clippy_lints/src/formatting.rs

   1 use crate::utils::{differing_macro_contexts, snippet_opt, span_lint_and_help, span_lint_and_note};
   2 use if_chain::if_chain;
   3 use rustc_ast::ast::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
   4 use rustc_lint::{EarlyContext, EarlyLintPass};
   5 use rustc_middle::lint::in_external_macro;
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::source_map::Span;
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
  11     /// operators.
  12     ///
  13     /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  14     /// confusing.
  15     ///
  16     /// **Known problems:** None.
  17     ///
  18     /// **Example:**
  19     /// ```rust,ignore
  20     /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  21     /// ```
  22     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  23     style,
  24     "suspicious formatting of `*=`, `-=` or `!=`"
  25 }
  26
  27 declare_clippy_lint! {
  28     /// **What it does:** Checks the formatting of a unary operator on the right hand side
  29     /// of a binary operator. It lints if there is no space between the binary and unary operators,
  30     /// but there is a space between the unary and its operand.
  31     ///
  32     /// **Why is this bad?** This is either a typo in the binary operator or confusing.
  33     ///
  34     /// **Known problems:** None.
  35     ///
  36     /// **Example:**
  37     /// ```rust,ignore
  38     /// if foo <- 30 { // this should be `foo < -30` but looks like a different operator
  39     /// }
  40     ///
  41     /// if foo &&! bar { // this should be `foo && !bar` but looks like a different operator
  42     /// }
  43     /// ```
  44     pub SUSPICIOUS_UNARY_OP_FORMATTING,
  45     style,
  46     "suspicious formatting of unary `-` or `!` on the RHS of a BinOp"
  47 }
  48
  49 declare_clippy_lint! {
  50     /// **What it does:** Checks for formatting of `else`. It lints if the `else`
  51     /// is followed immediately by a newline or the `else` seems to be missing.
  52     ///
  53     /// **Why is this bad?** This is probably some refactoring remnant, even if the
  54     /// code is correct, it might look confusing.
  55     ///
  56     /// **Known problems:** None.
  57     ///
  58     /// **Example:**
  59     /// ```rust,ignore
  60     /// if foo {
  61     /// } { // looks like an `else` is missing here
  62     /// }
  63     ///
  64     /// if foo {
  65     /// } if bar { // looks like an `else` is missing here
  66     /// }
  67     ///
  68     /// if foo {
  69     /// } else
  70     ///
  71     /// { // this is the `else` block of the previous `if`, but should it be?
  72     /// }
  73     ///
  74     /// if foo {
  75     /// } else
  76     ///
  77     /// if bar { // this is the `else` block of the previous `if`, but should it be?
  78     /// }
  79     /// ```
  80     pub SUSPICIOUS_ELSE_FORMATTING,
  81     style,
  82     "suspicious formatting of `else`"
  83 }
  84
  85 declare_clippy_lint! {
  86     /// **What it does:** Checks for possible missing comma in an array. It lints if
  87     /// an array element is a binary operator expression and it lies on two lines.
  88     ///
  89     /// **Why is this bad?** This could lead to unexpected results.
  90     ///
  91     /// **Known problems:** None.
