src/tools/clippy/clippy_lints/src/strings.rs

   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::SpanlessEq;
   5 use clippy_utils::{get_parent_expr, is_lint_allowed, match_function_call, method_calls, paths};
   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;
  11 use rustc_middle::ty;
  12 use rustc_session::{declare_lint_pass, declare_tool_lint};
  13 use rustc_span::source_map::Spanned;
  14 use rustc_span::sym;
  15
  16 declare_clippy_lint! {
  17     /// **What it does:** Checks for string appends of the form `x = x + y` (without
  18     /// `let`!).
  19     ///
  20     /// **Why is this bad?** It's not really bad, but some people think that the
  21     /// `.push_str(_)` method is more readable.
  22     ///
  23     /// **Known problems:** None.
  24     ///
  25     /// **Example:**
  26     ///
  27     /// ```rust
  28     /// let mut x = "Hello".to_owned();
  29     /// x = x + ", World";
  30     ///
  31     /// // More readable
  32     /// x += ", World";
  33     /// x.push_str(", World");
  34     /// ```
  35     pub STRING_ADD_ASSIGN,
  36     pedantic,
  37     "using `x = x + ..` where x is a `String` instead of `push_str()`"
  38 }
  39
  40 declare_clippy_lint! {
  41     /// **What it does:** Checks for all instances of `x + _` where `x` is of type
  42     /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
  43     /// match.
  44     ///
  45     /// **Why is this bad?** It's not bad in and of itself. However, this particular
  46     /// `Add` implementation is asymmetric (the other operand need not be `String`,
  47     /// but `x` does), while addition as mathematically defined is symmetric, also
  48     /// the `String::push_str(_)` function is a perfectly good replacement.
  49     /// Therefore, some dislike it and wish not to have it in their code.
  50     ///
  51     /// That said, other people think that string addition, having a long tradition
  52     /// in other languages is actually fine, which is why we decided to make this
  53     /// particular lint `allow` by default.
  54     ///
  55     /// **Known problems:** None.
  56     ///
  57     /// **Example:**
  58     ///
  59     /// ```rust
  60     /// let x = "Hello".to_owned();
  61     /// x + ", World";
  62     /// ```
  63     pub STRING_ADD,
  64     restriction,
  65     "using `x + ..` where x is a `String` instead of `push_str()`"
  66 }
  67
  68 declare_clippy_lint! {
  69     /// **What it does:** Checks for the `as_bytes` method called on string literals
  70     /// that contain only ASCII characters.
  71     ///
  72     /// **Why is this bad?** Byte string literals (e.g., `b"foo"`) can be used
  73     /// instead. They are shorter but less discoverable than `as_bytes()`.
  74     ///
  75     /// **Known Problems:**
  76     /// `"str".as_bytes()` and the suggested replacement of `b"str"` are not
  77     /// equivalent because they have different types. The former is `&[u8]`
  78     /// while the latter is `&[u8; 3]`. That means in general they will have a
  79     /// different set of methods and different trait implementations.
  80     ///
  81     /// ```compile_fail
  82     /// fn f(v: Vec<u8>) {}
  83     ///
  84     /// f("...".as_bytes().to_owned()); // works
  85     /// f(b"...".to_owned()); // does not work, because arg is [u8; 3] not Vec<u8>
  86     ///
  87     /// fn g(r: impl std::io::Read) {}
  88     ///
  89     /// g("...".as_bytes()); // works
  90     /// g(b"..."); // does not work
  91     /// ```
  92     ///
  93     /// The actual equivalent of `"str".as_bytes()` with the same type is not
  94     /// `b"str"` but `&b"str"[..]`, which is a great deal of punctuation and not
  95     /// more readable than a function call.
  96     ///
  97     /// **Example:**
  98     /// ```rust
  99     /// // Bad
 100     /// let bs = "a byte string".as_bytes();
 101     ///
 102     /// // Good
 103     /// let bs = b"a byte string";
 104     /// ```
 105     pub STRING_LIT_AS_BYTES,
 106     nursery,
 107     "calling `as_bytes` on a string literal instead of using a byte string literal"
 108 }
 109
 110 declare_lint_pass!(StringAdd => [STRING_ADD, STRING_ADD_ASSIGN]);
 111
 112 impl<'tcx> LateLintPass<'tcx> for StringAdd {
 113     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 114         if in_external_macro(cx.sess(), e.span) {
 115             return;
 116         }
 117
 118         if let ExprKind::Binary(
 119             Spanned {
 120                 node: BinOpKind::Add, ..
