| use crate::utils::paths; |
| use crate::utils::{ |
| is_expn_of, is_type_diagnostic_item, last_path_segment, match_def_path, match_function_call, snippet, |
| span_lint_and_then, walk_ptrs_ty, |
| }; |
| use if_chain::if_chain; |
| use rustc_ast::ast::LitKind; |
| use rustc_errors::Applicability; |
| use rustc_hir::{Arm, BorrowKind, Expr, ExprKind, MatchSource, PatKind}; |
| use rustc_lint::{LateContext, LateLintPass, LintContext}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::source_map::Span; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for the use of `format!("string literal with no |
| /// argument")` and `format!("{}", foo)` where `foo` is a string. |
| /// |
| /// **Why is this bad?** There is no point of doing that. `format!("foo")` can |
| /// be replaced by `"foo".to_owned()` if you really need a `String`. The even |
| /// worse `&format!("foo")` is often encountered in the wild. `format!("{}", |
| /// foo)` can be replaced by `foo.clone()` if `foo: String` or `foo.to_owned()` |
| /// if `foo: &str`. |
| /// |
| /// **Known problems:** None. |
| /// |
| /// **Examples:** |
| /// ```rust |
| /// |
| /// // Bad |
| /// # let foo = "foo"; |
| /// format!("{}", foo); |
| /// |
| /// // Good |
| /// format!("foo"); |
| /// ``` |
| pub USELESS_FORMAT, |
| complexity, |
| "useless use of `format!`" |
| } |
| |
| declare_lint_pass!(UselessFormat => [USELESS_FORMAT]); |
| |
| impl<'tcx> LateLintPass<'tcx> for UselessFormat { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| let span = match is_expn_of(expr.span, "format") { |
| Some(s) if !s.from_expansion() => s, |
| _ => return, |
| }; |
| |
| // Operate on the only argument of `alloc::fmt::format`. |
| if let Some(sugg) = on_new_v1(cx, expr) { |
| span_useless_format(cx, span, "consider using `.to_string()`", sugg); |
| } else if let Some(sugg) = on_new_v1_fmt(cx, expr) { |
| span_useless_format(cx, span, "consider using `.to_string()`", sugg); |
| } |
| } |
| } |
| |
| fn span_useless_format<T: LintContext>(cx: &T, span: Span, help: &str, mut sugg: String) { |
| let to_replace = span.source_callsite(); |
| |
| // The callsite span contains the statement semicolon for some reason. |
| let snippet = snippet(cx, to_replace, ".."); |
| if snippet.ends_with(';') { |
| sugg.push(';'); |
| } |
| |
| span_lint_and_then(cx, USELESS_FORMAT, span, "useless use of `format!`", |diag| { |
| diag.span_suggestion( |
| to_replace, |
| help, |
| sugg, |
| Applicability::MachineApplicable, // snippet |
| ); |
| }); |
| } |
| |
| fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) -> Option<String> { |
| if_chain! { |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref format_args) = expr.kind; |
| if let ExprKind::Array(ref elems) = arms[0].body.kind; |
| if elems.len() == 1; |
| if let Some(args) = match_function_call(cx, &elems[0], &paths::FMT_ARGUMENTV1_NEW); |
| // matches `core::fmt::Display::fmt` |
| if args.len() == 2; |
| if let ExprKind::Path(ref qpath) = args[1].kind; |
| if let Some(did) = cx.qpath_res(qpath, args[1].hir_id).opt_def_id(); |
| if match_def_path(cx, did, &paths::DISPLAY_FMT_METHOD); |
| // check `(arg0,)` in match block |
| if let PatKind::Tuple(ref pats, None) = arms[0].pat.kind; |
| if pats.len() == 1; |
| then { |
| let ty = walk_ptrs_ty(cx.tables().pat_ty(&pats[0])); |
| if ty.kind != rustc_middle::ty::Str && !is_type_diagnostic_item(cx, ty, sym!(string_type)) { |
| return None; |
| } |
| if let ExprKind::Lit(ref lit) = format_args.kind { |
| if let LitKind::Str(ref s, _) = lit.node { |
