clippy_lints/src/strings.rs

   1 use crate::utils::SpanlessEq;
   2 use crate::utils::{get_parent_expr, is_allowed, match_type, paths, span_lint, span_lint_and_sugg, walk_ptrs_ty};
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc::{declare_tool_lint, lint_array};
   6 use rustc_errors::Applicability;
   7 use syntax::source_map::Spanned;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for string appends of the form `x = x + y` (without
  11     /// `let`!).
  12     ///
  13     /// **Why is this bad?** It's not really bad, but some people think that the
  14     /// `.push_str(_)` method is more readable.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     ///
  20     /// ```rust
  21     /// let mut x = "Hello".to_owned();
  22     /// x = x + ", World";
  23     /// ```
  24     pub STRING_ADD_ASSIGN,
  25     pedantic,
  26     "using `x = x + ..` where x is a `String` instead of `push_str()`"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks for all instances of `x + _` where `x` is of type
  31     /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
  32     /// match.
  33     ///
  34     /// **Why is this bad?** It's not bad in and of itself. However, this particular
  35     /// `Add` implementation is asymmetric (the other operand need not be `String`,
  36     /// but `x` does), while addition as mathematically defined is symmetric, also
  37     /// the `String::push_str(_)` function is a perfectly good replacement.
  38     /// Therefore some dislike it and wish not to have it in their code.
  39     ///
  40     /// That said, other people think that string addition, having a long tradition
  41     /// in other languages is actually fine, which is why we decided to make this
  42     /// particular lint `allow` by default.
  43     ///
  44     /// **Known problems:** None.
  45     ///
  46     /// **Example:**
  47     ///
  48     /// ```rust
  49     /// let x = "Hello".to_owned();
  50     /// x + ", World"
  51     /// ```
  52     pub STRING_ADD,
  53     restriction,
  54     "using `x + ..` where x is a `String` instead of `push_str()`"
  55 }
  56
  57 declare_clippy_lint! {
  58     /// **What it does:** Checks for the `as_bytes` method called on string literals
  59     /// that contain only ASCII characters.
  60     ///
  61     /// **Why is this bad?** Byte string literals (e.g. `b"foo"`) can be used
  62     /// instead. They are shorter but less discoverable than `as_bytes()`.
  63     ///
  64     /// **Known Problems:** None.
  65     ///
  66     /// **Example:**
  67     /// ```rust
  68     /// let bs = "a byte string".as_bytes();
  69     /// ```
  70     pub STRING_LIT_AS_BYTES,
  71     style,
  72     "calling `as_bytes` on a string literal instead of using a byte string literal"
  73 }
  74
  75 #[derive(Copy, Clone)]
  76 pub struct StringAdd;
  77
  78 impl LintPass for StringAdd {
  79     fn get_lints(&self) -> LintArray {
  80         lint_array!(STRING_ADD, STRING_ADD_ASSIGN)
  81     }
  82
  83     fn name(&self) -> &'static str {
  84         "StringAdd"
  85     }
  86 }
  87
  88 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringAdd {
  89     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  90         if let ExprKind::Binary(
  91             Spanned {
  92                 node: BinOpKind::Add, ..
  93             },
  94             ref left,
  95             _,
  96         ) = e.node
  97         {
  98             if is_string(cx, left) {
  99                 if !is_allowed(cx, STRING_ADD_ASSIGN, e.hir_id) {
 100                     let parent = get_parent_expr(cx, e);
 101                     if let Some(p) = parent {
 102                         if let ExprKind::Assign(ref target, _) = p.node {
 103                             // avoid duplicate matches
 104                             if SpanlessEq::new(cx).eq_expr(target, left) {
 105                                 return;
 106                             }
 107                         }
 108                     }
 109                 }
 110                 span_lint(
 111                     cx,
 112                     STRING_ADD,
 113                     e.span,
 114                     "you added something to a string. Consider using `String::push_str()` instead",
 115                 );
 116             }
 117         } else if let ExprKind::Assign(ref target, ref src) = e.node {
 118             if is_string(cx, target) && is_add(cx, src, target) {
 119                 span_lint(
 120                     cx,
 121                     STRING_ADD_ASSIGN,
 122                     e.span,
 123                     "you assigned the result of adding something to this string. Consider using \
 124                      `String::push_str()` instead",
 125                 );
 126             }
 127         }
 128     }
 129 }
 130
 131 fn is_string(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
 132     match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(e)), &paths::STRING)
 133 }
 134
 135 fn is_add(cx: &LateContext<'_, '_>, src: &Expr, target: &Expr) -> bool {
 136     match src.node {
 137         ExprKind::Binary(
 138             Spanned {
 139                 node: BinOpKind::Add, ..
 140             },
 141             ref left,
 142             _,
 143         ) => SpanlessEq::new(cx).eq_expr(target, left),
 144         ExprKind::Block(ref block, _) => {
 145             block.stmts.is_empty() && block.expr.as_ref().map_or(false, |expr| is_add(cx, expr, target))
 146         },
 147         _ => false,
 148     }
 149 }
 150
 151 #[derive(Copy, Clone)]
 152 pub struct StringLitAsBytes;
 153
 154 impl LintPass for StringLitAsBytes {
 155     fn get_lints(&self) -> LintArray {
 156         lint_array!(STRING_LIT_AS_BYTES)
 157     }
 158
 159     fn name(&self) -> &'static str {
 160         "StringLiteralAsBytes"
 161     }
 162 }
 163
 164 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringLitAsBytes {
 165     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 166         use crate::utils::{in_macro, snippet, snippet_with_applicability};
 167         use syntax::ast::{LitKind, StrStyle};
 168
 169         if let ExprKind::MethodCall(ref path, _, ref args) = e.node {
 170             if path.ident.name == "as_bytes" {
 171                 if let ExprKind::Lit(ref lit) = args[0].node {
 172                     if let LitKind::Str(ref lit_content, style) = lit.node {
 173                         let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
 174                         let expanded = if let StrStyle::Raw(n) = style {
 175                             let term = (0..n).map(|_| '#').collect::<String>();
 176                             format!("r{0}\"{1}\"{0}", term, lit_content.as_str())
 177                         } else {
 178                             format!("\"{}\"", lit_content.as_str())
 179                         };
 180                         let mut applicability = Applicability::MachineApplicable;
 181                         if callsite.starts_with("include_str!") {
 182                             span_lint_and_sugg(
 183                                 cx,
 184                                 STRING_LIT_AS_BYTES,
 185                                 e.span,
 186                                 "calling `as_bytes()` on `include_str!(..)`",
 187                                 "consider using `include_bytes!(..)` instead",
 188                                 snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
 189                                     "include_str",
 190                                     "include_bytes",
 191                                     1,
 192                                 ),
 193                                 applicability,
 194                             );
 195                         } else if callsite == expanded
 196                             && lit_content.as_str().chars().all(|c| c.is_ascii())
 197                             && !in_macro(args[0].span)
 198                         {
 199                             span_lint_and_sugg(
 200                                 cx,
 201                                 STRING_LIT_AS_BYTES,
 202                                 e.span,
 203                                 "calling `as_bytes()` on a string literal",
 204                                 "consider using a byte string literal instead",
 205                                 format!(
 206                                     "b{}",
 207                                     snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
 208                                 ),
 209                                 applicability,
 210                             );
 211                         }
 212                     }
 213                 }
 214             }
 215         }
 216     }
 217 }