 121             },
 122             left,
 123             _,
 124         ) = e.kind
 125         {
 126             if is_string(cx, left) {
 127                 if !is_lint_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
 128                     let parent = get_parent_expr(cx, e);
 129                     if let Some(p) = parent {
 130                         if let ExprKind::Assign(target, _, _) = p.kind {
 131                             // avoid duplicate matches
 132                             if SpanlessEq::new(cx).eq_expr(target, left) {
 133                                 return;
 134                             }
 135                         }
 136                     }
 137                 }
 138                 span_lint(
 139                     cx,
 140                     STRING_ADD,
 141                     e.span,
 142                     "you added something to a string. Consider using `String::push_str()` instead",
 143                 );
 144             }
 145         } else if let ExprKind::Assign(target, src, _) = e.kind {
 146             if is_string(cx, target) && is_add(cx, src, target) {
 147                 span_lint(
 148                     cx,
 149                     STRING_ADD_ASSIGN,
 150                     e.span,
 151                     "you assigned the result of adding something to this string. Consider using \
 152                      `String::push_str()` instead",
 153                 );
 154             }
 155         }
 156     }
 157 }
 158
 159 fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
 160     is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), sym::string_type)
 161 }
 162
 163 fn is_add(cx: &LateContext<'_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {
 164     match src.kind {
 165         ExprKind::Binary(
 166             Spanned {
 167                 node: BinOpKind::Add, ..
 168             },
 169             left,
 170             _,
 171         ) => SpanlessEq::new(cx).eq_expr(target, left),
 172         ExprKind::Block(block, _) => {
 173             block.stmts.is_empty() && block.expr.as_ref().map_or(false, |expr| is_add(cx, expr, target))
 174         },
 175         _ => false,
 176     }
 177 }
 178
 179 declare_clippy_lint! {
 180     /// **What it does:** Check if the string is transformed to byte array and casted back to string.
 181     ///
 182     /// **Why is this bad?** It's unnecessary, the string can be used directly.
 183     ///
 184     /// **Known problems:** None
 185     ///
 186     /// **Example:**
 187     /// ```rust
 188     /// let _ = std::str::from_utf8(&"Hello World!".as_bytes()[6..11]).unwrap();
 189     /// ```
 190     /// could be written as
 191     /// ```rust
 192     /// let _ = &"Hello World!"[6..11];
 193     /// ```
 194     pub STRING_FROM_UTF8_AS_BYTES,
 195     complexity,
 196     "casting string slices to byte slices and back"
 197 }
 198
 199 // Max length a b"foo" string can take
 200 const MAX_LENGTH_BYTE_STRING_LIT: usize = 32;
 201
 202 declare_lint_pass!(StringLitAsBytes => [STRING_LIT_AS_BYTES, STRING_FROM_UTF8_AS_BYTES]);
 203
 204 impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
 205     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
 206         use rustc_ast::LitKind;
 207
 208         if_chain! {
 209             // Find std::str::converts::from_utf8
 210             if let Some(args) = match_function_call(cx, e, &paths::STR_FROM_UTF8);
 211
 212             // Find string::as_bytes
 213             if let ExprKind::AddrOf(BorrowKind::Ref, _, args) = args[0].kind;
 214             if let ExprKind::Index(left, right) = args.kind;
 215             let (method_names, expressions, _) = method_calls(left, 1);
 216             if method_names.len() == 1;
 217             if expressions.len() == 1;
 218             if expressions[0].len() == 1;
 219             if method_names[0] == sym!(as_bytes);
 220
 221             // Check for slicer
 222             if let ExprKind::Struct(QPath::LangItem(LangItem::Range, _), _, _) = right.kind;
 223
 224             then {
 225                 let mut applicability = Applicability::MachineApplicable;
 226                 let string_expression = &expressions[0][0];
 227
 228                 let snippet_app = snippet_with_applicability(
 229                     cx,
 230                     string_expression.span, "..",
 231                     &mut applicability,
 232                 );
 233
 234                 span_lint_and_sugg(
 235                     cx,
 236                     STRING_FROM_UTF8_AS_BYTES,
 237                     e.span,
 238                     "calling a slice of `as_bytes()` with `from_utf8` should be not necessary",
 239                     "try",
 240                     format!("Some(&{}[{}])", snippet_app, snippet(cx, right.span, "..")),
 241                     applicability
 242                 )
 243             }
 244         }
 245
 246         if_chain! {
 247             if let ExprKind::MethodCall(path, _, args, _) = &e.kind;
 248             if path.ident.name == sym!(as_bytes);
 249             if let ExprKind::Lit(lit) = &args[0].kind;
 250             if let LitKind::Str(lit_content, _) = &lit.node;
 251             then {
 252                 let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
 253                 let mut applicability = Applicability::MachineApplicable;
 254                 if callsite.starts_with("include_str!") {
 255                     span_lint_and_sugg(
 256                         cx,
 257                         STRING_LIT_AS_BYTES,
 258                         e.span,
 259                         "calling `as_bytes()` on `include_str!(..)`",
 260                         "consider using `include_bytes!(..)` instead",
 261                         snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
 262                             "include_str",
 263                             "include_bytes",
 264                             1,
 265                         ),