| return Some(format!("{:?}.to_string()", s.as_str())); |
| } |
| } else { |
| let snip = snippet(cx, format_args.span, "<arg>"); |
| if let ExprKind::MethodCall(ref path, _, _, _) = format_args.kind { |
| if path.ident.name == sym!(to_string) { |
| return Some(format!("{}", snip)); |
| } |
| } else if let ExprKind::Binary(..) = format_args.kind { |
| return Some(format!("{}", snip)); |
| } |
| return Some(format!("{}.to_string()", snip)); |
| } |
| } |
| } |
| None |
| } |
| |
| fn on_new_v1<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> { |
| if_chain! { |
| if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1); |
| if args.len() == 2; |
| // Argument 1 in `new_v1()` |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind; |
| if let ExprKind::Array(ref pieces) = arr.kind; |
| if pieces.len() == 1; |
| if let ExprKind::Lit(ref lit) = pieces[0].kind; |
| if let LitKind::Str(ref s, _) = lit.node; |
| // Argument 2 in `new_v1()` |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind; |
| if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind; |
| if arms.len() == 1; |
| if let ExprKind::Tup(ref tup) = matchee.kind; |
| then { |
| // `format!("foo")` expansion contains `match () { () => [], }` |
| if tup.is_empty() { |
| return Some(format!("{:?}.to_string()", s.as_str())); |
| } else if s.as_str().is_empty() { |
| return on_argumentv1_new(cx, &tup[0], arms); |
| } |
| } |
| } |
| None |
| } |
| |
| fn on_new_v1_fmt<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<String> { |
| if_chain! { |
| if let Some(args) = match_function_call(cx, expr, &paths::FMT_ARGUMENTS_NEW_V1_FORMATTED); |
| if args.len() == 3; |
| if check_unformatted(&args[2]); |
| // Argument 1 in `new_v1_formatted()` |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arr) = args[0].kind; |
| if let ExprKind::Array(ref pieces) = arr.kind; |
| if pieces.len() == 1; |
| if let ExprKind::Lit(ref lit) = pieces[0].kind; |
| if let LitKind::Str(..) = lit.node; |
| // Argument 2 in `new_v1_formatted()` |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg1) = args[1].kind; |
| if let ExprKind::Match(ref matchee, ref arms, MatchSource::Normal) = arg1.kind; |
| if arms.len() == 1; |
| if let ExprKind::Tup(ref tup) = matchee.kind; |
| then { |
| return on_argumentv1_new(cx, &tup[0], arms); |
| } |
| } |
| None |
| } |
| |
| /// Checks if the expression matches |
| /// ```rust,ignore |
| /// &[_ { |
| /// format: _ { |
| /// width: _::Implied, |
| /// precision: _::Implied, |
| /// ... |
| /// }, |
| /// ..., |
| /// }] |
| /// ``` |
| fn check_unformatted(expr: &Expr<'_>) -> bool { |
| if_chain! { |
| if let ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) = expr.kind; |
| if let ExprKind::Array(ref exprs) = expr.kind; |
| if exprs.len() == 1; |
| // struct `core::fmt::rt::v1::Argument` |
| if let ExprKind::Struct(_, ref fields, _) = exprs[0].kind; |
| if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym!(format)); |
| // struct `core::fmt::rt::v1::FormatSpec` |
| if let ExprKind::Struct(_, ref fields, _) = format_field.expr.kind; |
| if let Some(precision_field) = fields.iter().find(|f| f.ident.name == sym!(precision)); |
| if let ExprKind::Path(ref precision_path) = precision_field.expr.kind; |
| if last_path_segment(precision_path).ident.name == sym!(Implied); |
| if let Some(width_field) = fields.iter().find(|f| f.ident.name == sym!(width)); |
| if let ExprKind::Path(ref width_qpath) = width_field.expr.kind; |
| if last_path_segment(width_qpath).ident.name == sym!(Implied); |
| then { |
| return true; |
| } |
| } |
| |
| false |
| } |
