clippy_lints/src/formatting.rs

   1 use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_note};
   2 use clippy_utils::differing_macro_contexts;
   3 use clippy_utils::source::snippet_opt;
   4 use if_chain::if_chain;
   5 use rustc_ast::ast::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
   6 use rustc_lint::{EarlyContext, EarlyLintPass};
   7 use rustc_middle::lint::in_external_macro;
   8 use rustc_session::{declare_lint_pass, declare_tool_lint};
   9 use rustc_span::source_map::Span;
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for use of the non-existent `=*`, `=!` and `=-`
  13     /// operators.
  14     ///
  15     /// **Why is this bad?** This is either a typo of `*=`, `!=` or `-=` or
  16     /// confusing.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     /// ```rust,ignore
  22     /// a =- 42; // confusing, should it be `a -= 42` or `a = -42`?
  23     /// ```
  24     pub SUSPICIOUS_ASSIGNMENT_FORMATTING,
  25     style,
  26     "suspicious formatting of `*=`, `-=` or `!=`"
  27 }
  28
  29 declare_clippy_lint! {
  30     /// **What it does:** Checks the formatting of a unary operator on the right hand side
  31     /// of a binary operator. It lints if there is no space between the binary and unary operators,
  32     /// but there is a space between the unary and its operand.
  33     ///
  34     /// **Why is this bad?** This is either a typo in the binary operator or confusing.
  35     ///
  36     /// **Known problems:** None.
  37     ///
  38     /// **Example:**
  39     /// ```rust,ignore
  40     /// if foo <- 30 { // this should be `foo < -30` but looks like a different operator
  41     /// }
  42     ///
  43     /// if foo &&! bar { // this should be `foo && !bar` but looks like a different operator
  44     /// }
  45     /// ```
  46     pub SUSPICIOUS_UNARY_OP_FORMATTING,
  47     style,
  48     "suspicious formatting of unary `-` or `!` on the RHS of a BinOp"
  49 }
  50
  51 declare_clippy_lint! {
  52     /// **What it does:** Checks for formatting of `else`. It lints if the `else`
  53     /// is followed immediately by a newline or the `else` seems to be missing.
  54     ///
  55     /// **Why is this bad?** This is probably some refactoring remnant, even if the
  56     /// code is correct, it might look confusing.
  57     ///
  58     /// **Known problems:** None.
  59     ///
  60     /// **Example:**
  61     /// ```rust,ignore
  62     /// if foo {
  63     /// } { // looks like an `else` is missing here
  64     /// }
  65     ///
  66     /// if foo {
  67     /// } if bar { // looks like an `else` is missing here
  68     /// }
  69     ///
  70     /// if foo {
  71     /// } else
  72     ///
  73     /// { // this is the `else` block of the previous `if`, but should it be?
  74     /// }
  75     ///
  76     /// if foo {
  77     /// } else
  78     ///
  79     /// if bar { // this is the `else` block of the previous `if`, but should it be?
  80     /// }
  81     /// ```
  82     pub SUSPICIOUS_ELSE_FORMATTING,
  83     style,
  84     "suspicious formatting of `else`"
  85 }
  86
  87 declare_clippy_lint! {
  88     /// **What it does:** Checks for possible missing comma in an array. It lints if
  89     /// an array element is a binary operator expression and it lies on two lines.
  90     ///
  91     /// **Why is this bad?** This could lead to unexpected results.
  92     ///
  93     /// **Known problems:** None.
  94     ///
  95     /// **Example:**
  96     /// ```rust,ignore
  97     /// let a = &[
  98     ///     -1, -2, -3 // <= no comma here
  99     ///     -4, -5, -6
 100     /// ];
 101     /// ```
 102     pub POSSIBLE_MISSING_COMMA,
 103     correctness,
 104     "possible missing comma in array"
 105 }
 106
 107 declare_lint_pass!(Formatting => [
 108     SUSPICIOUS_ASSIGNMENT_FORMATTING,
 109     SUSPICIOUS_UNARY_OP_FORMATTING,
 110     SUSPICIOUS_ELSE_FORMATTING,
 111     POSSIBLE_MISSING_COMMA
 112 ]);
 113
 114 impl EarlyLintPass for Formatting {
 115     fn check_block(&mut self, cx: &EarlyContext<'_>, block: &Block) {
 116         for w in block.stmts.windows(2) {
 117             if let (StmtKind::Expr(first), StmtKind::Expr(second) | StmtKind::Semi(second)) = (&w[0].kind, &w[1].kind) {
 118                 check_missing_else(cx, first, second);
 119             }
 120         }
 121     }
 122
 123     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
 124         check_assign(cx, expr);
 125         check_unop(cx, expr);
 126         check_else(cx, expr);
 127         check_array(cx, expr);
 128     }
 129 }
 130
 131 /// Implementation of the `SUSPICIOUS_ASSIGNMENT_FORMATTING` lint.
