clippy_lints/src/formatting.rs

   1 use crate::utils::{differing_macro_contexts, in_macro, snippet_opt, span_note_and_lint};
   2 use if_chain::if_chain;
   3 use rustc::lint::{in_external_macro, EarlyContext, EarlyLintPass, LintArray, LintPass};
   4 use rustc::{declare_lint_pass, declare_tool_lint};
   5 use syntax::ast;
   6 use syntax::ptr::P;
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
  10     /// operators.
  11     ///
  12     /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  13     /// confusing.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     /// ```rust,ignore
  19     /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  20     /// ```
  21     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  22     style,
  23     "suspicious formatting of `*=`, `-=` or `!=`"
  24 }
  25
  26 declare_clippy_lint! {
  27     /// **What it does:** Checks for formatting of `else`. It lints if the `else`
  28     /// is followed immediately by a newline or the `else` seems to be missing.
  29     ///
  30     /// **Why is this bad?** This is probably some refactoring remnant, even if the
  31     /// code is correct, it might look confusing.
  32     ///
  33     /// **Known problems:** None.
  34     ///
  35     /// **Example:**
  36     /// ```rust,ignore
  37     /// if foo {
  38     /// } { // looks like an `else` is missing here
  39     /// }
  40     ///
  41     /// if foo {
  42     /// } if bar { // looks like an `else` is missing here
  43     /// }
  44     ///
  45     /// if foo {
  46     /// } else
  47     ///
  48     /// { // this is the `else` block of the previous `if`, but should it be?
  49     /// }
  50     ///
  51     /// if foo {
  52     /// } else
  53     ///
  54     /// if bar { // this is the `else` block of the previous `if`, but should it be?
  55     /// }
  56     /// ```
  57     pub SUSPICIOUS_ELSE_FORMATTING,
  58     style,
  59     "suspicious formatting of `else`"
  60 }
  61
  62 declare_clippy_lint! {
  63     /// **What it does:** Checks for possible missing comma in an array. It lints if
  64     /// an array element is a binary operator expression and it lies on two lines.
  65     ///
  66     /// **Why is this bad?** This could lead to unexpected results.
  67     ///
  68     /// **Known problems:** None.
  69     ///
  70     /// **Example:**
  71     /// ```rust,ignore
  72     /// let a = &[
  73     ///     -1, -2, -3 // <= no comma here
  74     ///     -4, -5, -6
  75     /// ];
  76     /// ```
  77     pub POSSIBLE_MISSING_COMMA,
  78     correctness,
  79     "possible missing comma in array"
  80 }
  81
  82 declare_lint_pass!(Formatting => [
  83     SUSPICIOUS_ASSIGNMENT_FORMATTING,
  84     SUSPICIOUS_ELSE_FORMATTING,
  85     POSSIBLE_MISSING_COMMA
  86 ]);
  87
  88 impl EarlyLintPass for Formatting {
  89     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
  90         for w in block.stmts.windows(2) {
  91             match (&w[0].node, &w[1].node) {
  92                 (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Expr(ref second))
  93                 | (&ast::StmtKind::Expr(ref first), &ast::StmtKind::Semi(ref second)) => {
  94                     check_missing_else(cx, first, second);
  95                 },
  96                 _ => (),
  97             }
  98         }
  99     }
 100
 101     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
 102         check_assign(cx, expr);
 103         check_else(cx, expr);
 104         check_array(cx, expr);
 105     }
 106 }
 107
 108 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 109 fn check_assign(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 110     if let ast::ExprKind::Assign(ref lhs, ref rhs) = expr.node {
 111         if !differing_macro_contexts(lhs.span, rhs.span) && !in_macro(lhs.span) {
 112             let eq_span = lhs.span.between(rhs.span);
 113             if let ast::ExprKind::Unary(op, ref sub_rhs) = rhs.node {
 114                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 115                     let op = ast::UnOp::to_string(op);
 116                     let eqop_span = lhs.span.between(sub_rhs.span);
 117                     if eq_snippet.ends_with('=') {
 118                         span_note_and_lint(
 119                             cx,
 120                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 121                             eqop_span,
 122                             &format!(
 123                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 124                                  really are doing `.. = ({op} ..)`",
 125                                 op = op
 126                             ),
 127                             eqop_span,
 128                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 129                         );
 130                     }
 131                 }
 132             }
 133         }
 134     }
 135 }
 136
 137 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else`.
