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