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Auto merge of #11136 - y21:enhance_read_line_without_trim, r=dswij
[`read_line_without_trim`]: detect string literal comparison and `.ends_with()` calls
This lint now also realizes that a comparison like `s == "foo"` and calls such as `s.ends_with("foo")` will fail if `s` was initialized by a call to `Stdin::read_line` (because of the trailing newline).
changelog: [`read_line_without_trim`]: detect string literal comparison and `.ends_with()` calls
r? `@giraffate` assigning you because you reviewed #10970 that added this lint, so this is kinda a followup PR ^^
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fb060815b3
@ -3420,11 +3420,12 @@ declare_clippy_lint! {
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declare_clippy_lint! {
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/// ### What it does
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/// Looks for calls to [`Stdin::read_line`] to read a line from the standard input
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/// into a string, then later attempting to parse this string into a type without first trimming it, which will
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/// always fail because the string has a trailing newline in it.
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/// into a string, then later attempting to use that string for an operation that will never
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/// work for strings with a trailing newline character in it (e.g. parsing into a `i32`).
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///
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/// ### Why is this bad?
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/// The `.parse()` call will always fail.
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/// The operation will always fail at runtime no matter what the user enters, thus
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/// making it a useless operation.
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///
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/// ### Example
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/// ```rust,ignore
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@ -5,15 +5,26 @@ use clippy_utils::source::snippet;
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use clippy_utils::ty::is_type_diagnostic_item;
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use clippy_utils::visitors::for_each_local_use_after_expr;
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use clippy_utils::{get_parent_expr, match_def_path};
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use rustc_ast::LitKind;
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::{Expr, ExprKind, QPath};
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use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
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use rustc_lint::LateContext;
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use rustc_middle::ty::{self, Ty};
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use rustc_span::sym;
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use super::READ_LINE_WITHOUT_TRIM;
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fn expr_is_string_literal_without_trailing_newline(expr: &Expr<'_>) -> bool {
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if let ExprKind::Lit(lit) = expr.kind
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&& let LitKind::Str(sym, _) = lit.node
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{
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!sym.as_str().ends_with('\n')
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} else {
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false
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}
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}
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/// Will a `.parse::<ty>()` call fail if the input has a trailing newline?
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fn parse_fails_on_trailing_newline(ty: Ty<'_>) -> bool {
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// only allow a very limited set of types for now, for which we 100% know parsing will fail
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@ -27,30 +38,66 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
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&& let Res::Local(local_id) = path.res
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{
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// We've checked that `call` is a call to `Stdin::read_line()` with the right receiver,
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// now let's check if the first use of the string passed to `::read_line()` is
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// parsed into a type that will always fail if it has a trailing newline.
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// now let's check if the first use of the string passed to `::read_line()`
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// is used for operations that will always fail (e.g. parsing "6\n" into a number)
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for_each_local_use_after_expr(cx, local_id, call.hir_id, |expr| {
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if let Some(parent) = get_parent_expr(cx, expr)
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&& let ExprKind::MethodCall(segment, .., span) = parent.kind
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&& segment.ident.name == sym!(parse)
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&& let parse_result_ty = cx.typeck_results().expr_ty(parent)
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&& is_type_diagnostic_item(cx, parse_result_ty, sym::Result)
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&& let ty::Adt(_, args) = parse_result_ty.kind()
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&& let Some(ok_ty) = args[0].as_type()
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&& parse_fails_on_trailing_newline(ok_ty)
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{
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let local_snippet = snippet(cx, expr.span, "<expr>");
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span_lint_and_then(
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cx,
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READ_LINE_WITHOUT_TRIM,
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span,
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"calling `.parse()` without trimming the trailing newline character",
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|diag| {
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if let Some(parent) = get_parent_expr(cx, expr) {
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let data = if let ExprKind::MethodCall(segment, recv, args, span) = parent.kind {
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if segment.ident.name == sym!(parse)
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&& let parse_result_ty = cx.typeck_results().expr_ty(parent)
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&& is_type_diagnostic_item(cx, parse_result_ty, sym::Result)
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&& let ty::Adt(_, substs) = parse_result_ty.kind()
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&& let Some(ok_ty) = substs[0].as_type()
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&& parse_fails_on_trailing_newline(ok_ty)
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{
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// Called `s.parse::<T>()` where `T` is a type we know for certain will fail
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// if the input has a trailing newline
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Some((
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span,
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"calling `.parse()` on a string without trimming the trailing newline character",
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"checking",
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))
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} else if segment.ident.name == sym!(ends_with)
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&& recv.span == expr.span
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&& let [arg] = args
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&& expr_is_string_literal_without_trailing_newline(arg)
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{
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// Called `s.ends_with(<some string literal>)` where the argument is a string literal that does
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// not end with a newline, thus always evaluating to false
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Some((
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parent.span,
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"checking the end of a string without trimming the trailing newline character",
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"parsing",
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))
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} else {
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None
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}
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} else if let ExprKind::Binary(binop, left, right) = parent.kind
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&& let BinOpKind::Eq = binop.node
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&& (expr_is_string_literal_without_trailing_newline(left)
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|| expr_is_string_literal_without_trailing_newline(right))
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{
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// `s == <some string literal>` where the string literal does not end with a newline
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Some((
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parent.span,
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"comparing a string literal without trimming the trailing newline character",
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"comparison",
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))
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} else {
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None
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};
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if let Some((primary_span, lint_message, operation)) = data {
