1 use clippy_utils::diagnostics::{span_lint, span_lint_and_help, span_lint_and_sugg};
2 use clippy_utils::source::{snippet, snippet_with_applicability};
3 use clippy_utils::ty::is_type_lang_item;
4 use clippy_utils::{get_parent_expr, is_lint_allowed, match_function_call, method_calls, paths};
5 use clippy_utils::{peel_blocks, SpanlessEq};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::def_id::DefId;
9 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, LangItem, QPath};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::lint::in_external_macro;
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 use rustc_span::source_map::Spanned;
17 declare_clippy_lint! {
19 /// Checks for string appends of the form `x = x + y` (without
22 /// ### Why is this bad?
23 /// It's not really bad, but some people think that the
24 /// `.push_str(_)` method is more readable.
28 /// let mut x = "Hello".to_owned();
29 /// x = x + ", World";
33 /// x.push_str(", World");
35 #[clippy::version = "pre 1.29.0"]
36 pub STRING_ADD_ASSIGN,
38 "using `x = x + ..` where x is a `String` instead of `push_str()`"
41 declare_clippy_lint! {
43 /// Checks for all instances of `x + _` where `x` is of type
44 /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
47 /// ### Why is this bad?
48 /// It's not bad in and of itself. However, this particular
49 /// `Add` implementation is asymmetric (the other operand need not be `String`,
50 /// but `x` does), while addition as mathematically defined is symmetric, also
51 /// the `String::push_str(_)` function is a perfectly good replacement.
52 /// Therefore, some dislike it and wish not to have it in their code.
54 /// That said, other people think that string addition, having a long tradition
55 /// in other languages is actually fine, which is why we decided to make this
56 /// particular lint `allow` by default.
60 /// let x = "Hello".to_owned();
66 /// let mut x = "Hello".to_owned();
67 /// x.push_str(", World");
69 #[clippy::version = "pre 1.29.0"]
72 "using `x + ..` where x is a `String` instead of `push_str()`"
75 declare_clippy_lint! {
77 /// Checks for the `as_bytes` method called on string literals
78 /// that contain only ASCII characters.
80 /// ### Why is this bad?
81 /// Byte string literals (e.g., `b"foo"`) can be used
82 /// instead. They are shorter but less discoverable than `as_bytes()`.
84 /// ### Known problems
85 /// `"str".as_bytes()` and the suggested replacement of `b"str"` are not
86 /// equivalent because they have different types. The former is `&[u8]`
87 /// while the latter is `&[u8; 3]`. That means in general they will have a
88 /// different set of methods and different trait implementations.
91 /// fn f(v: Vec<u8>) {}
93 /// f("...".as_bytes().to_owned()); // works
94 /// f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>
96 /// fn g(r: impl std::io::Read) {}
98 /// g("...".as_bytes()); // works
99 /// g(b"..."); // does not work
102 /// The actual equivalent of `"str".as_bytes()` with the same type is not
103 /// `b"str"` but `&b"str"[..]`, which is a great deal of punctuation and not
104 /// more readable than a function call.
108 /// let bstr = "a byte string".as_bytes();
113 /// let bstr = b"a byte string";
115 #[clippy::version = "pre 1.29.0"]
116 pub STRING_LIT_AS_BYTES,
118 "calling `as_bytes` on a string literal instead of using a byte string literal"
121 declare_clippy_lint! {
123 /// Checks for slice operations on strings
125 /// ### Why is this bad?
126 /// UTF-8 characters span multiple bytes, and it is easy to inadvertently confuse character
127 /// counts and string indices. This may lead to panics, and should warrant some test cases
128 /// containing wide UTF-8 characters. This lint is most useful in code that should avoid
129 /// panics at all costs.
131 /// ### Known problems
132 /// Probably lots of false positives. If an index comes from a known valid position (e.g.
133 /// obtained via `char_indices` over the same string), it is totally OK.
136 /// ```rust,should_panic
137 /// &"Ölkanne"[1..];
139 #[clippy::version = "1.58.0"]
145 declare_lint_pass!(StringAdd => [STRING_ADD, STRING_ADD_ASSIGN, STRING_SLICE]);
147 impl<'tcx> LateLintPass<'tcx> for StringAdd {
148 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
149 if in_external_macro(cx.sess(), e.span) {
155 node: BinOpKind::Add, ..
