clippy_lints/src/formatting.rs

   1 use rustc::lint::*;
   2 use rustc::{declare_lint, lint_array};
   3 use syntax::ast;
   4 use crate::utils::{differing_macro_contexts, in_macro, snippet_opt, span_note_and_lint};
   5 use syntax::ptr::P;
   6
   7 /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
   8 /// operators.
   9 ///
  10 /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  11 /// confusing.
  12 ///
  13 /// **Known problems:** None.
  14 ///
  15 /// **Example:**
  16 /// ```rust,ignore
  17 /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  18 /// ```
  19 declare_clippy_lint! {
  20     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  21     style,
  22     "suspicious formatting of `*=`, `-=` or `!=`"
  23 }
  24
  25 /// **What it does:** Checks for formatting of `else if`. It lints if the `else`
  26 /// and `if` are not on the same line or the `else` seems to be missing.
  27 ///
  28 /// **Why is this bad?** This is probably some refactoring remnant, even if the
  29 /// code is correct, it might look confusing.
  30 ///
  31 /// **Known problems:** None.
  32 ///
  33 /// **Example:**
  34 /// ```rust,ignore
  35 /// if foo {
  36 /// } if bar { // looks like an `else` is missing here
  37 /// }
  38 ///
  39 /// if foo {
  40 /// } else
  41 ///
  42 /// if bar { // this is the `else` block of the previous `if`, but should it be?
  43 /// }
  44 /// ```
  45 declare_clippy_lint! {
  46     pub SUSPICIOUS_ELSE_FORMATTING,
  47     style,
  48     "suspicious formatting of `else if`"
  49 }
  50
  51 /// **What it does:** Checks for possible missing comma in an array. It lints if
  52 /// an array element is a binary operator expression and it lies on two lines.
  53 ///
  54 /// **Why is this bad?** This could lead to unexpected results.
  55 ///
  56 /// **Known problems:** None.
  57 ///
  58 /// **Example:**
  59 /// ```rust,ignore
  60 /// let a = &[
  61 ///     -1, -2, -3 // <= no comma here
  62 ///     -4, -5, -6
  63 /// ];
  64 /// ```
  65 declare_clippy_lint! {
  66     pub POSSIBLE_MISSING_COMMA,
  67     correctness,
  68     "possible missing comma in array"
  69 }
  70
  71
  72 #[derive(Copy, Clone)]
  73 pub struct Formatting;
  74
  75 impl LintPass for Formatting {
  76     fn get_lints(&self) -> LintArray {
  77         lint_array!(
  78             SUSPICIOUS_ASSIGNMENT_FORMATTING,
  79             SUSPICIOUS_ELSE_FORMATTING,
  80             POSSIBLE_MISSING_COMMA
  81         )
  82     }
  83 }
  84
  85 impl EarlyLintPass for Formatting {
  86     fn check_block(&mut self, cx: &EarlyContext, block: &ast::Block) {
  87         for w in block.stmts.windows(2) {
  88             match (&w[0].node, &w[1].node) {
  89                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Expr(ref second)) |
  90                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Semi(ref second)) => {
  91                     check_consecutive_ifs(cx, first, second);
  92                 },
  93                 _ => (),
  94             }
  95         }
  96     }
  97
  98     fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
  99         check_assign(cx, expr);
 100         check_else_if(cx, expr);
 101         check_array(cx, expr);
 102     }
 103 }
 104
 105 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 106 fn check_assign(cx: &EarlyContext, expr: &ast::Expr) {
 107     if let ast::ExprKind::Assign(ref lhs, ref rhs) = expr.node {
 108         if !differing_macro_contexts(lhs.span, rhs.span) && !in_macro(lhs.span) {
 109             let eq_span = lhs.span.between(rhs.span);
 110             if let ast::ExprKind::Unary(op, ref sub_rhs) = rhs.node {
 111                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 112                     let op = ast::UnOp::to_string(op);
 113                     let eqop_span = lhs.span.between(sub_rhs.span);
 114                     if eq_snippet.ends_with('=') {
 115                         span_note_and_lint(
 116                             cx,
 117                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 118                             eqop_span,
 119                             &format!(
 120                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 121                                  really are doing `.. = ({op} ..)`",
 122                                 op = op
 123                             ),
 124                             eqop_span,
 125                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 126                         );
 127                     }
 128                 }
 129             }
 130         }
 131     }
 132 }
 133
 134 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else if`.
