == "Implied";
187 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == "precision");
188 if let ExprKind::Path(ref precision_path) = precision_field.expr.node;
189 if last_path_segment(precision_path).ident.name == "Implied";