160 if is_string(cx, left) {
161 if !is_lint_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
162 let parent = get_parent_expr(cx, e);
163 if let Some(p) = parent {
164 if let ExprKind::Assign(target, _, _) = p.kind {
165 // avoid duplicate matches
166 if SpanlessEq::new(cx).eq_expr(target, left) {
176 "you added something to a string. Consider using `String::push_str()` instead",
180 ExprKind::Assign(target, src, _) => {
181 if is_string(cx, target) && is_add(cx, src, target) {
186 "you assigned the result of adding something to this string. Consider using \
187 `String::push_str()` instead",
191 ExprKind::Index(target, _idx) => {
192 let e_ty = cx.typeck_results().expr_ty(target).peel_refs();
193 if matches!(e_ty.kind(), ty::Str) || is_type_lang_item(cx, e_ty, LangItem::String) {
198 "indexing into a string may panic if the index is within a UTF-8 character",
207 fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
208 is_type_lang_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), LangItem::String)
211 fn is_add(cx: &LateContext<'_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {
212 match peel_blocks(src).kind {
215 node: BinOpKind::Add, ..
219 ) => SpanlessEq::new(cx).eq_expr(target, left),
224 declare_clippy_lint! {
226 /// Check if the string is transformed to byte array and casted back to string.
228 /// ### Why is this bad?
229 /// It's unnecessary, the string can be used directly.
233 /// std::str::from_utf8(&"Hello World!".as_bytes()[6..11]).unwrap();
238 /// &"Hello World!"[6..11];
240 #[clippy::version = "1.50.0"]
241 pub STRING_FROM_UTF8_AS_BYTES,
243 "casting string slices to byte slices and back"
246 // Max length a b"foo" string can take
247 const MAX_LENGTH_BYTE_STRING_LIT: usize = 32;
249 declare_lint_pass!(StringLitAsBytes => [STRING_LIT_AS_BYTES, STRING_FROM_UTF8_AS_BYTES]);
251 impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
252 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
253 use rustc_ast::LitKind;
256 // Find std::str::converts::from_utf8
257 if let Some(args) = match_function_call(cx, e, &paths::STR_FROM_UTF8);
259 // Find string::as_bytes
260 if let ExprKind::AddrOf(BorrowKind::Ref, _, args) = args[0].kind;
261 if let ExprKind::Index(left, right) = args.kind;
262 let (method_names, expressions, _) = method_calls(left, 1);
263 if method_names.len() == 1;
264 if expressions.len() == 1;
265 if expressions[0].1.is_empty();
266 if method_names[0] == sym!(as_bytes);
269 if let ExprKind::Struct(QPath::LangItem(LangItem::Range, ..), _, _) = right.kind;
272 let mut applicability = Applicability::MachineApplicable;
273 let string_expression = &expressions[0].0;
275 let snippet_app = snippet_with_applicability(
277 string_expression.span, "..",
283 STRING_FROM_UTF8_AS_BYTES,
285 "calling a slice of `as_bytes()` with `from_utf8` should be not necessary",
287 format!("Some(&{snippet_app}[{}])", snippet(cx, right.span, "..")),
294 if let ExprKind::MethodCall(path, receiver, ..) = &e.kind;
295 if path.ident.name == sym!(as_bytes);
296 if let ExprKind::Lit(lit) = &receiver.kind;
297 if let LitKind::Str(lit_content, _) = &lit.node;
299 let callsite = snippet(cx, receiver.span.source_callsite(), r#""foo""#);
300 let mut applicability = Applicability::MachineApplicable;
301 if callsite.starts_with("include_str!") {
306 "calling `as_bytes()` on `include_str!(..)`",
307 "consider using `include_bytes!(..)` instead",
308 snippet_with_applicability(cx, receiver.span, r#""foo""#, &mut applicability).replacen(
315 } else if lit_content.as_str().is_ascii()
316 && lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
317 && !receiver.span.from_expansion()
323 "calling `as_bytes()` on a string literal",
324 "consider using a byte string literal instead",
327 snippet_with_applicability(cx, receiver.span, r#""foo""#, &mut applicability)
336 if let ExprKind::MethodCall(path, recv, [], _) = &e.kind;
337 if path.ident.name == sym!(into_bytes);
338 if let ExprKind::MethodCall(path, recv, [], _) = &recv.kind;
339 if matches!(path.ident.name.as_str(), "to_owned" | "to_string");
340 if let ExprKind::Lit(lit) = &recv.kind;
341 if let LitKind::Str(lit_content, _) = &lit.node;
343 if lit_content.as_str().is_ascii();
344 if lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT;
345 if !recv.span.from_expansion();
347 let mut applicability = Applicability::MachineApplicable;
353 "calling `into_bytes()` on a string literal",
354 "consider using a byte string literal instead",
357 snippet_with_applicability(cx, recv.span, r#""..""#, &mut applicability)
366 declare_clippy_lint! {
368 /// This lint checks for `.to_string()` method calls on values of type `&str`.
