142 lines
4.9 KiB
Rust
142 lines
4.9 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_def_path, match_type, resolve_node, span_lint, 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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/// is `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 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(..) = fun.node,
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args.len() == 2,
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let Some(fun) = resolve_node(cx, fun.id),
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match_def_path(cx, 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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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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/// Returns the slice of format string parts in an `Arguments::new_v1` call.
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/// Public because it's shared with a lint in print.rs.
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pub fn get_argument_fmtstr_parts<'a, 'b>(cx: &LateContext<'a, 'b>, expr: &'a Expr)
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-> Option<Vec<&'a str>> {
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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 ExprArray(ref exprs) = expr.node,
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], {
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let mut result = Vec::new();
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for expr in exprs {
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if let ExprLit(ref lit) = expr.node {
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if let LitKind::Str(ref lit, _) = lit.node {
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result.push(&**lit);
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}
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}
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}
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return Some(result);
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}}
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None
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}
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/// Checks if the expressions matches
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/// ```rust
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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 Some(expr) = get_argument_fmtstr_parts(cx, expr) {
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expr.len() == 1 && expr[0].is_empty()
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} else {
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false
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}
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}
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/// Checks if the expressions matches
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/// ```rust
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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 ExprArray(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, _) = args[1].node,
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let Some(fun) = resolve_node(cx, args[1].id),
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match_def_path(cx, fun.def_id(), &paths::DISPLAY_FMT_METHOD),
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], {
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let ty = walk_ptrs_ty(cx.tcx.tables().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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