mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-29 22:43:41 +00:00
119 lines
4.1 KiB
Rust
119 lines
4.1 KiB
Rust
use rustc::hir::*;
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use rustc::hir::map::Node::NodeItem;
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use rustc::lint::*;
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use rustc::ty::TypeVariants;
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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_path, match_type, span_lint, walk_ptrs_ty};
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/// **What it does:** This lints about use of `format!("string literal with no argument")` and
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/// `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 be replaced by `"foo".to_owned()` if you really need a `String`. The even worse `&format!("foo")` is often
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/// encountered in the wild. `format!("{}", foo)` can be replaced by `foo.clone()` if `foo: String`
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/// or `foo.to_owned()` is `foo: &str`.
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///
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/// **Known problems:** None.
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///
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/// **Examples:** `format!("foo")` and `format!("{}", foo)`
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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 LateLintPass for Pass {
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fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
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if let Some(span) = is_expn_of(cx, 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_let_chain!{[
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let ExprPath(_, ref path) = fun.node,
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args.len() == 2,
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match_path(path, &paths::FMT_ARGUMENTS_NEWV1),
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// ensure the format string is `"{..}"` with only one argument and no text
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check_static_str(cx, &args[0]),
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// ensure the format argument is `{}` ie. Display with no fancy option
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check_arg_is_display(cx, &args[1])
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], {
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span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
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}}
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}
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// `format!("foo")` expansion contains `match () { () => [], }`
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ExprMatch(ref matchee, _, _) => {
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if let ExprTup(ref tup) = matchee.node {
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if tup.is_empty() {
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span_lint(cx, USELESS_FORMAT, span, "useless use of `format!`");
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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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/// ```
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/// { static __STATIC_FMTSTR: &[""] = _; __STATIC_FMTSTR }
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/// ```
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fn check_static_str(cx: &LateContext, expr: &Expr) -> bool {
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if_let_chain! {[
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let ExprBlock(ref block) = expr.node,
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block.stmts.len() == 1,
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let StmtDecl(ref decl, _) = block.stmts[0].node,
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let DeclItem(ref decl) = decl.node,
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let Some(NodeItem(decl)) = cx.tcx.map.find(decl.id),
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decl.name.as_str() == "__STATIC_FMTSTR",
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let ItemStatic(_, _, ref expr) = decl.node,
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let ExprAddrOf(_, ref expr) = expr.node, // &[""]
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let ExprVec(ref expr) = expr.node,
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expr.len() == 1,
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let ExprLit(ref lit) = expr[0].node,
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let LitKind::Str(ref lit, _) = lit.node,
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lit.is_empty()
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], {
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return true;
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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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/// ```
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/// &match (&42,) {
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/// (__arg0,) => [::std::fmt::ArgumentV1::new(__arg0, ::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_let_chain! {[
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let ExprAddrOf(_, ref expr) = expr.node,
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let ExprMatch(_, ref arms, _) = expr.node,
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arms.len() == 1,
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arms[0].pats.len() == 1,
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let PatKind::Tuple(ref pat, None) = arms[0].pats[0].node,
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pat.len() == 1,
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let ExprVec(ref exprs) = arms[0].body.node,
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exprs.len() == 1,
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let ExprCall(_, ref args) = exprs[0].node,
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args.len() == 2,
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let ExprPath(None, ref path) = args[1].node,
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match_path(path, &paths::DISPLAY_FMT_METHOD)
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], {
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let ty = walk_ptrs_ty(cx.tcx.pat_ty(&pat[0]));
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return ty.sty == TypeVariants::TyStr || match_type(cx, ty, &paths::STRING);
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}}
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false
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}
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