370 /// ### Why is this bad?
371 /// The `to_string` method is also used on other types to convert them to a string.
372 /// When called on a `&str` it turns the `&str` into the owned variant `String`, which can be better
373 /// expressed with `.to_owned()`.
377 /// // example code where clippy issues a warning
378 /// let _ = "str".to_string();
382 /// // example code which does not raise clippy warning
383 /// let _ = "str".to_owned();
385 #[clippy::version = "pre 1.29.0"]
388 "using `to_string()` on a `&str`, which should be `to_owned()`"
391 declare_lint_pass!(StrToString => [STR_TO_STRING]);
393 impl<'tcx> LateLintPass<'tcx> for StrToString {
394 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
396 if let ExprKind::MethodCall(path, self_arg, ..) = &expr.kind;
397 if path.ident.name == sym::to_string;
398 let ty = cx.typeck_results().expr_ty(self_arg);
399 if let ty::Ref(_, ty, ..) = ty.kind();
400 if *ty.kind() == ty::Str;
406 "`to_string()` called on a `&str`",
408 "consider using `.to_owned()`",
415 declare_clippy_lint! {
417 /// This lint checks for `.to_string()` method calls on values of type `String`.
419 /// ### Why is this bad?
420 /// The `to_string` method is also used on other types to convert them to a string.
421 /// When called on a `String` it only clones the `String`, which can be better expressed with `.clone()`.
425 /// // example code where clippy issues a warning
426 /// let msg = String::from("Hello World");
427 /// let _ = msg.to_string();
431 /// // example code which does not raise clippy warning
432 /// let msg = String::from("Hello World");
433 /// let _ = msg.clone();
435 #[clippy::version = "pre 1.29.0"]
436 pub STRING_TO_STRING,
438 "using `to_string()` on a `String`, which should be `clone()`"
441 declare_lint_pass!(StringToString => [STRING_TO_STRING]);
443 impl<'tcx> LateLintPass<'tcx> for StringToString {
444 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
446 if let ExprKind::MethodCall(path, self_arg, ..) = &expr.kind;
447 if path.ident.name == sym::to_string;
448 let ty = cx.typeck_results().expr_ty(self_arg);
449 if is_type_lang_item(cx, ty, LangItem::String);
455 "`to_string()` called on a `String`",
457 "consider using `.clone()`",
464 declare_clippy_lint! {
466 /// Warns about calling `str::trim` (or variants) before `str::split_whitespace`.
468 /// ### Why is this bad?
469 /// `split_whitespace` already ignores leading and trailing whitespace.
473 /// " A B C ".trim().split_whitespace();
477 /// " A B C ".split_whitespace();
479 #[clippy::version = "1.62.0"]
480 pub TRIM_SPLIT_WHITESPACE,
482 "using `str::trim()` or alike before `str::split_whitespace`"
484 declare_lint_pass!(TrimSplitWhitespace => [TRIM_SPLIT_WHITESPACE]);
486 impl<'tcx> LateLintPass<'tcx> for TrimSplitWhitespace {
487 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
488 let tyckres = cx.typeck_results();
490 if let ExprKind::MethodCall(path, split_recv, [], split_ws_span) = expr.kind;
491 if path.ident.name == sym!(split_whitespace);
492 if let Some(split_ws_def_id) = tyckres.type_dependent_def_id(expr.hir_id);
493 if cx.tcx.is_diagnostic_item(sym::str_split_whitespace, split_ws_def_id);
494 if let ExprKind::MethodCall(path, _trim_recv, [], trim_span) = split_recv.kind;
495 if let trim_fn_name @ ("trim" | "trim_start" | "trim_end") = path.ident.name.as_str();
496 if let Some(trim_def_id) = tyckres.type_dependent_def_id(split_recv.hir_id);
497 if is_one_of_trim_diagnostic_items(cx, trim_def_id);
501 TRIM_SPLIT_WHITESPACE,
502 trim_span.with_hi(split_ws_span.lo()),
503 &format!("found call to `str::{trim_fn_name}` before `str::split_whitespace`"),
504 &format!("remove `{trim_fn_name}()`"),
506 Applicability::MachineApplicable,
513 fn is_one_of_trim_diagnostic_items(cx: &LateContext<'_>, trim_def_id: DefId) -> bool {
514 cx.tcx.is_diagnostic_item(sym::str_trim, trim_def_id)
515 || cx.tcx.is_diagnostic_item(sym::str_trim_start, trim_def_id)
516 || cx.tcx.is_diagnostic_item(sym::str_trim_end, trim_def_id)