clippy_lints/src/strings.rs

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