clippy_lints/src/strings.rs

   1 use rustc_errors::Applicability;
   2 use rustc_hir::{BinOpKind, Expr, ExprKind};
   3 use rustc_lint::{LateContext, LateLintPass, LintContext};
   4 use rustc_middle::lint::in_external_macro;
   5 use rustc_session::{declare_lint_pass, declare_tool_lint};
   6 use rustc_span::source_map::Spanned;
   7
   8 use if_chain::if_chain;
   9
  10 use crate::utils::SpanlessEq;
  11 use crate::utils::{get_parent_expr, is_allowed, match_type, paths, span_lint, span_lint_and_sugg, walk_ptrs_ty};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for string appends of the form `x = x + y` (without
  15     /// `let`!).
  16     ///
  17     /// **Why is this bad?** It's not really bad, but some people think that the
  18     /// `.push_str(_)` method is more readable.
  19     ///
  20     /// **Known problems:** None.
  21     ///
  22     /// **Example:**
  23     ///
  24     /// ```rust
  25     /// let mut x = "Hello".to_owned();
  26     /// x = x + ", World";
  27     /// ```
  28     pub STRING_ADD_ASSIGN,
  29     pedantic,
  30     "using `x = x + ..` where x is a `String` instead of `push_str()`"
  31 }
  32
  33 declare_clippy_lint! {
  34     /// **What it does:** Checks for all instances of `x + _` where `x` is of type
  35     /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
  36     /// match.
  37     ///
  38     /// **Why is this bad?** It's not bad in and of itself. However, this particular
  39     /// `Add` implementation is asymmetric (the other operand need not be `String`,
  40     /// but `x` does), while addition as mathematically defined is symmetric, also
  41     /// the `String::push_str(_)` function is a perfectly good replacement.
  42     /// Therefore, some dislike it and wish not to have it in their code.
  43     ///
  44     /// That said, other people think that string addition, having a long tradition
  45     /// in other languages is actually fine, which is why we decided to make this
  46     /// particular lint `allow` by default.
  47     ///
  48     /// **Known problems:** None.
  49     ///
  50     /// **Example:**
  51     ///
  52     /// ```rust
  53     /// let x = "Hello".to_owned();
  54     /// x + ", World";
  55     /// ```
  56     pub STRING_ADD,
  57     restriction,
  58     "using `x + ..` where x is a `String` instead of `push_str()`"
  59 }
  60
  61 declare_clippy_lint! {
  62     /// **What it does:** Checks for the `as_bytes` method called on string literals
  63     /// that contain only ASCII characters.
  64     ///
  65     /// **Why is this bad?** Byte string literals (e.g., `b"foo"`) can be used
  66     /// instead. They are shorter but less discoverable than `as_bytes()`.
  67     ///
  68     /// **Known Problems:** None.
  69     ///
  70     /// **Example:**
  71     /// ```rust
  72     /// let bs = "a byte string".as_bytes();
  73     /// ```
  74     pub STRING_LIT_AS_BYTES,
  75     style,
  76     "calling `as_bytes` on a string literal instead of using a byte string literal"
  77 }
  78
  79 declare_lint_pass!(StringAdd => [STRING_ADD, STRING_ADD_ASSIGN]);
  80
  81 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringAdd {
  82     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
  83         if in_external_macro(cx.sess(), e.span) {
  84             return;
  85         }
  86
  87         if let ExprKind::Binary(
  88             Spanned {
  89                 node: BinOpKind::Add, ..
  90             },
  91             ref left,
  92             _,
  93         ) = e.kind
  94         {
  95             if is_string(cx, left) {
  96                 if !is_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
  97                     let parent = get_parent_expr(cx, e);
  98                     if let Some(p) = parent {
  99                         if let ExprKind::Assign(ref target, _, _) = p.kind {
 100                             // avoid duplicate matches
 101                             if SpanlessEq::new(cx).eq_expr(target, left) {
 102                                 return;
 103                             }
 104                         }
 105                     }
 106                 }
 107                 span_lint(
 108                     cx,
 109                     STRING_ADD,
 110                     e.span,
 111                     "you added something to a string. Consider using `String::push_str()` instead",
 112                 );
 113             }
 114         } else if let ExprKind::Assign(ref target, ref src, _) = e.kind {
 115             if is_string(cx, target) && is_add(cx, src, target) {
 116                 span_lint(
 117                     cx,
 118                     STRING_ADD_ASSIGN,
 119                     e.span,
 120                     "you assigned the result of adding something to this string. Consider using \
 121                      `String::push_str()` instead",
 122                 );
 123             }
 124         }
 125     }
 126 }
 127
 128 fn is_string(cx: &LateContext<'_, '_>, e: &Expr<'_>) -> bool {
 129     match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(e)), &paths::STRING)
 130 }
 131
 132 fn is_add(cx: &LateContext<'_, '_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {
 133     match src.kind {
 134         ExprKind::Binary(
 135             Spanned {
 136                 node: BinOpKind::Add, ..
 137             },
 138             ref left,
 139             _,
 140         ) => SpanlessEq::new(cx).eq_expr(target, left),
 141         ExprKind::Block(ref block, _) => {
 142             block.stmts.is_empty() && block.expr.as_ref().map_or(false, |expr| is_add(cx, expr, target))
 143         },
 144         _ => false,
 145     }
 146 }
 147
 148 // Max length a b"foo" string can take
 149 const MAX_LENGTH_BYTE_STRING_LIT: usize = 32;
 150
 151 declare_lint_pass!(StringLitAsBytes => [STRING_LIT_AS_BYTES]);
 152
 153 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringLitAsBytes {
 154     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
 155         use crate::utils::{snippet, snippet_with_applicability};
 156         use rustc_ast::ast::LitKind;
 157
 158         if_chain! {
 159             if let ExprKind::MethodCall(path, _, args) = &e.kind;
 160             if path.ident.name == sym!(as_bytes);
 161             if let ExprKind::Lit(lit) = &args[0].kind;
 162             if let LitKind::Str(lit_content, _) = &lit.node;
 163             then {
 164                 let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
 165                 let mut applicability = Applicability::MachineApplicable;
 166                 if callsite.starts_with("include_str!") {
 167                     span_lint_and_sugg(
 168                         cx,
 169                         STRING_LIT_AS_BYTES,
 170                         e.span,
 171                         "calling `as_bytes()` on `include_str!(..)`",
 172                         "consider using `include_bytes!(..)` instead",
 173                         snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
 174                             "include_str",
 175                             "include_bytes",
 176                             1,
 177                         ),
 178                         applicability,
 179                     );
 180                 } else if lit_content.as_str().is_ascii()
 181                     && lit_content.as_str().len() <= MAX_LENGTH_BYTE_STRING_LIT
 182                     && !args[0].span.from_expansion()
 183                 {
 184                     span_lint_and_sugg(
 185                         cx,
 186                         STRING_LIT_AS_BYTES,
 187                         e.span,
 188                         "calling `as_bytes()` on a string literal",
 189                         "consider using a byte string literal instead",
 190                         format!(
 191                             "b{}",
 192                             snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
 193                         ),
 194                         applicability,
 195                     );
 196                 }
 197             }
 198         }
 199     }
 200 }