clippy_lints/src/strings.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   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 use rustc::hir::*;
  13 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  14 use rustc::{declare_tool_lint, lint_array};
  15 use rustc_errors::Applicability;
  16 use syntax::source_map::Spanned;
  17
  18 /// **What it does:** Checks for string appends of the form `x = x + y` (without
  19 /// `let`!).
  20 ///
  21 /// **Why is this bad?** It's not really bad, but some people think that the
  22 /// `.push_str(_)` method is more readable.
  23 ///
  24 /// **Known problems:** None.
  25 ///
  26 /// **Example:**
  27 ///
  28 /// ```rust
  29 /// let mut x = "Hello".to_owned();
  30 /// x = x + ", World";
  31 /// ```
  32 declare_clippy_lint! {
  33     pub STRING_ADD_ASSIGN,
  34     pedantic,
  35     "using `x = x + ..` where x is a `String` instead of `push_str()`"
  36 }
  37
  38 /// **What it does:** Checks for all instances of `x + _` where `x` is of type
  39 /// `String`, but only if [`string_add_assign`](#string_add_assign) does *not*
  40 /// match.
  41 ///
  42 /// **Why is this bad?** It's not bad in and of itself. However, this particular
  43 /// `Add` implementation is asymmetric (the other operand need not be `String`,
  44 /// but `x` does), while addition as mathematically defined is symmetric, also
  45 /// the `String::push_str(_)` function is a perfectly good replacement.
  46 /// Therefore some dislike it and wish not to have it in their code.
  47 ///
  48 /// That said, other people think that string addition, having a long tradition
  49 /// in other languages is actually fine, which is why we decided to make this
  50 /// particular lint `allow` by default.
  51 ///
  52 /// **Known problems:** None.
  53 ///
  54 /// **Example:**
  55 ///
  56 /// ```rust
  57 /// let x = "Hello".to_owned();
  58 /// x + ", World"
  59 /// ```
  60 declare_clippy_lint! {
  61     pub STRING_ADD,
  62     restriction,
  63     "using `x + ..` where x is a `String` instead of `push_str()`"
  64 }
  65
  66 /// **What it does:** Checks for the `as_bytes` method called on string literals
  67 /// that contain only ASCII characters.
  68 ///
  69 /// **Why is this bad?** Byte string literals (e.g. `b"foo"`) can be used
  70 /// instead. They are shorter but less discoverable than `as_bytes()`.
  71 ///
  72 /// **Known Problems:** None.
  73 ///
  74 /// **Example:**
  75 /// ```rust
  76 /// let bs = "a byte string".as_bytes();
  77 /// ```
  78 declare_clippy_lint! {
  79     pub STRING_LIT_AS_BYTES,
  80     style,
  81     "calling `as_bytes` on a string literal instead of using a byte string literal"
  82 }
  83
  84 #[derive(Copy, Clone)]
  85 pub struct StringAdd;
  86
  87 impl LintPass for StringAdd {
  88     fn get_lints(&self) -> LintArray {
  89         lint_array!(STRING_ADD, STRING_ADD_ASSIGN)
  90     }
  91 }
  92
  93 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringAdd {
  94     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  95         if let ExprKind::Binary(
  96             Spanned {
  97                 node: BinOpKind::Add, ..
  98             },
  99             ref left,
 100             _,
 101         ) = e.node
 102         {
 103             if is_string(cx, left) {
 104                 if !is_allowed(cx, STRING_ADD_ASSIGN, e.id) {
 105                     let parent = get_parent_expr(cx, e);
 106                     if let Some(p) = parent {
 107                         if let ExprKind::Assign(ref target, _) = p.node {
 108                             // avoid duplicate matches
 109                             if SpanlessEq::new(cx).eq_expr(target, left) {
 110                                 return;
 111                             }
 112                         }
 113                     }
 114                 }
 115                 span_lint(
 116                     cx,
 117                     STRING_ADD,
 118                     e.span,
 119                     "you added something to a string. Consider using `String::push_str()` instead",
 120                 );
 121             }
 122         } else if let ExprKind::Assign(ref target, ref src) = e.node {
 123             if is_string(cx, target) && is_add(cx, src, target) {
 124                 span_lint(
 125                     cx,
 126                     STRING_ADD_ASSIGN,
 127                     e.span,
 128                     "you assigned the result of adding something to this string. Consider using \
 129                      `String::push_str()` instead",
 130                 );
 131             }
 132         }
 133     }
 134 }
 135
 136 fn is_string(cx: &LateContext<'_, '_>, e: &Expr) -> bool {
 137     match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(e)), &paths::STRING)
 138 }
 139
 140 fn is_add(cx: &LateContext<'_, '_>, src: &Expr, target: &Expr) -> bool {
 141     match src.node {
 142         ExprKind::Binary(
 143             Spanned {
 144                 node: BinOpKind::Add, ..
 145             },
 146             ref left,
 147             _,
 148         ) => SpanlessEq::new(cx).eq_expr(target, left),
 149         ExprKind::Block(ref block, _) => {
 150             block.stmts.is_empty() && block.expr.as_ref().map_or(false, |expr| is_add(cx, expr, target))
 151         },
 152         _ => false,
 153     }
 154 }
 155
 156 #[derive(Copy, Clone)]
 157 pub struct StringLitAsBytes;
 158
 159 impl LintPass for StringLitAsBytes {
 160     fn get_lints(&self) -> LintArray {
 161         lint_array!(STRING_LIT_AS_BYTES)
 162     }
 163 }
 164
 165 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StringLitAsBytes {
 166     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
 167         use crate::utils::{in_macro, snippet, snippet_with_applicability};
 168         use syntax::ast::{LitKind, StrStyle};
 169
 170         if let ExprKind::MethodCall(ref path, _, ref args) = e.node {
 171             if path.ident.name == "as_bytes" {
 172                 if let ExprKind::Lit(ref lit) = args[0].node {
 173                     if let LitKind::Str(ref lit_content, style) = lit.node {
 174                         let callsite = snippet(cx, args[0].span.source_callsite(), r#""foo""#);
 175                         let expanded = if let StrStyle::Raw(n) = style {
 176                             let term = (0..n).map(|_| '#').collect::<String>();
 177                             format!("r{0}\"{1}\"{0}", term, lit_content.as_str())
 178                         } else {
 179                             format!("\"{}\"", lit_content.as_str())
 180                         };
 181                         let mut applicability = Applicability::MachineApplicable;
 182                         if callsite.starts_with("include_str!") {
 183                             span_lint_and_sugg(
 184                                 cx,
 185                                 STRING_LIT_AS_BYTES,
 186                                 e.span,
 187                                 "calling `as_bytes()` on `include_str!(..)`",
 188                                 "consider using `include_bytes!(..)` instead",
 189                                 snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability).replacen(
 190                                     "include_str",
 191                                     "include_bytes",
 192                                     1,
 193                                 ),
 194                                 applicability,
 195                             );
 196                         } else if callsite == expanded
 197                             && lit_content.as_str().chars().all(|c| c.is_ascii())
 198                             && !in_macro(args[0].span)
 199                         {
 200                             span_lint_and_sugg(
 201                                 cx,
 202                                 STRING_LIT_AS_BYTES,
 203                                 e.span,
 204                                 "calling `as_bytes()` on a string literal",
 205                                 "consider using a byte string literal instead",
 206                                 format!(
 207                                     "b{}",
 208                                     snippet_with_applicability(cx, args[0].span, r#""foo""#, &mut applicability)
 209                                 ),
 210                                 applicability,
 211                             );
 212                         }
 213                     }
 214                 }
 215             }
 216         }
 217     }
 218 }