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
  11 use crate::rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use crate::syntax::ast;
  14 use crate::utils::{differing_macro_contexts, in_macro, snippet_opt, span_note_and_lint};
  15 use crate::syntax::ptr::P;
  16
  17 /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
  18 /// operators.
  19 ///
  20 /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  21 /// confusing.
  22 ///
  23 /// **Known problems:** None.
  24 ///
  25 /// **Example:**
  26 /// ```rust,ignore
  27 /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  28 /// ```
  29 declare_clippy_lint! {
  30     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  31     style,
  32     "suspicious formatting of `*=`, `-=` or `!=`"
  33 }
  34
  35 /// **What it does:** Checks for formatting of `else if`. It lints if the `else`
  36 /// and `if` are not on the same line or the `else` seems to be missing.
  37 ///
  38 /// **Why is this bad?** This is probably some refactoring remnant, even if the
  39 /// code is correct, it might look confusing.
  40 ///
  41 /// **Known problems:** None.
  42 ///
  43 /// **Example:**
  44 /// ```rust,ignore
  45 /// if foo {
  46 /// } if bar { // looks like an `else` is missing here
  47 /// }
  48 ///
  49 /// if foo {
  50 /// } else
  51 ///
  52 /// if bar { // this is the `else` block of the previous `if`, but should it be?
  53 /// }
  54 /// ```
  55 declare_clippy_lint! {
  56     pub SUSPICIOUS_ELSE_FORMATTING,
  57     style,
  58     "suspicious formatting of `else if`"
  59 }
  60
  61 /// **What it does:** Checks for possible missing comma in an array. It lints if
  62 /// an array element is a binary operator expression and it lies on two lines.
  63 ///
  64 /// **Why is this bad?** This could lead to unexpected results.
  65 ///
  66 /// **Known problems:** None.
  67 ///
  68 /// **Example:**
  69 /// ```rust,ignore
  70 /// let a = &[
  71 ///     -1, -2, -3 // <= no comma here
  72 ///     -4, -5, -6
  73 /// ];
  74 /// ```
  75 declare_clippy_lint! {
  76     pub POSSIBLE_MISSING_COMMA,
  77     correctness,
  78     "possible missing comma in array"
  79 }
  80
  81
  82 #[derive(Copy, Clone)]
  83 pub struct Formatting;
  84
  85 impl LintPass for Formatting {
  86     fn get_lints(&self) -> LintArray {
  87         lint_array!(
  88             SUSPICIOUS_ASSIGNMENT_FORMATTING,
  89             SUSPICIOUS_ELSE_FORMATTING,
  90             POSSIBLE_MISSING_COMMA
  91         )
  92     }
  93 }
  94
  95 impl EarlyLintPass for Formatting {
  96     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
  97         for w in block.stmts.windows(2) {
  98             match (&w[0].node, &w[1].node) {
  99                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Expr(ref second)) |
 100                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Semi(ref second)) => {
 101                     check_consecutive_ifs(cx, first, second);
 102                 },
 103                 _ => (),
 104             }
 105         }
 106     }
 107
 108     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 109         check_assign(cx, expr);
 110         check_else_if(cx, expr);
 111         check_array(cx, expr);
 112     }
 113 }
 114
 115 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 116 fn check_assign(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 117     if let ast::ExprKind::Assign(ref lhs, ref rhs) = expr.node {
 118         if !differing_macro_contexts(lhs.span, rhs.span) && !in_macro(lhs.span) {
 119             let eq_span = lhs.span.between(rhs.span);
 120             if let ast::ExprKind::Unary(op, ref sub_rhs) = rhs.node {
 121                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 122                     let op = ast::UnOp::to_string(op);
 123                     let eqop_span = lhs.span.between(sub_rhs.span);
 124                     if eq_snippet.ends_with('=') {
 125                         span_note_and_lint(
 126                             cx,
 127                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 128                             eqop_span,
 129                             &format!(
 130                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 131                                  really are doing `.. = ({op} ..)`",
 132                                 op = op
 133                             ),
 134                             eqop_span,
 135                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 136                         );
 137                     }
 138                 }
 139             }
 140         }
 141     }
 142 }
 143
 144 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else if`.