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span_lint_and_then(cx, READ_LINE_WITHOUT_TRIM, primary_span, lint_message, |diag| {
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let local_snippet = snippet(cx, expr.span, "<expr>");
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diag.span_note(
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call.span,
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"call to `.read_line()` here, \
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which leaves a trailing newline character in the buffer, \
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which in turn will cause `.parse()` to fail",
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format!(
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"call to `.read_line()` here, \
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which leaves a trailing newline character in the buffer, \
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which in turn will cause the {operation} to always fail"
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),
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);
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diag.span_suggestion(
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@ -59,8 +106,8 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
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format!("{local_snippet}.trim_end()"),
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Applicability::MachineApplicable,
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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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// only consider the first use to prevent this scenario:
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@ -31,4 +31,17 @@ fn main() {
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std::io::stdin().read_line(&mut input).unwrap();
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// this is actually ok, so don't lint here
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let _x = input.parse::<String>().unwrap();
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// comparing with string literals
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let mut input = String::new();
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std::io::stdin().read_line(&mut input).unwrap();
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if input.trim_end() == "foo" {
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println!("This will never ever execute!");
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}
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let mut input = String::new();
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std::io::stdin().read_line(&mut input).unwrap();
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if input.trim_end().ends_with("foo") {
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println!("Neither will this");
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}
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}
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@ -31,4 +31,17 @@ fn main() {
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std::io::stdin().read_line(&mut input).unwrap();
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// this is actually ok, so don't lint here
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let _x = input.parse::<String>().unwrap();
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// comparing with string literals
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let mut input = String::new();
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std::io::stdin().read_line(&mut input).unwrap();
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if input == "foo" {
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println!("This will never ever execute!");
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}
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let mut input = String::new();
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std::io::stdin().read_line(&mut input).unwrap();
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if input.ends_with("foo") {
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println!("Neither will this");
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}
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}
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@ -1,4 +1,4 @@
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error: calling `.parse()` without trimming the trailing newline character
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error: calling `.parse()` on a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:12:25
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LL | let _x: i32 = input.parse().unwrap();
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@ -6,7 +6,7 @@ LL | let _x: i32 = input.parse().unwrap();
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| |
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| help: try: `input.trim_end()`
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the checking to always fail
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--> tests/ui/read_line_without_trim.rs:11:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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@ -14,7 +14,7 @@ LL | std::io::stdin().read_line(&mut input).unwrap();
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= note: `-D clippy::read-line-without-trim` implied by `-D warnings`
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= help: to override `-D warnings` add `#[allow(clippy::read_line_without_trim)]`
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error: calling `.parse()` without trimming the trailing newline character
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error: calling `.parse()` on a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:16:20
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LL | let _x = input.parse::<i32>().unwrap();
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@ -22,13 +22,13 @@ LL | let _x = input.parse::<i32>().unwrap();
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| |
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| help: try: `input.trim_end()`
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the checking to always fail
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--> tests/ui/read_line_without_trim.rs:15:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: calling `.parse()` without trimming the trailing newline character
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error: calling `.parse()` on a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:20:20
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LL | let _x = input.parse::<u32>().unwrap();
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@ -36,13 +36,13 @@ LL | let _x = input.parse::<u32>().unwrap();
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| |
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| help: try: `input.trim_end()`
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|
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the checking to always fail
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--> tests/ui/read_line_without_trim.rs:19:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: calling `.parse()` without trimming the trailing newline character
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error: calling `.parse()` on a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:24:20
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LL | let _x = input.parse::<f32>().unwrap();
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@ -50,13 +50,13 @@ LL | let _x = input.parse::<f32>().unwrap();
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| |
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| help: try: `input.trim_end()`
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|
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the checking to always fail
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--> tests/ui/read_line_without_trim.rs:23:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: calling `.parse()` without trimming the trailing newline character
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error: calling `.parse()` on a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:28:20
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LL | let _x = input.parse::<bool>().unwrap();
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@ -64,11 +64,39 @@ LL | let _x = input.parse::<bool>().unwrap();
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| |
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| help: try: `input.trim_end()`
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|
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the checking to always fail
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--> tests/ui/read_line_without_trim.rs:27:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 5 previous errors
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error: comparing a string literal without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:38:8
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LL | if input == "foo" {
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| -----^^^^^^^^^
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| |
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| help: try: `input.trim_end()`
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|
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the comparison to always fail
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--> tests/ui/read_line_without_trim.rs:37:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: checking the end of a string without trimming the trailing newline character
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--> tests/ui/read_line_without_trim.rs:44:8
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LL | if input.ends_with("foo") {
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| -----^^^^^^^^^^^^^^^^^
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| |
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| help: try: `input.trim_end()`
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|
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note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause the parsing to always fail
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--> tests/ui/read_line_without_trim.rs:43:5
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LL | std::io::stdin().read_line(&mut input).unwrap();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 7 previous errors
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