src/tools/clippy/clippy_lints/src/booleans.rs

   1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
   2 use clippy_utils::eq_expr_value;
   3 use clippy_utils::source::snippet_opt;
   4 use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
   5 use if_chain::if_chain;
   6 use rustc_ast::ast::LitKind;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::intravisit::{walk_expr, FnKind, Visitor};
   9 use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, UnOp};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12 use rustc_span::source_map::Span;
  13 use rustc_span::sym;
  14
  15 declare_clippy_lint! {
  16     /// ### What it does
  17     /// Checks for boolean expressions that can be written more
  18     /// concisely.
  19     ///
  20     /// ### Why is this bad?
  21     /// Readability of boolean expressions suffers from
  22     /// unnecessary duplication.
  23     ///
  24     /// ### Known problems
  25     /// Ignores short circuiting behavior of `||` and
  26     /// `&&`. Ignores `|`, `&` and `^`.
  27     ///
  28     /// ### Example
  29     /// ```ignore
  30     /// if a && true {}
  31     /// if !(a == b) {}
  32     /// ```
  33     ///
  34     /// Use instead:
  35     /// ```rust,ignore
  36     /// if a {}
  37     /// if a != b {}
  38     /// ```
  39     #[clippy::version = "pre 1.29.0"]
  40     pub NONMINIMAL_BOOL,
  41     complexity,
  42     "boolean expressions that can be written more concisely"
  43 }
  44
  45 declare_clippy_lint! {
  46     /// ### What it does
  47     /// Checks for boolean expressions that contain terminals that
  48     /// can be eliminated.
  49     ///
  50     /// ### Why is this bad?
  51     /// This is most likely a logic bug.
  52     ///
  53     /// ### Known problems
  54     /// Ignores short circuiting behavior.
  55     ///
  56     /// ### Example
  57     /// ```rust,ignore
  58     /// // The `b` is unnecessary, the expression is equivalent to `if a`.
  59     /// if a && b || a { ... }
  60     /// ```
  61     ///
  62     /// Use instead:
  63     /// ```rust,ignore
  64     /// if a {}
  65     /// ```
  66     #[clippy::version = "pre 1.29.0"]
  67     pub OVERLY_COMPLEX_BOOL_EXPR,
  68     correctness,
  69     "boolean expressions that contain terminals which can be eliminated"
  70 }
  71
  72 // For each pairs, both orders are considered.
  73 const METHODS_WITH_NEGATION: [(&str, &str); 2] = [("is_some", "is_none"), ("is_err", "is_ok")];
  74
  75 declare_lint_pass!(NonminimalBool => [NONMINIMAL_BOOL, OVERLY_COMPLEX_BOOL_EXPR]);
  76
  77 impl<'tcx> LateLintPass<'tcx> for NonminimalBool {
  78     fn check_fn(
  79         &mut self,
  80         cx: &LateContext<'tcx>,
  81         _: FnKind<'tcx>,
  82         _: &'tcx FnDecl<'_>,
  83         body: &'tcx Body<'_>,
  84         _: Span,
  85         _: HirId,
  86     ) {
  87         NonminimalBoolVisitor { cx }.visit_body(body);
  88     }
  89 }
  90
  91 struct NonminimalBoolVisitor<'a, 'tcx> {
  92     cx: &'a LateContext<'tcx>,
  93 }
  94
  95 use quine_mc_cluskey::Bool;
  96 struct Hir2Qmm<'a, 'tcx, 'v> {
  97     terminals: Vec<&'v Expr<'v>>,
  98     cx: &'a LateContext<'tcx>,
  99 }
 100
 101 impl<'a, 'tcx, 'v> Hir2Qmm<'a, 'tcx, 'v> {
 102     fn extract(&mut self, op: BinOpKind, a: &[&'v Expr<'_>], mut v: Vec<Bool>) -> Result<Vec<Bool>, String> {
 103         for a in a {
 104             if let ExprKind::Binary(binop, lhs, rhs) = &a.kind {
 105                 if binop.node == op {
 106                     v = self.extract(op, &[lhs, rhs], v)?;
 107                     continue;
 108                 }
 109             }
 110             v.push(self.run(a)?);
 111         }
 112         Ok(v)
 113     }
 114
 115     fn run(&mut self, e: &'v Expr<'_>) -> Result<Bool, String> {
 116         fn negate(bin_op_kind: BinOpKind) -> Option<BinOpKind> {