  92     ///
  93     /// **Example:**
  94     /// ```rust,ignore
  95     /// let a = &[
  96     ///     -1, -2, -3 // <= no comma here
  97     ///     -4, -5, -6
  98     /// ];
  99     /// ```
 100     pub POSSIBLE_MISSING_COMMA,
 101     correctness,
 102     "possible missing comma in array"
 103 }
 104
 105 declare_lint_pass!(Formatting => [
 106     SUSPICIOUS_ASSIGNMENT_FORMATTING,
 107     SUSPICIOUS_UNARY_OP_FORMATTING,
 108     SUSPICIOUS_ELSE_FORMATTING,
 109     POSSIBLE_MISSING_COMMA
 110 ]);
 111
 112 impl EarlyLintPass for Formatting {
 113     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 114         for w in block.stmts.windows(2) {
 115             match (&w[0].kind, &w[1].kind) {
 116                 (&StmtKind::Expr(ref first), &StmtKind::Expr(ref second))
 117                 | (&StmtKind::Expr(ref first), &StmtKind::Semi(ref second)) => {
 118                     check_missing_else(cx, first, second);
 119                 },
 120                 _ => (),
 121             }
 122         }
 123     }
 124
 125     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 126         check_assign(cx, expr);
 127         check_unop(cx, expr);
 128         check_else(cx, expr);
 129         check_array(cx, expr);
 130     }
 131 }
 132
 133 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 134 fn check_assign(cx: &EarlyContext<'_>, expr: &Expr) {
 135     if let ExprKind::Assign(ref lhs, ref rhs, _) = expr.kind {
 136         if !differing_macro_contexts(lhs.span, rhs.span) && !lhs.span.from_expansion() {
 137             let eq_span = lhs.span.between(rhs.span);
 138             if let ExprKind::Unary(op, ref sub_rhs) = rhs.kind {
 139                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 140                     let op = UnOp::to_string(op);
 141                     let eqop_span = lhs.span.between(sub_rhs.span);
 142                     if eq_snippet.ends_with('=') {
 143                         span_lint_and_note(
 144                             cx,
 145                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 146                             eqop_span,
 147                             &format!(
 148                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 149                                  really are doing `.. = ({op} ..)`",
 150                                 op = op
 151                             ),
 152                             eqop_span,
 153                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 154                         );
 155                     }
 156                 }
 157             }
 158         }
 159     }
 160 }
 161
 162 /// Implementation of the `SUSPICIOUS_UNARY_OP_FORMATTING` lint.
 163 fn check_unop(cx: &EarlyContext<'_>, expr: &Expr) {
 164     if_chain! {
 165         if let ExprKind::Binary(ref binop, ref lhs, ref rhs) = expr.kind;
 166         if !differing_macro_contexts(lhs.span, rhs.span) && !lhs.span.from_expansion();
 167         // span between BinOp LHS and RHS
 168         let binop_span = lhs.span.between(rhs.span);
 169         // if RHS is a UnOp
 170         if let ExprKind::Unary(op, ref un_rhs) = rhs.kind;
 171         // from UnOp operator to UnOp operand
 172         let unop_operand_span = rhs.span.until(un_rhs.span);
 173         if let Some(binop_snippet) = snippet_opt(cx, binop_span);
 174         if let Some(unop_operand_snippet) = snippet_opt(cx, unop_operand_span);
 175         let binop_str = BinOpKind::to_string(&binop.node);
 176         // no space after BinOp operator and space after UnOp operator
 177         if binop_snippet.ends_with(binop_str) && unop_operand_snippet.ends_with(' ');
 178         then {
 179             let unop_str = UnOp::to_string(op);
 180             let eqop_span = lhs.span.between(un_rhs.span);
 181             span_lint_and_help(
 182                 cx,
 183                 SUSPICIOUS_UNARY_OP_FORMATTING,
 184                 eqop_span,
 185                 &format!(
 186                     "by not having a space between `{binop}` and `{unop}` it looks like \
 187                      `{binop}{unop}` is a single operator",
 188                     binop = binop_str,
 189                     unop = unop_str
 190                 ),
 191                 &format!(
 192                     "put a space between `{binop}` and `{unop}` and remove the space after `{unop}`",
 193                     binop = binop_str,
 194                     unop = unop_str
 195                 ),
 196             );
 197         }
 198     }
 199 }
 200
 201 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else`.
