rust-clippy/clippy_lints/src/strings.rs

388 lines
14 KiB
Rust

use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, LangItem, QPath};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
use rustc_span::sym;
use if_chain::if_chain;
use crate::utils::SpanlessEq;
use crate::utils::{
get_parent_expr, is_allowed, is_type_diagnostic_item, match_function_call, method_calls, paths, span_lint,
span_lint_and_help, span_lint_and_sugg,
};
declare_clippy_lint! {
/// **What it does:** Checks for string appends of the form `x = x + y` (without
/// `let`!).
///
/// **Why is this bad?** It's not really bad, but some people think that the
/// `.push_str(_)` method is more readable.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let mut x = "Hello".to_owned();
/// x = x + ", World";
///
/// // More readable
/// x += ", World";
/// x.push_str(", World");
/// ```
pub STRING_ADD_ASSIGN,
pedantic,
"using `x = x + ..` where x is a `String` instead of `push_str()`"
}
declare_clippy_lint! {
/// **What it does:** Checks for all instances of `x + _` where `x` is of type
/// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
/// match.
///
/// **Why is this bad?** It's not bad in and of itself. However, this particular
/// `Add` implementation is asymmetric (the other operand need not be `String`,
/// but `x` does), while addition as mathematically defined is symmetric, also
/// the `String::push_str(_)` function is a perfectly good replacement.
/// Therefore, some dislike it and wish not to have it in their code.
///
/// That said, other people think that string addition, having a long tradition
/// in other languages is actually fine, which is why we decided to make this
/// particular lint `allow` by default.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x = "Hello".to_owned();
/// x + ", World";
/// ```
pub STRING_ADD,
restriction,
"using `x + ..` where x is a `String` instead of `push_str()`"
}
declare_clippy_lint! {
/// **What it does:** Checks for the `as_bytes` method called on string literals
/// that contain only ASCII characters.
///
/// **Why is this bad?** Byte string literals (e.g., `b"foo"`) can be used
/// instead. They are shorter but less discoverable than `as_bytes()`.
///
/// **Known Problems:**
/// `"str".as_bytes()` and the suggested replacement of `b"str"` are not
/// equivalent because they have different types. The former is `&[u8]`
/// while the latter is `&[u8; 3]`. That means in general they will have a
/// different set of methods and different trait implementations.
///
/// ```compile_fail
/// fn f(v: Vec<u8>) {}
///
/// f("...".as_bytes().to_owned()); // works
/// f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>
///
/// fn g(r: impl std::io::Read) {}
///
/// g("...".as_bytes()); // works
/// g(b"..."); // does not work
/// ```
///
/// The actual equivalent of `"str".as_bytes()` with the same type is not
/// `b"str"` but `&b"str"[..]`, which is a great deal of punctuation and not
/// more readable than a function call.
///
/// **Example:**
/// ```rust
/// // Bad
/// let bs = "a byte string".as_bytes();
///
/// // Good
/// let bs = b"a byte string";
/// ```
pub STRING_LIT_AS_BYTES,
nursery,
"calling `as_bytes` on a string literal instead of using a byte string literal"
}
declare_lint_pass!(StringAdd => [STRING_ADD, STRING_ADD_ASSIGN]);
impl<'tcx> LateLintPass<'tcx> for StringAdd {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
if in_external_macro(cx.sess(), e.span) {
return;
}
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
ref left,
_,
) = e.kind
{
if is_string(cx, left) {
if !is_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
let parent = get_parent_expr(cx, e);
if let Some(p) = parent {
if let ExprKind::Assign(ref target, _, _) = p.kind {
// avoid duplicate matches
if SpanlessEq::new(cx).eq_expr(target, left) {
return;
}
}
}
}
span_lint(
cx,
STRING_ADD,
e.span,
"you added something to a string. Consider using `String::push_str()` instead",
);
}
} else if let ExprKind::Assign(ref target, ref src, _) = e.kind {
if is_string(cx, target) && is_add(cx, src, target) {
span_lint(
cx,
STRING_ADD_ASSIGN,
e.span,
"you assigned the result of adding something to this string. Consider using \
`String::push_str()` instead",
);
}
}
}
}
fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), sym::string_type)
}
fn is_add(cx: &LateContext<'_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {
match src.kind {
ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
ref left,
_,
) => SpanlessEq::new(cx).eq_expr(target, left),
ExprKind::Block(ref block, _) => {
block.stmts.is_empty() && block.expr.as_ref().map_or(false, |expr| is_add(cx, expr, target))
},
_ => false,
}
}
declare_clippy_lint! {
/// **What it does:** Check if the string is transformed to byte array and casted back to string.