 135 fn check_else_if(cx: &EarlyContext, expr: &ast::Expr) {
 136     if let Some((then, &Some(ref else_))) = unsugar_if(expr) {
 137         if unsugar_if(else_).is_some() && !differing_macro_contexts(then.span, else_.span) && !in_macro(then.span) {
 138             // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 139             // the
 140             // “if” of the “else if” block (excluding)
 141             let else_span = then.span.between(else_.span);
 142
 143             // the snippet should look like " else \n    " with maybe comments anywhere
 144             // it’s bad when there is a ‘\n’ after the “else”
 145             if let Some(else_snippet) = snippet_opt(cx, else_span) {
 146                 let else_pos = else_snippet
 147                     .find("else")
 148                     .expect("there must be a `else` here");
 149
 150                 if else_snippet[else_pos..].contains('\n') {
 151                     span_note_and_lint(
 152                         cx,
 153                         SUSPICIOUS_ELSE_FORMATTING,
 154                         else_span,
 155                         "this is an `else if` but the formatting might hide it",
 156                         else_span,
 157                         "to remove this lint, remove the `else` or remove the new line between `else` \
 158                          and `if`",
 159                     );
 160                 }
 161             }
 162         }
 163     }
 164 }
 165
 166 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 167 fn check_array(cx: &EarlyContext, expr: &ast::Expr) {
 168     if let ast::ExprKind::Array(ref array) = expr.node {
 169         for element in array {
 170             if let ast::ExprKind::Binary(ref op, ref lhs, _) = element.node {
 171                 if !differing_macro_contexts(lhs.span, op.span) {
 172                     let space_span = lhs.span.between(op.span);
 173                     if let Some(space_snippet) = snippet_opt(cx, space_span) {
 174                         let lint_span = lhs.span.with_lo(lhs.span.hi());
 175                         if space_snippet.contains('\n') {
 176                             span_note_and_lint(
 177                                 cx,
 178                                 POSSIBLE_MISSING_COMMA,
 179                                 lint_span,
 180                                 "possibly missing a comma here",
 181                                 lint_span,
 182                                 "to remove this lint, add a comma or write the expr in a single line",
 183                             );
 184                         }
 185                     }
 186                 }
 187             }
 188         }
 189     }
 190 }
 191
 192 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for consecutive ifs.
 193 fn check_consecutive_ifs(cx: &EarlyContext, first: &ast::Expr, second: &ast::Expr) {
 194     if !differing_macro_contexts(first.span, second.span) && !in_macro(first.span) && unsugar_if(first).is_some()
 195         && unsugar_if(second).is_some()
 196     {
 197         // where the else would be
 198         let else_span = first.span.between(second.span);
 199
 200         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 201             if !else_snippet.contains('\n') {
 202                 span_note_and_lint(
 203                     cx,
 204                     SUSPICIOUS_ELSE_FORMATTING,
 205                     else_span,
 206                     "this looks like an `else if` but the `else` is missing",
 207                     else_span,
 208                     "to remove this lint, add the missing `else` or add a new line before the second \
 209                      `if`",
 210                 );
 211             }
 212         }
 213     }
 214 }
 215
 216 /// Match `if` or `if let` expressions and return the `then` and `else` block.
 217 fn unsugar_if(expr: &ast::Expr) -> Option<(&P<ast::Block>, &Option<P<ast::Expr>>)> {
 218     match expr.node {
 219         ast::ExprKind::If(_, ref then, ref else_) | ast::ExprKind::IfLet(_, _, ref then, ref else_) => {
 220             Some((then, else_))
 221         },
 222         _ => None,
 223     }
 224 }