clippy_lints/src/strings.rs

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