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_diagnostic_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::{BinOpKind, BorrowKind, Expr, ExprKind, LangItem, QPath};
9 use rustc_lint::{LateContext, LateLintPass, LintContext};
10 use rustc_middle::lint::in_external_macro;
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Spanned;
16 declare_clippy_lint! {
18 /// Checks for string appends of the form `x = x + y` (without
21 /// ### Why is this bad?
22 /// It's not really bad, but some people think that the
23 /// `.push_str(_)` method is more readable.
27 /// let mut x = "Hello".to_owned();
28 /// x = x + ", World";
32 /// x.push_str(", World");
34 #[clippy::version = "pre 1.29.0"]
35 pub STRING_ADD_ASSIGN,
37 "using `x = x + ..` where x is a `String` instead of `push_str()`"
40 declare_clippy_lint! {
42 /// Checks for all instances of `x + _` where `x` is of type
43 /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
46 /// ### Why is this bad?
47 /// It's not bad in and of itself. However, this particular
48 /// `Add` implementation is asymmetric (the other operand need not be `String`,
49 /// but `x` does), while addition as mathematically defined is symmetric, also
50 /// the `String::push_str(_)` function is a perfectly good replacement.
51 /// Therefore, some dislike it and wish not to have it in their code.
53 /// That said, other people think that string addition, having a long tradition
54 /// in other languages is actually fine, which is why we decided to make this
55 /// particular lint `allow` by default.
59 /// let x = "Hello".to_owned();
62 #[clippy::version = "pre 1.29.0"]
65 "using `x + ..` where x is a `String` instead of `push_str()`"
68 declare_clippy_lint! {
70 /// Checks for the `as_bytes` method called on string literals
71 /// that contain only ASCII characters.
73 /// ### Why is this bad?
74 /// Byte string literals (e.g., `b"foo"`) can be used
75 /// instead. They are shorter but less discoverable than `as_bytes()`.
77 /// ### Known problems
78 /// `"str".as_bytes()` and the suggested replacement of `b"str"` are not
79 /// equivalent because they have different types. The former is `&[u8]`
80 /// while the latter is `&[u8; 3]`. That means in general they will have a
81 /// different set of methods and different trait implementations.
84 /// fn f(v: Vec<u8>) {}
86 /// f("...".as_bytes().to_owned()); // works
87 /// f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>
89 /// fn g(r: impl std::io::Read) {}
91 /// g("...".as_bytes()); // works
92 /// g(b"..."); // does not work
95 /// The actual equivalent of `"str".as_bytes()` with the same type is not
96 /// `b"str"` but `&b"str"[..]`, which is a great deal of punctuation and not
97 /// more readable than a function call.
102 /// let bs = "a byte string".as_bytes();
105 /// let bs = b"a byte string";
107 #[clippy::version = "pre 1.29.0"]
108 pub STRING_LIT_AS_BYTES,
110 "calling `as_bytes` on a string literal instead of using a byte string literal"
113 declare_clippy_lint! {
115 /// Checks for slice operations on strings
117 /// ### Why is this bad?
118 /// UTF-8 characters span multiple bytes, and it is easy to inadvertently confuse character
119 /// counts and string indices. This may lead to panics, and should warrant some test cases
120 /// containing wide UTF-8 characters. This lint is most useful in code that should avoid
121 /// panics at all costs.
123 /// ### Known problems
124 /// Probably lots of false positives. If an index comes from a known valid position (e.g.
125 /// obtained via `char_indices` over the same string), it is totally OK.
128 /// ```rust,should_panic
129 /// &"Ölkanne"[1..];
131 #[clippy::version = "1.58.0"]
137 declare_lint_pass!(StringAdd => [STRING_ADD, STRING_ADD_ASSIGN, STRING_SLICE]);
139 impl<'tcx> LateLintPass<'tcx> for StringAdd {
140 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
141 if in_external_macro(cx.sess(), e.span) {
147 node: BinOpKind::Add, ..
152 if is_string(cx, left) {
153 if !is_lint_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
154 let parent = get_parent_expr(cx, e);
155 if let Some(p) = parent {
156 if let ExprKind::Assign(target, _, _) = p.kind {
157 // avoid duplicate matches
158 if SpanlessEq::new(cx).eq_expr(target, left) {
168 "you added something to a string. Consider using `String::push_str()` instead",
172 ExprKind::Assign(target, src, _) => {
173 if is_string(cx, target) && is_add(cx, src, target) {
178 "you assigned the result of adding something to this string. Consider using \
179 `String::push_str()` instead",
183 ExprKind::Index(target, _idx) => {
184 let e_ty = cx.typeck_results().expr_ty(target).peel_refs();
185 if matches!(e_ty.kind(), ty::Str) || is_type_diagnostic_item(cx, e_ty, sym::String) {
190 "indexing into a string may panic if the index is within a UTF-8 character",
199 fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
200 is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), sym::String)
203 fn is_add(cx: &LateContext<'_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {
204 match peel_blocks(src).kind {
207 node: BinOpKind::Add, ..
211 ) => SpanlessEq::new(cx).eq_expr(target, left),
216 declare_clippy_lint! {
218 /// Check if the string is transformed to byte array and casted back to string.
220 /// ### Why is this bad?
221 /// It's unnecessary, the string can be used directly.
