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 /// **What it does:** Checks for string appends of the form `x = x + y` (without
  10 /// `let`!).
  11 ///
  12 /// **Why is this bad?** It's not really bad, but some people think that the
  13 /// `.push_str(_)` method is more readable.
  14 ///
  15 /// **Known problems:** None.
  16 ///
  17 /// **Example:**
  18 ///
  19 /// ```rust
  20 /// let mut x = "Hello".to_owned();
  21 /// x = x + ", World";
  22 /// ```
  23 declare_clippy_lint! {
  24     pub STRING_ADD_ASSIGN,
  25     pedantic,
  26     "using `x = x + ..` where x is a `String` instead of `push_str()`"
  27 }
  28
  29 /// **What it does:** Checks for all instances of `x + _` where `x` is of type
  30 /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
  31 /// match.
  32 ///
  33 /// **Why is this bad?** It's not bad in and of itself. However, this particular
  34 /// `Add` implementation is asymmetric (the other operand need not be `String`,
  35 /// but `x` does), while addition as mathematically defined is symmetric, also
  36 /// the `String::push_str(_)` function is a perfectly good replacement.
  37 /// Therefore some dislike it and wish not to have it in their code.
  38 ///
  39 /// That said, other people think that string addition, having a long tradition
  40 /// in other languages is actually fine, which is why we decided to make this
  41 /// particular lint `allow` by default.
  42 ///
  43 /// **Known problems:** None.
  44 ///
  45 /// **Example:**
  46 ///
  47 /// ```rust
  48 /// let x = "Hello".to_owned();
  49 /// x + ", World"
  50 /// ```
  51 declare_clippy_lint! {
  52     pub STRING_ADD,
  53     restriction,
  54     "using `x + ..` where x is a `String` instead of `push_str()`"
  55 }
  56
  57 /// **What it does:** Checks for the `as_bytes` method called on string literals
  58 /// that contain only ASCII characters.
  59 ///
  60 /// **Why is this bad?** Byte string literals (e.g. `b"foo"`) can be used
  61 /// instead. They are shorter but less discoverable than `as_bytes()`.
  62 ///
  63 /// **Known Problems:** None.
  64 ///
  65 /// **Example:**
  66 /// ```rust
  67 /// let bs = "a byte string".as_bytes();
  68 /// ```
  69 declare_clippy_lint! {
  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
  84 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringAdd {
  85     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  86         if let ExprKind::Binary(
  87             Spanned {
  88                 node: BinOpKind::Add, ..
  89             },
  90             ref left,
  91             _,
  92         ) = e.node
  93         {
  94             if is_string(cx, left) {
  95                 if !is_allowed(cx, STRING_ADD_ASSIGN, e.id) {
  96                     let parent = get_parent_expr(cx, e);
  97                     if let Some(p) = parent {
  98                         if let ExprKind::Assign(ref target, _) = p.node {
  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.node {
 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.node {
 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 #[derive(Copy, Clone)]
 148 pub struct StringLitAsBytes;
 149
 150 impl LintPass for StringLitAsBytes {
 151     fn get_lints(&self) -> LintArray {
 152         lint_array!(STRING_LIT_AS_BYTES)
 153     }
 154 }
 155
 156 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringLitAsBytes {
 157     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 158         use crate::utils::{in_macro, snippet, snippet_with_applicability};
 159         use syntax::ast::{LitKind, StrStyle};
 160
 161         if let ExprKind::MethodCall(ref path, _, ref args) = e.node {
 162             if path.ident.name == "as_bytes" {
 163                 if let ExprKind::Lit(ref lit) = args[0].node {
 164                     if let LitKind::Str(ref lit_content, style) = lit.node {
 165                         let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
 166                         let expanded = if let StrStyle::Raw(n) = style {
 167                             let term = (0..n).map(|_| '#').collect::<String>();
 168                             format!("r{0}\"{1}\"{0}", term, lit_content.as_str())
 169                         } else {
 170                             format!("\"{}\"", lit_content.as_str())
 171                         };
 172                         let mut applicability = Applicability::MachineApplicable;
 173                         if callsite.starts_with("include_str!") {
 174                             span_lint_and_sugg(
 175                                 cx,
 176                                 STRING_LIT_AS_BYTES,
 177                                 e.span,
 178                                 "calling `as_bytes()` on `include_str!(..)`",
 179                                 "consider using `include_bytes!(..)` instead",
 180                                 snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
 181                                     "include_str",
 182                                     "include_bytes",
 183                                     1,
 184                                 ),
 185                                 applicability,
 186                             );
 187                         } else if callsite == expanded
 188                             && lit_content.as_str().chars().all(|c| c.is_ascii())
 189                             && !in_macro(args[0].span)
 190                         {
 191                             span_lint_and_sugg(
 192                                 cx,
 193                                 STRING_LIT_AS_BYTES,
 194                                 e.span,
 195                                 "calling `as_bytes()` on a string literal",
 196                                 "consider using a byte string literal instead",
 197                                 format!(
 198                                     "b{}",
 199                                     snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
 200                                 ),
 201                                 applicability,
 202                             );
 203                         }
 204                     }
 205                 }
 206             }
 207         }
 208     }
 209 }