1 use crate::utils::paths;
4 in_macro_or_desugar, is_expn_of, last_path_segment, match_def_path, match_type, resolve_node, snippet,
5 span_lint_and_then, walk_ptrs_ty,
7 use if_chain::if_chain;
9 use rustc::lint::{LateContext, LateLintPass, LintArray, LintContext, LintPass};
11 use rustc::{declare_lint_pass, declare_tool_lint};
12 use rustc_errors::Applicability;
13 use syntax::ast::LitKind;
14 use syntax::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.
31 /// format!("{}", foo)
35 "useless use of `format!`"
38 declare_lint_pass!(UselessFormat => [USELESS_FORMAT]);
40 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UselessFormat {
41 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
42 if let Some(span) = is_expn_of(expr.span, *sym::format) {
43 if in_macro_or_desugar(span) {
47 // `format!("{}", foo)` expansion
48 ExprKind::Call(ref fun, ref args) => {
50 if let ExprKind::Path(ref qpath) = fun.node;
51 if let Some(fun_def_id) = resolve_node(cx, qpath, fun.hir_id).opt_def_id();
52 let new_v1 = match_def_path(cx, fun_def_id, &*paths::FMT_ARGUMENTS_NEWV1);
53 let new_v1_fmt = match_def_path(cx,
55 &*paths::FMT_ARGUMENTS_NEWV1FORMATTED
57 if new_v1 || new_v1_fmt;
58 if check_single_piece(&args[0]);
59 if let Some(format_arg) = get_single_string_arg(cx, &args[1]);
60 if new_v1 || check_unformatted(&args[2]);
61 if let ExprKind::AddrOf(_, ref format_arg) = format_arg.node;
63 let (message, sugg) = if_chain! {
64 if let ExprKind::MethodCall(ref path, _, _) = format_arg.node;
65 if path.ident.as_interned_str() == "to_string";
67 ("`to_string()` is enough",
68 snippet(cx, format_arg.span, "<arg>").to_string())
70 ("consider using .to_string()",
71 format!("{}.to_string()", snippet(cx, format_arg.span, "<arg>")))
75 span_useless_format(cx, span, message, sugg);
79 // `format!("foo")` expansion contains `match () { () => [], }`
80 ExprKind::Match(ref matchee, _, _) => {
81 if let ExprKind::Tup(ref tup) = matchee.node {
83 let actual_snippet = snippet(cx, expr.span, "<expr>").to_string();
84 let actual_snippet = actual_snippet.replace("{{}}", "{}");
85 let sugg = format!("{}.to_string()", actual_snippet);
86 span_useless_format(cx, span, "consider using .to_string()", sugg);
96 fn span_useless_format<'a, 'tcx: 'a, T: LintContext<'tcx>>(cx: &'a T, span: Span, help: &str, mut sugg: String) {
97 let to_replace = span.source_callsite();
99 // The callsite span contains the statement semicolon for some reason.
100 let snippet = snippet(cx, to_replace, "..");
101 if snippet.ends_with(';') {
105 span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
110 Applicability::MachineApplicable, // snippet
115 /// Checks if the expressions matches `&[""]`
116 fn check_single_piece(expr: &Expr) -> bool {
118 if let ExprKind::AddrOf(_, ref expr) = expr.node; // &[""]
119 if let ExprKind::Array(ref exprs) = expr.node; // [""]
121 if let ExprKind::Lit(ref lit) = exprs[0].node;
122 if let LitKind::Str(ref lit, _) = lit.node;
124 return lit.as_str().is_empty();
131 /// Checks if the expressions matches
133 /// &match (&"arg",) {
134 /// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
135 /// ::std::fmt::Display::fmt)],
138 /// and that the type of `__arg0` is `&str` or `String`,
139 /// then returns the span of first element of the matched tuple.
140 fn get_single_string_arg<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr) -> Option<&'a Expr> {
142 if let ExprKind::AddrOf(_, ref expr) = expr.node;
143 if let ExprKind::Match(ref match_expr, ref arms, _) = expr.node;
145 if arms[0].pats.len() == 1;
146 if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
148 if let ExprKind::Array(ref exprs) = arms[0].body.node;
150 if let ExprKind::Call(_, ref args) = exprs[0].node;
152 if let ExprKind::Path(ref qpath) = args[1].node;
153 if let Some(fun_def_id) = resolve_node(cx, qpath, args[1].hir_id).opt_def_id();
154 if match_def_path(cx, fun_def_id, &*paths::DISPLAY_FMT_METHOD);
156 let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
157 if ty.sty == ty::Str || match_type(cx, ty, &*paths::STRING) {
158 if let ExprKind::Tup(ref values) = match_expr.node {
159 return Some(&values[0]);
168 /// Checks if the expression matches
172 /// width: _::Implied,
178 fn check_unformatted(expr: &Expr) -> bool {
180 if let ExprKind::AddrOf(_, ref expr) = expr.node;
181 if let ExprKind::Array(ref exprs) = expr.node;
183 if let ExprKind::Struct(_, ref fields, _) = exprs[0].node;
184 if let Some(format_field) = fields.iter().find(|f| f.ident.name == *sym::format);
185 if let ExprKind::Struct(_, ref fields, _) = format_field.expr.node;
186 if let Some(width_field) = fields.iter().find(|f| f.ident.name == *sym::width);
187 if let ExprKind::Path(ref width_qpath) = width_field.expr.node;
188 if last_path_segment(width_qpath).ident.name == *sym::Implied;
189 if let Some(precision_field) = fields.iter().find(|f| f.ident.name == *sym::precision);
190 if let ExprKind::Path(ref precision_path) = precision_field.expr.node;
191 if last_path_segment(precision_path).ident.name == *sym::Implied;