 202 fn check_else(cx: &EarlyContext<'_>, expr: &Expr) {
 203     if_chain! {
 204         if let ExprKind::If(_, then, Some(else_)) = &expr.kind;
 205         if is_block(else_) || is_if(else_);
 206         if !differing_macro_contexts(then.span, else_.span);
 207         if !then.span.from_expansion() && !in_external_macro(cx.sess, expr.span);
 208
 209         // workaround for rust-lang/rust#43081
 210         if expr.span.lo().0 != 0 && expr.span.hi().0 != 0;
 211
 212         // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 213         // the “if” of the “else if” block (excluding)
 214         let else_span = then.span.between(else_.span);
 215
 216         // the snippet should look like " else \n    " with maybe comments anywhere
 217         // it’s bad when there is a ‘\n’ after the “else”
 218         if let Some(else_snippet) = snippet_opt(cx, else_span);
 219         if let Some(else_pos) = else_snippet.find("else");
 220         if else_snippet[else_pos..].contains('\n');
 221         let else_desc = if is_if(else_) { "if" } else { "{..}" };
 222
 223         then {
 224             span_lint_and_note(
 225                 cx,
 226                 SUSPICIOUS_ELSE_FORMATTING,
 227                 else_span,
 228                 &format!("this is an `else {}` but the formatting might hide it", else_desc),
 229                 else_span,
 230                 &format!(
 231                     "to remove this lint, remove the `else` or remove the new line between \
 232                      `else` and `{}`",
 233                     else_desc,
 234                 ),
 235             );
 236         }
 237     }
 238 }
 239
 240 #[must_use]
 241 fn has_unary_equivalent(bin_op: BinOpKind) -> bool {
 242     // &, *, -
 243     bin_op == BinOpKind::And || bin_op == BinOpKind::Mul || bin_op == BinOpKind::Sub
 244 }
 245
 246 fn indentation(cx: &EarlyContext<'_>, span: Span) -> usize {
 247     cx.sess.source_map().lookup_char_pos(span.lo()).col.0
 248 }
 249
 250 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 251 fn check_array(cx: &EarlyContext<'_>, expr: &Expr) {
 252     if let ExprKind::Array(ref array) = expr.kind {
 253         for element in array {
 254             if_chain! {
 255                 if let ExprKind::Binary(ref op, ref lhs, _) = element.kind;
 256                 if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span);
 257                 let space_span = lhs.span.between(op.span);
 258                 if let Some(space_snippet) = snippet_opt(cx, space_span);
 259                 let lint_span = lhs.span.with_lo(lhs.span.hi());
 260                 if space_snippet.contains('\n');
 261                 if indentation(cx, op.span) <= indentation(cx, lhs.span);
 262                 then {
 263                     span_lint_and_note(
 264                         cx,
 265                         POSSIBLE_MISSING_COMMA,
 266                         lint_span,
 267                         "possibly missing a comma here",
 268                         lint_span,
 269                         "to remove this lint, add a comma or write the expr in a single line",
 270                     );
 271                 }
 272             }
 273         }
 274     }
 275 }
 276
 277 fn check_missing_else(cx: &EarlyContext<'_>, first: &Expr, second: &Expr) {
 278     if !differing_macro_contexts(first.span, second.span)
 279         && !first.span.from_expansion()
 280         && is_if(first)
 281         && (is_block(second) || is_if(second))
 282     {
 283         // where the else would be
 284         let else_span = first.span.between(second.span);
 285
 286         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 287             if !else_snippet.contains('\n') {
 288                 let (looks_like, next_thing) = if is_if(second) {
 289                     ("an `else if`", "the second `if`")
 290                 } else {
 291                     ("an `else {..}`", "the next block")
 292                 };
 293
 294                 span_lint_and_note(
 295                     cx,
 296                     SUSPICIOUS_ELSE_FORMATTING,
 297                     else_span,
 298                     &format!("this looks like {} but the `else` is missing", looks_like),
 299                     else_span,
 300                     &format!(
 301                         "to remove this lint, add the missing `else` or add a new line before {}",
 302                         next_thing,
 303                     ),
 304                 );
 305             }
 306         }
 307     }
 308 }
 309
 310 fn is_block(expr: &Expr) -> bool {
 311     if let ExprKind::Block(..) = expr.kind {
 312         true
 313     } else {
 314         false
 315     }
 316 }
 317
 318 /// Check if the expression is an `if` or `if let`
 319 fn is_if(expr: &Expr) -> bool {
 320     if let ExprKind::If(..) = expr.kind {
 321         true
 322     } else {
 323         false
 324     }
 325 }