 132 fn check_assign(cx: &EarlyContext<'_>, expr: &Expr) {
 133     if let ExprKind::Assign(ref lhs, ref rhs, _) = expr.kind {
 134         if !differing_macro_contexts(lhs.span, rhs.span) && !lhs.span.from_expansion() {
 135             let eq_span = lhs.span.between(rhs.span);
 136             if let ExprKind::Unary(op, ref sub_rhs) = rhs.kind {
 137                 if let Some(eq_snippet) = snippet_opt(cx, eq_span) {
 138                     let op = UnOp::to_string(op);
 139                     let eqop_span = lhs.span.between(sub_rhs.span);
 140                     if eq_snippet.ends_with('=') {
 141                         span_lint_and_note(
 142                             cx,
 143                             SUSPICIOUS_ASSIGNMENT_FORMATTING,
 144                             eqop_span,
 145                             &format!(
 146                                 "this looks like you are trying to use `.. {op}= ..`, but you \
 147                                  really are doing `.. = ({op} ..)`",
 148                                 op = op
 149                             ),
 150                             None,
 151                             &format!("to remove this lint, use either `{op}=` or `= {op}`", op = op),
 152                         );
 153                     }
 154                 }
 155             }
 156         }
 157     }
 158 }
 159
 160 /// Implementation of the `SUSPICIOUS_UNARY_OP_FORMATTING` lint.
 161 fn check_unop(cx: &EarlyContext<'_>, expr: &Expr) {
 162     if_chain! {
 163         if let ExprKind::Binary(ref binop, ref lhs, ref rhs) = expr.kind;
 164         if !differing_macro_contexts(lhs.span, rhs.span) && !lhs.span.from_expansion();
 165         // span between BinOp LHS and RHS
 166         let binop_span = lhs.span.between(rhs.span);
 167         // if RHS is a UnOp
 168         if let ExprKind::Unary(op, ref un_rhs) = rhs.kind;
 169         // from UnOp operator to UnOp operand
 170         let unop_operand_span = rhs.span.until(un_rhs.span);
 171         if let Some(binop_snippet) = snippet_opt(cx, binop_span);
 172         if let Some(unop_operand_snippet) = snippet_opt(cx, unop_operand_span);
 173         let binop_str = BinOpKind::to_string(&binop.node);
 174         // no space after BinOp operator and space after UnOp operator
 175         if binop_snippet.ends_with(binop_str) && unop_operand_snippet.ends_with(' ');
 176         then {
 177             let unop_str = UnOp::to_string(op);
 178             let eqop_span = lhs.span.between(un_rhs.span);
 179             span_lint_and_help(
 180                 cx,
 181                 SUSPICIOUS_UNARY_OP_FORMATTING,
 182                 eqop_span,
 183                 &format!(
 184                     "by not having a space between `{binop}` and `{unop}` it looks like \
 185                      `{binop}{unop}` is a single operator",
 186                     binop = binop_str,
 187                     unop = unop_str
 188                 ),
 189                 None,
 190                 &format!(
 191                     "put a space between `{binop}` and `{unop}` and remove the space after `{unop}`",
 192                     binop = binop_str,
 193                     unop = unop_str
 194                 ),
 195             );
 196         }
 197     }
 198 }
 199
 200 /// Implementation of the `SUSPICIOUS_ELSE_FORMATTING` lint for weird `else`.
