clippy_lints/src/formatting.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::{differing_macro_contexts, in_macro, snippet_opt, span_note_and_lint};
  11 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
  12 use rustc::{declare_tool_lint, lint_array};
  13 use syntax::ast;
  14 use syntax::ptr::P;
  15
  16 /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
  17 /// operators.
  18 ///
  19 /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  20 /// confusing.
  21 ///
  22 /// **Known problems:** None.
  23 ///
  24 /// **Example:**
  25 /// ```rust,ignore
  26 /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  27 /// ```
  28 declare_clippy_lint! {
  29     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  30     style,
  31     "suspicious formatting of `*=`, `-=` or `!=`"
  32 }
  33
  34 /// **What it does:** Checks for formatting of `else`. It lints if the `else`
  35 /// is followed immediately by a newline or the `else` seems to be missing.
  36 ///
  37 /// **Why is this bad?** This is probably some refactoring remnant, even if the
  38 /// code is correct, it might look confusing.
  39 ///
  40 /// **Known problems:** None.
  41 ///
  42 /// **Example:**
  43 /// ```rust,ignore
  44 /// if foo {
  45 /// } { // looks like an `else` is missing here
  46 /// }
  47 ///
  48 /// if foo {
  49 /// } if bar { // looks like an `else` is missing here
  50 /// }
  51 ///
  52 /// if foo {
  53 /// } else
  54 ///
  55 /// { // this is the `else` block of the previous `if`, but should it be?
  56 /// }
  57 ///
  58 /// if foo {
  59 /// } else
  60 ///
  61 /// if bar { // this is the `else` block of the previous `if`, but should it be?
  62 /// }
  63 /// ```
  64 declare_clippy_lint! {
  65     pub SUSPICIOUS_ELSE_FORMATTING,
  66     style,
  67     "suspicious formatting of `else`"
  68 }
  69
  70 /// **What it does:** Checks for possible missing comma in an array. It lints if
  71 /// an array element is a binary operator expression and it lies on two lines.
  72 ///
  73 /// **Why is this bad?** This could lead to unexpected results.
  74 ///
  75 /// **Known problems:** None.
  76 ///
  77 /// **Example:**
  78 /// ```rust,ignore
  79 /// let a = &[
  80 ///     -1, -2, -3 // <= no comma here
  81 ///     -4, -5, -6
  82 /// ];
  83 /// ```
  84 declare_clippy_lint! {
  85     pub POSSIBLE_MISSING_COMMA,
  86     correctness,
  87     "possible missing comma in array"
  88 }
  89
  90 #[derive(Copy, Clone)]
  91 pub struct Formatting;
  92
  93 impl LintPass for Formatting {
  94     fn get_lints(&self) -> LintArray {
  95         lint_array!(
  96             SUSPICIOUS_ASSIGNMENT_FORMATTING,
  97             SUSPICIOUS_ELSE_FORMATTING,
  98             POSSIBLE_MISSING_COMMA
  99         )
 100     }
 101 }
 102
 103 impl EarlyLintPass for Formatting {
 104     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
 105         for w in block.stmts.windows(2) {
 106             match (&w[0].node, &w[1].node) {
 107                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Expr(ref second))
 108                 | (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Semi(ref second)) => {
 109                     check_missing_else(cx, first, second);
 110                 },
 111                 _ => (),
 112             }
 113         }
 114     }
 115
 116     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 117         check_assign(cx, expr);
 118         check_else(cx, expr);
 119         check_array(cx, expr);
 120     }
 121 }
 122
 123 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 124 fn check_assign(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 125     if let ast::ExprKind::Assign(ref lhs, ref rhs) = expr.node {
 126         if !differing_macro_contexts(lhs.span, rhs.span) && !in_macro(lhs.span) {
 127             let eq_span = lhs.span.between(rhs.span);
 128             if let ast::ExprKind::Unary(op, ref sub_rhs) = rhs.node {
 129                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 130                     let op = ast::UnOp::to_string(op);
 131                     let eqop_span = lhs.span.between(sub_rhs.span);
 132                     if eq_snippet.ends_with('=') {
 133                         span_note_and_lint(
 134                             cx,
 135                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 136                             eqop_span,
 137                             &format!(
 138                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 139                                  really are doing `.. = ({op} ..)`",
 140                                 op = op
 141                             ),
 142                             eqop_span,
 143                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 144                         );
 145                     }
 146                 }
 147             }
 148         }
 149     }
 150 }
 151
 152 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else`.