 145 fn check_else_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 146     if let Some((then, &Some(ref else_))) = unsugar_if(expr) {
 147         if unsugar_if(else_).is_some() && !differing_macro_contexts(then.span, else_.span) && !in_macro(then.span) {
 148             // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 149             // the
 150             // “if” of the “else if” block (excluding)
 151             let else_span = then.span.between(else_.span);
 152
 153             // the snippet should look like " else \n    " with maybe comments anywhere
 154             // it’s bad when there is a ‘\n’ after the “else”
 155             if let Some(else_snippet) = snippet_opt(cx, else_span) {
 156                 let else_pos = else_snippet
 157                     .find("else")
 158                     .expect("there must be a `else` here");
 159
 160                 if else_snippet[else_pos..].contains('\n') {
 161                     span_note_and_lint(
 162                         cx,
 163                         SUSPICIOUS_ELSE_FORMATTING,
 164                         else_span,
 165                         "this is an `else if` but the formatting might hide it",
 166                         else_span,
 167                         "to remove this lint, remove the `else` or remove the new line between `else` \
 168                          and `if`",
 169                     );
 170                 }
 171             }
 172         }
 173     }
 174 }
 175
 176 fn has_unary_equivalent(bin_op: ast::BinOpKind) -> bool {
 177     //+, &, *, -
 178     bin_op == ast::BinOpKind::Add
 179     || bin_op == ast::BinOpKind::And
 180     || bin_op == ast::BinOpKind::Mul
 181     || bin_op == ast::BinOpKind::Sub
 182 }
 183
 184 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 185 fn check_array(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 186     if let ast::ExprKind::Array(ref array) = expr.node {
 187         for element in array {
 188             if let ast::ExprKind::Binary(ref op, ref lhs, _) = element.node {
 189                 if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span) {
 190                     let space_span = lhs.span.between(op.span);
 191                     if let Some(space_snippet) = snippet_opt(cx, space_span) {
 192                         let lint_span = lhs.span.with_lo(lhs.span.hi());
 193                         if space_snippet.contains('\n') {
 194                             span_note_and_lint(
 195                                 cx,
 196                                 POSSIBLE_MISSING_COMMA,
 197                                 lint_span,
 198                                 "possibly missing a comma here",
 199                                 lint_span,
 200                                 "to remove this lint, add a comma or write the expr in a single line",
 201                             );
 202                         }
 203                     }
 204                 }
 205             }
 206         }
 207     }
 208 }
 209
 210 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for consecutive ifs.
 211 fn check_consecutive_ifs(cx: &EarlyContext<'_>, first: &ast::Expr, second: &ast::Expr) {
 212     if !differing_macro_contexts(first.span, second.span) && !in_macro(first.span) && unsugar_if(first).is_some()
 213         && unsugar_if(second).is_some()
 214     {
 215         // where the else would be
 216         let else_span = first.span.between(second.span);
 217
 218         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 219             if !else_snippet.contains('\n') {
 220                 span_note_and_lint(
 221                     cx,
 222                     SUSPICIOUS_ELSE_FORMATTING,
 223                     else_span,
 224                     "this looks like an `else if` but the `else` is missing",
 225                     else_span,
 226                     "to remove this lint, add the missing `else` or add a new line before the second \
 227                      `if`",
 228                 );
 229             }
 230         }
 231     }
 232 }
 233
 234 /// Match `if` or `if let` expressions and return the `then` and `else` block.
 235 fn unsugar_if(expr: &ast::Expr) -> Option<(&P<ast::Block>, &Option<P<ast::Expr>>)> {
 236     match expr.node {
 237         ast::ExprKind::If(_, ref then, ref else_) | ast::ExprKind::IfLet(_, _, ref then, ref else_) => {
 238             Some((then, else_))
 239         },
 240         _ => None,
 241     }
 242 }