///
/// **Why is this bad?** It's unnecessary, the string can be used directly.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let _ = std::str::from_utf8(&"Hello World!".as_bytes()[6..11]).unwrap();
/// ```
/// could be written as
/// ```rust
/// let _ = &"Hello World!"[6..11];
/// ```
pub STRING_FROM_UTF8_AS_BYTES,
complexity,
"casting string slices to byte slices and back"
}
// Max length a b"foo" string can take
const MAX_LENGTH_BYTE_STRING_LIT: usize = 32;
declare_lint_pass!(StringLitAsBytes => [STRING_LIT_AS_BYTES, STRING_FROM_UTF8_AS_BYTES]);
impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
use crate::utils::{snippet, snippet_with_applicability};
use rustc_ast::LitKind;
if_chain! {
// Find std::str::converts::from_utf8
if let Some(args) = match_function_call(cx, e, &paths::STR_FROM_UTF8);
// Find string::as_bytes
if let ExprKind::AddrOf(BorrowKind::Ref, _, ref args) = args[0].kind;
if let ExprKind::Index(ref left, ref right) = args.kind;
let (method_names, expressions, _) = method_calls(left, 1);
if method_names.len() == 1;
if expressions.len() == 1;
if expressions[0].len() == 1;
if method_names[0] == sym!(as_bytes);
// Check for slicer
if let ExprKind::Struct(QPath::LangItem(LangItem::Range, _), _, _) = right.kind;
then {
let mut applicability = Applicability::MachineApplicable;
let string_expression = &expressions[0][0];
let snippet_app = snippet_with_applicability(
cx,
string_expression.span, "..",
&mut applicability,
);
span_lint_and_sugg(
cx,
STRING_FROM_UTF8_AS_BYTES,
e.span,
"calling a slice of `as_bytes()` with `from_utf8` should be not necessary",
"try",
format!("Some(&{}[{}])", snippet_app, snippet(cx, right.span, "..")),
applicability
)
}
}
if_chain! {
if let ExprKind::MethodCall(path, _, args, _) = &e.kind;
if path.ident.name == sym!(as_bytes);
if let ExprKind::Lit(lit) = &args[0].kind;
if let LitKind::Str(lit_content, _) = &lit.node;
then {
let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
let mut applicability = Applicability::MachineApplicable;
if callsite.starts_with("include_str!") {
span_lint_and_sugg(
cx,
STRING_LIT_AS_BYTES,
e.span,
"calling `as_bytes()` on `include_str!(..)`",
"consider using `include_bytes!(..)` instead",
snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
"include_str",
"include_bytes",
1,
),
applicability,
);
} else if lit_content.as_str().is_ascii()
&& lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
&& !args[0].span.from_expansion()
{
span_lint_and_sugg(
cx,
STRING_LIT_AS_BYTES,
e.span,
"calling `as_bytes()` on a string literal",
"consider using a byte string literal instead",
format!(
"b{}",
snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
),
applicability,
);
}
}
}
}
}
declare_clippy_lint! {
/// **What it does:** This lint checks for `.to_string()` method calls on values of type `&str`.
///
/// **Why is this bad?** The `to_string` method is also used on other types to convert them to a string.
/// When called on a `&str` it turns the `&str` into the owned variant `String`, which can be better
/// expressed with `.to_owned()`.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// // example code where clippy issues a warning
/// let _ = "str".to_string();
/// ```
/// Use instead:
/// ```rust
/// // example code which does not raise clippy warning
/// let _ = "str".to_owned();
/// ```
pub STR_TO_STRING,
restriction,
"using `to_string()` on a `&str`, which should be `to_owned()`"
}
declare_lint_pass!(StrToString => [STR_TO_STRING]);
impl LateLintPass<'_> for StrToString {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
if path.ident.name == sym!(to_string);
let ty = cx.typeck_results().expr_ty(&args[0]);
if let ty::Ref(_, ty, ..) = ty.kind();
if *ty.kind() == ty::Str;
then {
span_lint_and_help(
cx,
STR_TO_STRING,
expr.span,
"`to_string()` called on a `&str`",
None,
"consider using `.to_owned()`",
);
}
}
}
}
declare_clippy_lint! {
/// **What it does:** This lint checks for `.to_string()` method calls on values of type `String`.
///
/// **Why is this bad?** The `to_string` method is also used on other types to convert them to a string.
/// When called on a `String` it only clones the `String`, which can be better expressed with `.clone()`.
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// // example code where clippy issues a warning
/// let msg = String::from("Hello World");
/// let _ = msg.to_string();
/// ```
/// Use instead:
/// ```rust
/// // example code which does not raise clippy warning
/// let msg = String::from("Hello World");
/// let _ = msg.clone();
/// ```
pub STRING_TO_STRING,
restriction,
"using `to_string()` on a `String`, which should be `clone()`"
}
declare_lint_pass!(StringToString => [STRING_TO_STRING]);
impl LateLintPass<'_> for StringToString {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
if_chain! {
if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
if path.ident.name == sym!(to_string);
let ty = cx.typeck_results().expr_ty(&args[0]);
if is_type_diagnostic_item(cx, ty, sym::string_type);
then {
span_lint_and_help(
cx,
STRING_TO_STRING,
expr.span,
"`to_string()` called on a `String`",
None,
"consider using `.clone()`",
);
}
}
}
}