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Auto merge of #11136 - y21:enhance_read_line_without_trim, r=dswij

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[`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 ^^
This commit is contained in:
bors 2024-02-27 03:36:12 +00:00
commit fb060815b3
5 changed files with 140 additions and 38 deletions
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7
clippy_lints/src/methods/mod.rs
View File

@ -3420,11 +3420,12 @@
declare_clippy_lint! {
/// ### What it does
/// Looks for calls to [`Stdin::read_line`] to read a line from the standard input
/// into a string, then later attempting to parse this string into a type without first trimming it, which will
/// always fail because the string has a trailing newline in it.
/// into a string, then later attempting to use that string for an operation that will never
/// work for strings with a trailing newline character in it (e.g. parsing into a `i32`).
///
/// ### Why is this bad?
/// The `.parse()` call will always fail.
/// The operation will always fail at runtime no matter what the user enters, thus
/// making it a useless operation.
///
/// ### Example
/// ```rust,ignore

95
clippy_lints/src/methods/read_line_without_trim.rs
View File

@ -5,15 +5,26 @@
use clippy_utils::ty::is_type_diagnostic_item;
use clippy_utils::visitors::for_each_local_use_after_expr;
use clippy_utils::{get_parent_expr, match_def_path};
use rustc_ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::def::Res;
use rustc_hir::{Expr, ExprKind, QPath};
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty};
use rustc_span::sym;
use super::READ_LINE_WITHOUT_TRIM;
fn expr_is_string_literal_without_trailing_newline(expr: &Expr<'_>) -> bool {
if let ExprKind::Lit(lit) = expr.kind
&& let LitKind::Str(sym, _) = lit.node
{
!sym.as_str().ends_with('\n')
} else {
false
}
}
/// Will a `.parse::<ty>()` call fail if the input has a trailing newline?
fn parse_fails_on_trailing_newline(ty: Ty<'_>) -> bool {
// only allow a very limited set of types for now, for which we 100% know parsing will fail
@ -27,30 +38,66 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
&& let Res::Local(local_id) = path.res
{
// We've checked that `call` is a call to `Stdin::read_line()` with the right receiver,
// now let's check if the first use of the string passed to `::read_line()` is
// parsed into a type that will always fail if it has a trailing newline.
// now let's check if the first use of the string passed to `::read_line()`
// is used for operations that will always fail (e.g. parsing "6\n" into a number)
for_each_local_use_after_expr(cx, local_id, call.hir_id, |expr| {
if let Some(parent) = get_parent_expr(cx, expr)
&& let ExprKind::MethodCall(segment, .., span) = parent.kind
&& segment.ident.name == sym!(parse)
&& let parse_result_ty = cx.typeck_results().expr_ty(parent)
&& is_type_diagnostic_item(cx, parse_result_ty, sym::Result)
&& let ty::Adt(_, args) = parse_result_ty.kind()
&& let Some(ok_ty) = args[0].as_type()
&& parse_fails_on_trailing_newline(ok_ty)
{
let local_snippet = snippet(cx, expr.span, "<expr>");
span_lint_and_then(
cx,
READ_LINE_WITHOUT_TRIM,
span,
"calling `.parse()` without trimming the trailing newline character",
|diag| {
if let Some(parent) = get_parent_expr(cx, expr) {
let data = if let ExprKind::MethodCall(segment, recv, args, span) = parent.kind {
if segment.ident.name == sym!(parse)
&& let parse_result_ty = cx.typeck_results().expr_ty(parent)
&& is_type_diagnostic_item(cx, parse_result_ty, sym::Result)
&& let ty::Adt(_, substs) = parse_result_ty.kind()
&& let Some(ok_ty) = substs[0].as_type()
&& parse_fails_on_trailing_newline(ok_ty)
{
// Called `s.parse::<T>()` where `T` is a type we know for certain will fail
// if the input has a trailing newline
Some((
span,
"calling `.parse()` on a string without trimming the trailing newline character",
"checking",
))
} else if segment.ident.name == sym!(ends_with)
&& recv.span == expr.span
&& let [arg] = args
&& expr_is_string_literal_without_trailing_newline(arg)
{
// Called `s.ends_with(<some string literal>)` where the argument is a string literal that does
// not end with a newline, thus always evaluating to false
Some((
parent.span,
"checking the end of a string without trimming the trailing newline character",
"parsing",
))
} else {
None
}
} else if let ExprKind::Binary(binop, left, right) = parent.kind
&& let BinOpKind::Eq = binop.node
&& (expr_is_string_literal_without_trailing_newline(left)
|| expr_is_string_literal_without_trailing_newline(right))
{
// `s == <some string literal>` where the string literal does not end with a newline
Some((
parent.span,
"comparing a string literal without trimming the trailing newline character",
"comparison",
))
} else {
None
};
if let Some((primary_span, lint_message, operation)) = data {
span_lint_and_then(cx, READ_LINE_WITHOUT_TRIM, primary_span, lint_message, |diag| {
let local_snippet = snippet(cx, expr.span, "<expr>");
diag.span_note(
call.span,
"call to `.read_line()` here, \
which leaves a trailing newline character in the buffer, \
which in turn will cause `.parse()` to fail",
format!(
"call to `.read_line()` here, \
which leaves a trailing newline character in the buffer, \
which in turn will cause the {operation} to always fail"
),
);
diag.span_suggestion(
@ -59,8 +106,8 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
format!("{local_snippet}.trim_end()"),
Applicability::MachineApplicable,
);
},
);
});
}
}
// only consider the first use to prevent this scenario:

13
tests/ui/read_line_without_trim.fixed
View File

@ -31,4 +31,17 @@ fn main() {
std::io::stdin().read_line(&mut input).unwrap();
// this is actually ok, so don't lint here
let _x = input.parse::<String>().unwrap();
// comparing with string literals
let mut input = String::new();
std::io::stdin().read_line(&mut input).unwrap();
if input.trim_end() == "foo" {
println!("This will never ever execute!");
}
let mut input = String::new();
std::io::stdin().read_line(&mut input).unwrap();
if input.trim_end().ends_with("foo") {
println!("Neither will this");
}
}

13
tests/ui/read_line_without_trim.rs
View File

@ -31,4 +31,17 @@ fn main() {
std::io::stdin().read_line(&mut input).unwrap();
// this is actually ok, so don't lint here
let _x = input.parse::<String>().unwrap();
// comparing with string literals
let mut input = String::new();
std::io::stdin().read_line(&mut input).unwrap();
if input == "foo" {
println!("This will never ever execute!");
}
let mut input = String::new();
std::io::stdin().read_line(&mut input).unwrap();
if input.ends_with("foo") {
println!("Neither will this");
}
}

50
tests/ui/read_line_without_trim.stderr
View File

@ -1,4 +1,4 @@
error: calling `.parse()` without trimming the trailing newline character
error: calling `.parse()` on a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:12:25
|
LL | let _x: i32 = input.parse().unwrap();
@ -6,7 +6,7 @@ LL | let _x: i32 = input.parse().unwrap();
| |
| help: try: `input.trim_end()`
|
note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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
--> tests/ui/read_line_without_trim.rs:11:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
@ -14,7 +14,7 @@ LL | std::io::stdin().read_line(&mut input).unwrap();
= note: `-D clippy::read-line-without-trim` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::read_line_without_trim)]`
error: calling `.parse()` without trimming the trailing newline character
error: calling `.parse()` on a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:16:20
|
LL | let _x = input.parse::<i32>().unwrap();
@ -22,13 +22,13 @@ LL | let _x = input.parse::<i32>().unwrap();
| |
| help: try: `input.trim_end()`
|
note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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
--> tests/ui/read_line_without_trim.rs:15:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: calling `.parse()` without trimming the trailing newline character
error: calling `.parse()` on a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:20:20
|
LL | let _x = input.parse::<u32>().unwrap();
@ -36,13 +36,13 @@ LL | let _x = input.parse::<u32>().unwrap();
| |
| help: try: `input.trim_end()`
|
note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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
--> tests/ui/read_line_without_trim.rs:19:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: calling `.parse()` without trimming the trailing newline character
error: calling `.parse()` on a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:24:20
|
LL | let _x = input.parse::<f32>().unwrap();
@ -50,13 +50,13 @@ LL | let _x = input.parse::<f32>().unwrap();
| |
| help: try: `input.trim_end()`
|
note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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
--> tests/ui/read_line_without_trim.rs:23:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: calling `.parse()` without trimming the trailing newline character
error: calling `.parse()` on a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:28:20
|
LL | let _x = input.parse::<bool>().unwrap();
@ -64,11 +64,39 @@ LL | let _x = input.parse::<bool>().unwrap();
| |
| help: try: `input.trim_end()`
|
note: call to `.read_line()` here, which leaves a trailing newline character in the buffer, which in turn will cause `.parse()` to fail
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
--> tests/ui/read_line_without_trim.rs:27:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 5 previous errors
error: comparing a string literal without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:38:8
|
LL | if input == "foo" {
| -----^^^^^^^^^
| |
| help: try: `input.trim_end()`
|
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
--> tests/ui/read_line_without_trim.rs:37:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: checking the end of a string without trimming the trailing newline character
--> tests/ui/read_line_without_trim.rs:44:8
|
LL | if input.ends_with("foo") {
| -----^^^^^^^^^^^^^^^^^
| |
| help: try: `input.trim_end()`
|
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
--> tests/ui/read_line_without_trim.rs:43:5
|
LL | std::io::stdin().read_line(&mut input).unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 7 previous errors