125 lines
4.6 KiB
Rust
125 lines
4.6 KiB
Rust
use rustc::hir::*;
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use rustc::lint::*;
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use rustc::ty;
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use syntax::ast::LitKind;
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use utils::paths;
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use utils::{is_expn_of, match_def_path, match_type, opt_def_id, resolve_node, snippet, span_lint_and_then, walk_ptrs_ty};
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/// **What it does:** Checks for the use of `format!("string literal with no
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/// argument")` and `format!("{}", foo)` where `foo` is a string.
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///
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/// **Why is this bad?** There is no point of doing that. `format!("too")` can
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/// be replaced by `"foo".to_owned()` if you really need a `String`. The even
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/// worse `&format!("foo")` is often encountered in the wild. `format!("{}",
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/// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()`
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/// if `foo: &str`.
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///
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/// **Known problems:** None.
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///
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/// **Examples:**
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/// ```rust
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/// format!("foo")
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/// format!("{}", foo)
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/// ```
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declare_lint! {
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pub USELESS_FORMAT,
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Warn,
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"useless use of `format!`"
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}
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#[derive(Copy, Clone, Debug)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array![USELESS_FORMAT]
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
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if let Some(span) = is_expn_of(expr.span, "format") {
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match expr.node {
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// `format!("{}", foo)` expansion
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ExprCall(ref fun, ref args) => {
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if_chain! {
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if let ExprPath(ref qpath) = fun.node;
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if args.len() == 2;
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if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, fun.hir_id));
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if match_def_path(cx.tcx, fun_def_id, &paths::FMT_ARGUMENTS_NEWV1);
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// ensure the format string is `"{..}"` with only one argument and no text
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if check_static_str(&args[0]);
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// ensure the format argument is `{}` ie. Display with no fancy option
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// and that the argument is a string
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if check_arg_is_display(cx, &args[1]);
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then {
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let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
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span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
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db.span_suggestion(expr.span, "consider using .to_string()", sugg);
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});
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}
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}
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},
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// `format!("foo")` expansion contains `match () { () => [], }`
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ExprMatch(ref matchee, _, _) => if let ExprTup(ref tup) = matchee.node {
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if tup.is_empty() {
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let sugg = format!("{}.to_string()", snippet(cx, expr.span, "<expr>").into_owned());
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span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |db| {
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db.span_suggestion(span, "consider using .to_string()", sugg);
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});
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}
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},
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_ => (),
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}
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}
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}
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}
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/// Checks if the expressions matches `&[""]`
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fn check_static_str(expr: &Expr) -> bool {
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if_chain! {
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if let ExprAddrOf(_, ref expr) = expr.node; // &[""]
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if let ExprArray(ref exprs) = expr.node; // [""]
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if exprs.len() == 1;
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if let ExprLit(ref lit) = exprs[0].node;
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if let LitKind::Str(ref lit, _) = lit.node;
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then {
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return lit.as_str().is_empty();
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}
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}
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false
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}
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/// Checks if the expressions matches
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/// ```rust,ignore
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/// &match (&42,) {
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/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0,
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/// ::std::fmt::Display::fmt)],
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/// }
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/// ```
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fn check_arg_is_display(cx: &LateContext, expr: &Expr) -> bool {
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if_chain! {
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if let ExprAddrOf(_, ref expr) = expr.node;
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if let ExprMatch(_, ref arms, _) = expr.node;
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if arms.len() == 1;
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if arms[0].pats.len() == 1;
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if let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node;
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if pat.len() == 1;
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if let ExprArray(ref exprs) = arms[0].body.node;
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if exprs.len() == 1;
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if let ExprCall(_, ref args) = exprs[0].node;
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if args.len() == 2;
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if let ExprPath(ref qpath) = args[1].node;
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if let Some(fun_def_id) = opt_def_id(resolve_node(cx, qpath, args[1].hir_id));
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if match_def_path(cx.tcx, fun_def_id, &paths::DISPLAY_FMT_METHOD);
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then {
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let ty = walk_ptrs_ty(cx.tables.pat_ty(&pat[0]));
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return ty.sty == ty::TyStr || match_type(cx, ty, &paths::STRING);
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}
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}
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false
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}
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