225 /// let _ = std::str::from_utf8(&"Hello World!".as_bytes()[6..11]).unwrap();
227 /// could be written as
229 /// let _ = &"Hello World!"[6..11];
231 #[clippy::version = "1.50.0"]
232 pub STRING_FROM_UTF8_AS_BYTES,
234 "casting string slices to byte slices and back"
237 // Max length a b"foo" string can take
238 const MAX_LENGTH_BYTE_STRING_LIT: usize = 32;
240 declare_lint_pass!(StringLitAsBytes => [STRING_LIT_AS_BYTES, STRING_FROM_UTF8_AS_BYTES]);
242 impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
243 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
244 use rustc_ast::LitKind;
247 // Find std::str::converts::from_utf8
248 if let Some(args) = match_function_call(cx, e, &paths::STR_FROM_UTF8);
250 // Find string::as_bytes
251 if let ExprKind::AddrOf(BorrowKind::Ref, _, args) = args[0].kind;
252 if let ExprKind::Index(left, right) = args.kind;
253 let (method_names, expressions, _) = method_calls(left, 1);
254 if method_names.len() == 1;
255 if expressions.len() == 1;
256 if expressions[0].len() == 1;
257 if method_names[0] == sym!(as_bytes);
260 if let ExprKind::Struct(QPath::LangItem(LangItem::Range, ..), _, _) = right.kind;
263 let mut applicability = Applicability::MachineApplicable;
264 let string_expression = &expressions[0][0];
266 let snippet_app = snippet_with_applicability(
268 string_expression.span, "..",
274 STRING_FROM_UTF8_AS_BYTES,
276 "calling a slice of `as_bytes()` with `from_utf8` should be not necessary",
278 format!("Some(&{}[{}])", snippet_app, snippet(cx, right.span, "..")),
285 if let ExprKind::MethodCall(path, args, _) = &e.kind;
286 if path.ident.name == sym!(as_bytes);
287 if let ExprKind::Lit(lit) = &args[0].kind;
288 if let LitKind::Str(lit_content, _) = &lit.node;
290 let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
291 let mut applicability = Applicability::MachineApplicable;
292 if callsite.starts_with("include_str!") {
297 "calling `as_bytes()` on `include_str!(..)`",
298 "consider using `include_bytes!(..)` instead",
299 snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
306 } else if lit_content.as_str().is_ascii()
307 && lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
308 && !args[0].span.from_expansion()
314 "calling `as_bytes()` on a string literal",
315 "consider using a byte string literal instead",
318 snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
327 if let ExprKind::MethodCall(path, [recv], _) = &e.kind;
328 if path.ident.name == sym!(into_bytes);
329 if let ExprKind::MethodCall(path, [recv], _) = &recv.kind;
330 if matches!(path.ident.name.as_str(), "to_owned" | "to_string");
331 if let ExprKind::Lit(lit) = &recv.kind;
332 if let LitKind::Str(lit_content, _) = &lit.node;
334 if lit_content.as_str().is_ascii();
335 if lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT;
336 if !recv.span.from_expansion();
338 let mut applicability = Applicability::MachineApplicable;
344 "calling `into_bytes()` on a string literal",
345 "consider using a byte string literal instead",
348 snippet_with_applicability(cx, recv.span, r#""..""#, &mut applicability)
357 declare_clippy_lint! {
359 /// This lint checks for `.to_string()` method calls on values of type `&str`.
361 /// ### Why is this bad?
362 /// The `to_string` method is also used on other types to convert them to a string.
363 /// When called on a `&str` it turns the `&str` into the owned variant `String`, which can be better
364 /// expressed with `.to_owned()`.
368 /// // example code where clippy issues a warning
369 /// let _ = "str".to_string();
373 /// // example code which does not raise clippy warning
374 /// let _ = "str".to_owned();
376 #[clippy::version = "pre 1.29.0"]
379 "using `to_string()` on a `&str`, which should be `to_owned()`"
382 declare_lint_pass!(StrToString => [STR_TO_STRING]);
384 impl<'tcx> LateLintPass<'tcx> for StrToString {
385 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
387 if let ExprKind::MethodCall(path, [self_arg, ..], _) = &expr.kind;
388 if path.ident.name == sym!(to_string);
389 let ty = cx.typeck_results().expr_ty(self_arg);
390 if let ty::Ref(_, ty, ..) = ty.kind();
391 if *ty.kind() == ty::Str;
397 "`to_string()` called on a `&str`",
399 "consider using `.to_owned()`",
406 declare_clippy_lint! {
408 /// This lint checks for `.to_string()` method calls on values of type `String`.
410 /// ### Why is this bad?
411 /// The `to_string` method is also used on other types to convert them to a string.
412 /// When called on a `String` it only clones the `String`, which can be better expressed with `.clone()`.
416 /// // example code where clippy issues a warning
417 /// let msg = String::from("Hello World");
418 /// let _ = msg.to_string();
422 /// // example code which does not raise clippy warning
423 /// let msg = String::from("Hello World");
424 /// let _ = msg.clone();
426 #[clippy::version = "pre 1.29.0"]
427 pub STRING_TO_STRING,
429 "using `to_string()` on a `String`, which should be `clone()`"
432 declare_lint_pass!(StringToString => [STRING_TO_STRING]);
434 impl<'tcx> LateLintPass<'tcx> for StringToString {
435 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
437 if let ExprKind::MethodCall(path, [self_arg, ..], _) = &expr.kind;
438 if path.ident.name == sym!(to_string);
439 let ty = cx.typeck_results().expr_ty(self_arg);
440 if is_type_diagnostic_item(cx, ty, sym::String);
446 "`to_string()` called on a `String`",
448 "consider using `.clone()`",