 153 fn check_else(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 154     if let Some((then, &Some(ref else_))) = unsugar_if(expr) {
 155         if (is_block(else_) || unsugar_if(else_).is_some())
 156             && !differing_macro_contexts(then.span, else_.span)
 157             && !in_macro(then.span)
 158         {
 159             // workaround for rust-lang/rust#43081
 160             if expr.span.lo().0 == 0 && expr.span.hi().0 == 0 {
 161                 return;
 162             }
 163
 164             // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 165             // the
 166             // “if” of the “else if” block (excluding)
 167             let else_span = then.span.between(else_.span);
 168
 169             // the snippet should look like " else \n    " with maybe comments anywhere
 170             // it’s bad when there is a ‘\n’ after the “else”
 171             if let Some(else_snippet) = snippet_opt(cx, else_span) {
 172                 let else_pos = else_snippet.find("else").expect("there must be a `else` here");
 173
 174                 if else_snippet[else_pos..].contains('\n') {
 175                     let else_desc = if unsugar_if(else_).is_some() { "if" } else { "{..}" };
 176
 177                     span_note_and_lint(
 178                         cx,
 179                         SUSPICIOUS_ELSE_FORMATTING,
 180                         else_span,
 181                         &format!("this is an `else {}` but the formatting might hide it", else_desc),
 182                         else_span,
 183                         &format!(
 184                             "to remove this lint, remove the `else` or remove the new line between \
 185                              `else` and `{}`",
 186                             else_desc,
 187                         ),
 188                     );
 189                 }
 190             }
 191         }
 192     }
 193 }
 194
 195 fn has_unary_equivalent(bin_op: ast::BinOpKind) -> bool {
 196     // &, *, -
 197     bin_op == ast::BinOpKind::And || bin_op == ast::BinOpKind::Mul || bin_op == ast::BinOpKind::Sub
 198 }
 199
 200 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 201 fn check_array(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 202     if let ast::ExprKind::Array(ref array) = expr.node {
 203         for element in array {
 204             if let ast::ExprKind::Binary(ref op, ref lhs, _) = element.node {
 205                 if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span) {
 206                     let space_span = lhs.span.between(op.span);
 207                     if let Some(space_snippet) = snippet_opt(cx, space_span) {
 208                         let lint_span = lhs.span.with_lo(lhs.span.hi());
 209                         if space_snippet.contains('\n') {
 210                             span_note_and_lint(
 211                                 cx,
 212                                 POSSIBLE_MISSING_COMMA,
 213                                 lint_span,
 214                                 "possibly missing a comma here",
 215                                 lint_span,
 216                                 "to remove this lint, add a comma or write the expr in a single line",
 217                             );
 218                         }
 219                     }
 220                 }
 221             }
 222         }
 223     }
 224 }
 225
 226 fn check_missing_else(cx: &EarlyContext<'_>, first: &ast::Expr, second: &ast::Expr) {
 227     if !differing_macro_contexts(first.span, second.span)
 228         && !in_macro(first.span)
 229         && unsugar_if(first).is_some()
 230         && (is_block(second) || unsugar_if(second).is_some())
 231     {
 232         // where the else would be
 233         let else_span = first.span.between(second.span);
 234
 235         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 236             if !else_snippet.contains('\n') {
 237                 let (looks_like, next_thing) = if unsugar_if(second).is_some() {
 238                     ("an `else if`", "the second `if`")
 239                 } else {
 240                     ("an `else {..}`", "the next block")
 241                 };
 242
 243                 span_note_and_lint(
 244                     cx,
 245                     SUSPICIOUS_ELSE_FORMATTING,
 246                     else_span,
 247                     &format!("this looks like {} but the `else` is missing", looks_like),
 248                     else_span,
 249                     &format!(
 250                         "to remove this lint, add the missing `else` or add a new line before {}",
 251                         next_thing,
 252                     ),
 253                 );
 254             }
 255         }
 256     }
 257 }
 258
 259 fn is_block(expr: &ast::Expr) -> bool {
 260     if let ast::ExprKind::Block(..) = expr.node {
 261         true
 262     } else {
 263         false
 264     }
 265 }
 266
 267 /// Match `if` or `if let` expressions and return the `then` and `else` block.
 268 fn unsugar_if(expr: &ast::Expr) -> Option<(&P<ast::Block>, &Option<P<ast::Expr>>)> {
 269     match expr.node {
 270         ast::ExprKind::If(_, ref then, ref else_) | ast::ExprKind::IfLet(_, _, ref then, ref else_) => {
 271             Some((then, else_))
 272         },
 273         _ => None,
 274     }
 275 }