| use clippy_utils::diagnostics::span_lint_and_sugg; |
| use rustc_ast::LitKind; |
| use rustc_errors::Applicability::MachineApplicable; |
| use rustc_hir::{Expr, ExprKind, PathSegment, QPath, TyKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_middle::ty; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use rustc_span::{sym, symbol, Span}; |
| |
| declare_clippy_lint! { |
| /// ### What it does |
| /// |
| /// Checks for usage of `""` to create a `String`, such as `"".to_string()`, `"".to_owned()`, |
| /// `String::from("")` and others. |
| /// |
| /// ### Why is this bad? |
| /// |
| /// Different ways of creating an empty string makes your code less standardized, which can |
| /// be confusing. |
| /// |
| /// ### Example |
| /// ```no_run |
| /// let a = "".to_string(); |
| /// let b: String = "".into(); |
| /// ``` |
| /// Use instead: |
| /// ```no_run |
| /// let a = String::new(); |
| /// let b = String::new(); |
| /// ``` |
| #[clippy::version = "1.65.0"] |
| pub MANUAL_STRING_NEW, |
| pedantic, |
| "empty String is being created manually" |
| } |
| declare_lint_pass!(ManualStringNew => [MANUAL_STRING_NEW]); |
| |
| impl LateLintPass<'_> for ManualStringNew { |
| fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) { |
| if expr.span.from_expansion() { |
| return; |
| } |
| |
| let ty = cx.typeck_results().expr_ty(expr); |
| match ty.kind() { |
| ty::Adt(adt_def, _) if adt_def.is_struct() => { |
| if cx.tcx.lang_items().string() != Some(adt_def.did()) { |
| return; |
| } |
| }, |
| _ => return, |
| } |
| |
| match expr.kind { |
| ExprKind::Call(func, args) => { |
| parse_call(cx, expr.span, func, args); |
| }, |
| ExprKind::MethodCall(path_segment, receiver, ..) => { |
| parse_method_call(cx, expr.span, path_segment, receiver); |
| }, |
| _ => (), |
| } |
| } |
| } |
| |
| /// Checks if an expression's kind corresponds to an empty &str. |
| fn is_expr_kind_empty_str(expr_kind: &ExprKind<'_>) -> bool { |
| if let ExprKind::Lit(lit) = expr_kind |
| && let LitKind::Str(value, _) = lit.node |
| && value == symbol::kw::Empty |
| { |
| return true; |
| } |
| |
| false |
| } |
| |
| fn warn_then_suggest(cx: &LateContext<'_>, span: Span) { |
| span_lint_and_sugg( |
| cx, |
| MANUAL_STRING_NEW, |
| span, |
| "empty String is being created manually", |
| "consider using", |
| "String::new()".into(), |
| MachineApplicable, |
| ); |
| } |
| |
| /// Tries to parse an expression as a method call, emitting the warning if necessary. |
| fn parse_method_call(cx: &LateContext<'_>, span: Span, path_segment: &PathSegment<'_>, receiver: &Expr<'_>) { |
| let ident = path_segment.ident.as_str(); |
| let method_arg_kind = &receiver.kind; |
| if ["to_string", "to_owned", "into"].contains(&ident) && is_expr_kind_empty_str(method_arg_kind) { |
| warn_then_suggest(cx, span); |
| } else if let ExprKind::Call(func, args) = method_arg_kind { |
| // If our first argument is a function call itself, it could be an `unwrap`-like function. |
| // E.g. String::try_from("hello").unwrap(), TryFrom::try_from("").expect("hello"), etc. |
| parse_call(cx, span, func, args); |
| } |
| } |
| |
| /// Tries to parse an expression as a function call, emitting the warning if necessary. |
| fn parse_call(cx: &LateContext<'_>, span: Span, func: &Expr<'_>, args: &[Expr<'_>]) { |
| if args.len() != 1 { |
| return; |
| } |
| |
| let arg_kind = &args[0].kind; |
| if let ExprKind::Path(qpath) = &func.kind { |
| if let QPath::TypeRelative(_, _) = qpath { |
| // String::from(...) or String::try_from(...) |
| if let QPath::TypeRelative(ty, path_seg) = qpath |
| && [sym::from, sym::try_from].contains(&path_seg.ident.name) |
| && let TyKind::Path(qpath) = &ty.kind |
| && let QPath::Resolved(_, path) = qpath |
| && let [path_seg] = path.segments |
| && path_seg.ident.name == sym::String |
| && is_expr_kind_empty_str(arg_kind) |
| { |
| warn_then_suggest(cx, span); |
| } |
| } else if let QPath::Resolved(_, path) = qpath { |
| // From::from(...) or TryFrom::try_from(...) |
| if let [path_seg1, path_seg2] = path.segments |
| && is_expr_kind_empty_str(arg_kind) |
| && ((path_seg1.ident.name == sym::From && path_seg2.ident.name == sym::from) |
| || (path_seg1.ident.name == sym::TryFrom && path_seg2.ident.name == sym::try_from)) |
| { |
| warn_then_suggest(cx, span); |
| } |
| } |
| } |
| } |