 201 fn check_else(cx: &EarlyContext<'_>, expr: &Expr) {
 202     if_chain! {
 203         if let ExprKind::If(_, then, Some(else_)) = &expr.kind;
 204         if is_block(else_) || is_if(else_);
 205         if !differing_macro_contexts(then.span, else_.span);
 206         if !then.span.from_expansion() && !in_external_macro(cx.sess, expr.span);
 207
 208         // workaround for rust-lang/rust#43081
 209         if expr.span.lo().0 != 0 && expr.span.hi().0 != 0;
 210
 211         // this will be a span from the closing ‘}’ of the “then” block (excluding) to
 212         // the “if” of the “else if” block (excluding)
 213         let else_span = then.span.between(else_.span);
 214
 215         // the snippet should look like " else \n    " with maybe comments anywhere
 216         // it’s bad when there is a ‘\n’ after the “else”
 217         if let Some(else_snippet) = snippet_opt(cx, else_span);
 218         if let Some((pre_else, post_else)) = else_snippet.split_once("else");
 219         if let Some((_, post_else_post_eol)) = post_else.split_once('\n');
 220
 221         then {
 222             // Allow allman style braces `} \n else \n {`
 223             if_chain! {
 224                 if is_block(else_);
 225                 if let Some((_, pre_else_post_eol)) = pre_else.split_once('\n');
 226                 // Exactly one eol before and after the else
 227                 if !pre_else_post_eol.contains('\n');
 228                 if !post_else_post_eol.contains('\n');
 229                 then {
 230                     return;
 231                 }
 232             }
 233
 234             let else_desc = if is_if(else_) { "if" } else { "{..}" };
 235             span_lint_and_note(
 236                 cx,
 237                 SUSPICIOUS_ELSE_FORMATTING,
 238                 else_span,
 239                 &format!("this is an `else {}` but the formatting might hide it", else_desc),
 240                 None,
 241                 &format!(
 242                     "to remove this lint, remove the `else` or remove the new line between \
 243                      `else` and `{}`",
 244                     else_desc,
 245                 ),
 246             );
 247         }
 248     }
 249 }
 250
 251 #[must_use]
 252 fn has_unary_equivalent(bin_op: BinOpKind) -> bool {
 253     // &, *, -
 254     bin_op == BinOpKind::And || bin_op == BinOpKind::Mul || bin_op == BinOpKind::Sub
 255 }
 256
 257 fn indentation(cx: &EarlyContext<'_>, span: Span) -> usize {
 258     cx.sess.source_map().lookup_char_pos(span.lo()).col.0
 259 }
 260
 261 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 262 fn check_array(cx: &EarlyContext<'_>, expr: &Expr) {
 263     if let ExprKind::Array(ref array) = expr.kind {
 264         for element in array {
 265             if_chain! {
 266                 if let ExprKind::Binary(ref op, ref lhs, _) = element.kind;
 267                 if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span);
 268                 let space_span = lhs.span.between(op.span);
 269                 if let Some(space_snippet) = snippet_opt(cx, space_span);
 270                 let lint_span = lhs.span.with_lo(lhs.span.hi());
 271                 if space_snippet.contains('\n');
 272                 if indentation(cx, op.span) <= indentation(cx, lhs.span);
 273                 then {
 274                     span_lint_and_note(
 275                         cx,
 276                         POSSIBLE_MISSING_COMMA,
 277                         lint_span,
 278                         "possibly missing a comma here",
 279                         None,
 280                         "to remove this lint, add a comma or write the expr in a single line",
 281                     );
 282                 }
 283             }
 284         }
 285     }
 286 }
 287
 288 fn check_missing_else(cx: &EarlyContext<'_>, first: &Expr, second: &Expr) {
 289     if !differing_macro_contexts(first.span, second.span)
 290         && !first.span.from_expansion()
 291         && is_if(first)
 292         && (is_block(second) || is_if(second))
 293     {
 294         // where the else would be
 295         let else_span = first.span.between(second.span);
 296
 297         if let Some(else_snippet) = snippet_opt(cx, else_span) {
 298             if !else_snippet.contains('\n') {
 299                 let (looks_like, next_thing) = if is_if(second) {
 300                     ("an `else if`", "the second `if`")
 301                 } else {
 302                     ("an `else {..}`", "the next block")
 303                 };
 304
 305                 span_lint_and_note(
 306                     cx,
 307                     SUSPICIOUS_ELSE_FORMATTING,
 308                     else_span,
 309                     &format!("this looks like {} but the `else` is missing", looks_like),
 310                     None,
 311                     &format!(
 312                         "to remove this lint, add the missing `else` or add a new line before {}",
 313                         next_thing,
 314                     ),
 315                 );
 316             }
 317         }
 318     }
 319 }
 320
 321 fn is_block(expr: &Expr) -> bool {
 322     matches!(expr.kind, ExprKind::Block(..))
 323 }
 324
 325 /// Check if the expression is an `if` or `if let`
 326 fn is_if(expr: &Expr) -> bool {
 327     matches!(expr.kind, ExprKind::If(..))
 328 }