 117             match bin_op_kind {
 118                 BinOpKind::Eq => Some(BinOpKind::Ne),
 119                 BinOpKind::Ne => Some(BinOpKind::Eq),
 120                 BinOpKind::Gt => Some(BinOpKind::Le),
 121                 BinOpKind::Ge => Some(BinOpKind::Lt),
 122                 BinOpKind::Lt => Some(BinOpKind::Ge),
 123                 BinOpKind::Le => Some(BinOpKind::Gt),
 124                 _ => None,
 125             }
 126         }
 127
 128         // prevent folding of `cfg!` macros and the like
 129         if !e.span.from_expansion() {
 130             match &e.kind {
 131                 ExprKind::Unary(UnOp::Not, inner) => return Ok(Bool::Not(Box::new(self.run(inner)?))),
 132                 ExprKind::Binary(binop, lhs, rhs) => match &binop.node {
 133                     BinOpKind::Or => {
 134                         return Ok(Bool::Or(self.extract(BinOpKind::Or, &[lhs, rhs], Vec::new())?));
 135                     },
 136                     BinOpKind::And => {
 137                         return Ok(Bool::And(self.extract(BinOpKind::And, &[lhs, rhs], Vec::new())?));
 138                     },
 139                     _ => (),
 140                 },
 141                 ExprKind::Lit(lit) => match lit.node {
 142                     LitKind::Bool(true) => return Ok(Bool::True),
 143                     LitKind::Bool(false) => return Ok(Bool::False),
 144                     _ => (),
 145                 },
 146                 _ => (),
 147             }
 148         }
 149         for (n, expr) in self.terminals.iter().enumerate() {
 150             if eq_expr_value(self.cx, e, expr) {
 151                 #[expect(clippy::cast_possible_truncation)]
 152                 return Ok(Bool::Term(n as u8));
 153             }
 154
 155             if_chain! {
 156                 if let ExprKind::Binary(e_binop, e_lhs, e_rhs) = &e.kind;
 157                 if implements_ord(self.cx, e_lhs);
 158                 if let ExprKind::Binary(expr_binop, expr_lhs, expr_rhs) = &expr.kind;
 159                 if negate(e_binop.node) == Some(expr_binop.node);
 160                 if eq_expr_value(self.cx, e_lhs, expr_lhs);
 161                 if eq_expr_value(self.cx, e_rhs, expr_rhs);
 162                 then {
 163                     #[expect(clippy::cast_possible_truncation)]
 164                     return Ok(Bool::Not(Box::new(Bool::Term(n as u8))));
 165                 }
 166             }
 167         }
 168         let n = self.terminals.len();
 169         self.terminals.push(e);
 170         if n < 32 {
 171             #[expect(clippy::cast_possible_truncation)]
 172             Ok(Bool::Term(n as u8))
 173         } else {
 174             Err("too many literals".to_owned())
 175         }
 176     }
 177 }
 178
 179 struct SuggestContext<'a, 'tcx, 'v> {
 180     terminals: &'v [&'v Expr<'v>],
 181     cx: &'a LateContext<'tcx>,
 182     output: String,
 183 }
 184
 185 impl<'a, 'tcx, 'v> SuggestContext<'a, 'tcx, 'v> {
 186     fn recurse(&mut self, suggestion: &Bool) -> Option<()> {
 187         use quine_mc_cluskey::Bool::{And, False, Not, Or, Term, True};
 188         match suggestion {
 189             True => {
 190                 self.output.push_str("true");
 191             },
 192             False => {
 193                 self.output.push_str("false");
 194             },
 195             Not(inner) => match **inner {
 196                 And(_) | Or(_) => {
 197                     self.output.push('!');
 198                     self.output.push('(');
 199                     self.recurse(inner);
 200                     self.output.push(')');
 201                 },
 202                 Term(n) => {
 203                     let terminal = self.terminals[n as usize];
 204                     if let Some(str) = simplify_not(self.cx, terminal) {
