2 use rustc::hir::map::Node::NodeItem;
4 use rustc::ty::TypeVariants;
5 use syntax::ast::LitKind;
7 use utils::{is_expn_of, match_def_path, match_type, resolve_node, span_lint, walk_ptrs_ty};
9 /// **What it does:** Checks for the use of `format!("string literal with no
10 /// argument")` and `format!("{}", foo)` where `foo` is a string.
12 /// **Why is this bad?** There is no point of doing that. `format!("too")` can
13 /// be replaced by `"foo".to_owned()` if you really need a `String`. The even
14 /// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
15 /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
18 /// **Known problems:** None.
23 /// format!("{}", foo)
28 "useless use of `format!`"
31 #[derive(Copy, Clone, Debug)]
34 impl LintPass for Pass {
35 fn get_lints(&self) -> LintArray {
36 lint_array![USELESS_FORMAT]
40 impl LateLintPass for Pass {
41 fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
42 if let Some(span) = is_expn_of(cx, expr.span, "format") {
44 // `format!("{}", foo)` expansion
45 ExprCall(ref fun, ref args) => {
47 let ExprPath(..) = fun.node,
49 let Some(fun) = resolve_node(cx, fun.id),
50 match_def_path(cx, fun.def_id(), &paths::FMT_ARGUMENTS_NEWV1),
51 // ensure the format string is `"{..}"` with only one argument and no text
52 check_static_str(cx, &args[0]),
53 // ensure the format argument is `{}` ie. Display with no fancy option
54 check_arg_is_display(cx, &args[1])
56 span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
59 // `format!("foo")` expansion contains `match () { () => [], }`
60 ExprMatch(ref matchee, _, _) => {
61 if let ExprTup(ref tup) = matchee.node {
63 span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
73 /// Returns the slice of format string parts in an `Arguments::new_v1` call.
74 /// Public because it's shared with a lint in print.rs.
75 pub fn get_argument_fmtstr_parts<'a, 'b>(cx: &LateContext<'a, 'b>, expr: &'a Expr)
76 -> Option<Vec<&'a str>> {
78 let ExprBlock(ref block) = expr.node,
79 block.stmts.len() == 1,
80 let StmtDecl(ref decl, _) = block.stmts[0].node,
81 let DeclItem(ref decl) = decl.node,
82 let Some(NodeItem(decl)) = cx.tcx.map.find(decl.id),
83 decl.name.as_str() == "__STATIC_FMTSTR",
84 let ItemStatic(_, _, ref expr) = decl.node,
85 let ExprAddrOf(_, ref expr) = expr.node, // &["…", "…", …]
86 let ExprArray(ref exprs) = expr.node,
88 let mut result = Vec::new();
90 if let ExprLit(ref lit) = expr.node {
91 if let LitKind::Str(ref lit, _) = lit.node {
101 /// Checks if the expressions matches
103 /// { static __STATIC_FMTSTR: … = &["…", "…", …]; __STATIC_FMTSTR }
105 fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
106 if let Some(expr) = get_argument_fmtstr_parts(cx, expr) {
107 expr.len() == 1 && expr[0].is_empty()
113 /// Checks if the expressions matches
116 /// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0, ::std::fmt::Display::fmt)],
119 fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
121 let ExprAddrOf(_, ref expr) = expr.node,
122 let ExprMatch(_, ref arms, _) = expr.node,
124 arms[0].pats.len() == 1,
125 let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node,
127 let ExprArray(ref exprs) = arms[0].body.node,
129 let ExprCall(_, ref args) = exprs[0].node,
131 let ExprPath(None, _) = args[1].node,
132 let Some(fun) = resolve_node(cx, args[1].id),
133 match_def_path(cx, fun.def_id(), &paths::DISPLAY_FMT_METHOD),
135 let ty = walk_ptrs_ty(cx.tcx.tables().pat_ty(&pat[0]));
137 return ty.sty == TypeVariants::TyStr || match_type(cx, ty, &paths::STRING);