 138 fn check_else(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 139     if_chain! {
 140         if let Some((then, &Some(ref else_))) = unsugar_if(expr);
 141         if is_block(else_) || unsugar_if(else_).is_some();
 142         if !differing_macro_contexts(then.span, else_.span);
 143         if !in_macro(then.span) && !in_external_macro(cx.sess, expr.span);
 144
 145         // workaround for rust-lang/rust#43081
 146         if expr.span.lo().0 != 0 && expr.span.hi().0 != 0;
 147
 148         // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 149         // the “if” of the “else if” block (excluding)
 150         let else_span = then.span.between(else_.span);
 151
 152         // the snippet should look like " else \n    " with maybe comments anywhere
 153         // it’s bad when there is a ‘\n’ after the “else”
 154         if let Some(else_snippet) = snippet_opt(cx, else_span);
 155         if let Some(else_pos) = else_snippet.find("else");
 156         if else_snippet[else_pos..].contains('\n');
 157         let else_desc = if unsugar_if(else_).is_some() { "if" } else { "{..}" };
 158
 159         then {
 160             span_note_and_lint(
 161                 cx,
 162                 SUSPICIOUS_ELSE_FORMATTING,
 163                 else_span,
 164                 &format!("this is an `else {}` but the formatting might hide it", else_desc),
 165                 else_span,
 166                 &format!(
 167                     "to remove this lint, remove the `else` or remove the new line between \
 168                      `else` and `{}`",
 169                     else_desc,
 170                 ),
 171             );
 172         }
 173     }
 174 }
 175
 176 fn has_unary_equivalent(bin_op: ast::BinOpKind) -> bool {
 177     // &, *, -
 178     bin_op == ast::BinOpKind::And || bin_op == ast::BinOpKind::Mul || bin_op == ast::BinOpKind::Sub
 179 }
 180
 181 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 182 fn check_array(cx: &EarlyContext<'_>, expr: &ast::Expr) {
 183     if let ast::ExprKind::Array(ref array) = expr.node {
 184         for element in array {
 185             if let ast::ExprKind::Binary(ref op, ref lhs, _) = element.node {
 186                 if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span) {
 187                     let space_span = lhs.span.between(op.span);
 188                     if let Some(space_snippet) = snippet_opt(cx, space_span) {
 189                         let lint_span = lhs.span.with_lo(lhs.span.hi());
 190                         if space_snippet.contains('\n') {
 191                             span_note_and_lint(
 192                                 cx,
 193                                 POSSIBLE_MISSING_COMMA,
 194                                 lint_span,
 195                                 "possibly missing a comma here",
 196                                 lint_span,
 197                                 "to remove this lint, add a comma or write the expr in a single line",
 198                             );
 199                         }
 200                     }
 201                 }
 202             }
 203         }
 204     }
 205 }
 206
 207 fn check_missing_else(cx: &EarlyContext<'_>, first: &ast::Expr, second: &ast::Expr) {
 208     if !differing_macro_contexts(first.span, second.span)
 209         && !in_macro(first.span)
 210         && unsugar_if(first).is_some()
 211         && (is_block(second) || unsugar_if(second).is_some())
 212     {
 213         // where the else would be
 214         let else_span = first.span.between(second.span);
 215
 216         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 217             if !else_snippet.contains('\n') {
 218                 let (looks_like, next_thing) = if unsugar_if(second).is_some() {
 219                     ("an `else if`", "the second `if`")
 220                 } else {
 221                     ("an `else {..}`", "the next block")
 222                 };
 223
 224                 span_note_and_lint(
 225                     cx,
 226                     SUSPICIOUS_ELSE_FORMATTING,
 227                     else_span,
 228                     &format!("this looks like {} but the `else` is missing", looks_like),
 229                     else_span,
 230                     &format!(
 231                         "to remove this lint, add the missing `else` or add a new line before {}",
 232                         next_thing,
 233                     ),
 234                 );
 235             }
 236         }
 237     }
 238 }
 239
 240 fn is_block(expr: &ast::Expr) -> bool {
 241     if let ast::ExprKind::Block(..) = expr.node {
 242         true
 243     } else {
 244         false
 245     }
 246 }
 247
 248 /// Match `if` or `if let` expressions and return the `then` and `else` block.
 249 fn unsugar_if(expr: &ast::Expr) -> Option<(&P<ast::Block>, &Option<P<ast::Expr>>)> {
 250     match expr.node {
 251         ast::ExprKind::If(_, ref then, ref else_) | ast::ExprKind::IfLet(_, _, ref then, ref else_) => {
 252             Some((then, else_))
 253         },
 254         _ => None,
 255     }
 256 }