 266                         applicability,
 267                     );
 268                 } else if lit_content.as_str().is_ascii()
 269                     && lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
 270                     && !args[0].span.from_expansion()
 271                 {
 272                     span_lint_and_sugg(
 273                         cx,
 274                         STRING_LIT_AS_BYTES,
 275                         e.span,
 276                         "calling `as_bytes()` on a string literal",
 277                         "consider using a byte string literal instead",
 278                         format!(
 279                             "b{}",
 280                             snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
 281                         ),
 282                         applicability,
 283                     );
 284                 }
 285             }
 286         }
 287
 288         if_chain! {
 289             if let ExprKind::MethodCall(path, _, [recv], _) = &e.kind;
 290             if path.ident.name == sym!(into_bytes);
 291             if let ExprKind::MethodCall(path, _, [recv], _) = &recv.kind;
 292             if matches!(&*path.ident.name.as_str(), "to_owned" | "to_string");
 293             if let ExprKind::Lit(lit) = &recv.kind;
 294             if let LitKind::Str(lit_content, _) = &lit.node;
 295
 296             if lit_content.as_str().is_ascii();
 297             if lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT;
 298             if !recv.span.from_expansion();
 299             then {
 300                 let mut applicability = Applicability::MachineApplicable;
 301
 302                 span_lint_and_sugg(
 303                     cx,
 304                     STRING_LIT_AS_BYTES,
 305                     e.span,
 306                     "calling `into_bytes()` on a string literal",
 307                     "consider using a byte string literal instead",
 308                     format!(
 309                         "b{}.to_vec()",
 310                         snippet_with_applicability(cx, recv.span, r#""..""#, &mut applicability)
 311                     ),
 312                     applicability,
 313                 );
 314             }
 315         }
 316     }
 317 }
 318
 319 declare_clippy_lint! {
 320     /// **What it does:** This lint checks for `.to_string()` method calls on values of type `&str`.
 321     ///
 322     /// **Why is this bad?** The `to_string` method is also used on other types to convert them to a string.
 323     /// When called on a `&str` it turns the `&str` into the owned variant `String`, which can be better
 324     /// expressed with `.to_owned()`.
 325     ///
 326     /// **Known problems:** None.
 327     ///
 328     /// **Example:**
 329     ///
 330     /// ```rust
 331     /// // example code where clippy issues a warning
 332     /// let _ = "str".to_string();
 333     /// ```
 334     /// Use instead:
 335     /// ```rust
 336     /// // example code which does not raise clippy warning
 337     /// let _ = "str".to_owned();
 338     /// ```
 339     pub STR_TO_STRING,
 340     restriction,
 341     "using `to_string()` on a `&str`, which should be `to_owned()`"
 342 }
 343
 344 declare_lint_pass!(StrToString => [STR_TO_STRING]);
 345
 346 impl LateLintPass<'_> for StrToString {
 347     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
 348         if_chain! {
 349             if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
 350             if path.ident.name == sym!(to_string);
 351             let ty = cx.typeck_results().expr_ty(&args[0]);
 352             if let ty::Ref(_, ty, ..) = ty.kind();
 353             if *ty.kind() == ty::Str;
 354             then {
 355                 span_lint_and_help(
 356                     cx,
 357                     STR_TO_STRING,
 358                     expr.span,
 359                     "`to_string()` called on a `&str`",
 360                     None,
 361                     "consider using `.to_owned()`",
 362                 );
 363             }
 364         }
 365     }
 366 }
 367
 368 declare_clippy_lint! {
 369     /// **What it does:** This lint checks for `.to_string()` method calls on values of type `String`.
 370     ///
 371     /// **Why is this bad?** The `to_string` method is also used on other types to convert them to a string.
 372     /// When called on a `String` it only clones the `String`, which can be better expressed with `.clone()`.
 373     /// **Known problems:** None.
 374     ///
 375     /// **Example:**
 376     ///
 377     /// ```rust
 378     /// // example code where clippy issues a warning
 379     /// let msg = String::from("Hello World");
 380     /// let _ = msg.to_string();
 381     /// ```
 382     /// Use instead:
 383     /// ```rust
 384     /// // example code which does not raise clippy warning
 385     /// let msg = String::from("Hello World");
 386     /// let _ = msg.clone();
 387     /// ```
 388     pub STRING_TO_STRING,
 389     restriction,
 390     "using `to_string()` on a `String`, which should be `clone()`"
 391 }
 392
 393 declare_lint_pass!(StringToString => [STRING_TO_STRING]);
 394
 395 impl LateLintPass<'_> for StringToString {
 396     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
 397         if_chain! {
 398             if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
 399             if path.ident.name == sym!(to_string);
 400             let ty = cx.typeck_results().expr_ty(&args[0]);
 401             if is_type_diagnostic_item(cx, ty, sym::string_type);
 402             then {
 403                 span_lint_and_help(
 404                     cx,
 405                     STRING_TO_STRING,
 406                     expr.span,
 407                     "`to_string()` called on a `String`",
 408                     None,
 409                     "consider using `.clone()`",
 410                 );
 411             }
 412         }
 413     }
 414 }