 205                         self.output.push_str(&str);
 206                     } else {
 207                         self.output.push('!');
 208                         let snip = snippet_opt(self.cx, terminal.span)?;
 209                         self.output.push_str(&snip);
 210                     }
 211                 },
 212                 True | False | Not(_) => {
 213                     self.output.push('!');
 214                     self.recurse(inner)?;
 215                 },
 216             },
 217             And(v) => {
 218                 for (index, inner) in v.iter().enumerate() {
 219                     if index > 0 {
 220                         self.output.push_str(" && ");
 221                     }
 222                     if let Or(_) = *inner {
 223                         self.output.push('(');
 224                         self.recurse(inner);
 225                         self.output.push(')');
 226                     } else {
 227                         self.recurse(inner);
 228                     }
 229                 }
 230             },
 231             Or(v) => {
 232                 for (index, inner) in v.iter().rev().enumerate() {
 233                     if index > 0 {
 234                         self.output.push_str(" || ");
 235                     }
 236                     self.recurse(inner);
 237                 }
 238             },
 239             &Term(n) => {
 240                 let snip = snippet_opt(self.cx, self.terminals[n as usize].span.source_callsite())?;
 241                 self.output.push_str(&snip);
 242             },
 243         }
 244         Some(())
 245     }
 246 }
 247
 248 fn simplify_not(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<String> {
 249     match &expr.kind {
 250         ExprKind::Binary(binop, lhs, rhs) => {
 251             if !implements_ord(cx, lhs) {
 252                 return None;
 253             }
 254
 255             match binop.node {
 256                 BinOpKind::Eq => Some(" != "),
 257                 BinOpKind::Ne => Some(" == "),
 258                 BinOpKind::Lt => Some(" >= "),
 259                 BinOpKind::Gt => Some(" <= "),
 260                 BinOpKind::Le => Some(" > "),
 261                 BinOpKind::Ge => Some(" < "),
 262                 _ => None,
 263             }
 264             .and_then(|op| {
 265                 Some(format!(
 266                     "{}{op}{}",
 267                     snippet_opt(cx, lhs.span)?,
 268                     snippet_opt(cx, rhs.span)?
 269                 ))
 270             })
 271         },
 272         ExprKind::MethodCall(path, receiver, [], _) => {
 273             let type_of_receiver = cx.typeck_results().expr_ty(receiver);
 274             if !is_type_diagnostic_item(cx, type_of_receiver, sym::Option)
 275                 && !is_type_diagnostic_item(cx, type_of_receiver, sym::Result)
 276             {
 277                 return None;
 278             }
 279             METHODS_WITH_NEGATION
 280                 .iter()
 281                 .copied()
 282                 .flat_map(|(a, b)| vec![(a, b), (b, a)])
 283                 .find(|&(a, _)| {
 284                     let path: &str = path.ident.name.as_str();
 285                     a == path
 286                 })
 287                 .and_then(|(_, neg_method)| Some(format!("{}.{neg_method}()", snippet_opt(cx, receiver.span)?)))
 288         },
 289         _ => None,
 290     }
 291 }
 292
 293 fn suggest(cx: &LateContext<'_>, suggestion: &Bool, terminals: &[&Expr<'_>]) -> String {
 294     let mut suggest_context = SuggestContext {
 295         terminals,
 296         cx,
 297         output: String::new(),
 298     };
 299     suggest_context.recurse(suggestion);
 300     suggest_context.output
 301 }
 302
 303 fn simple_negate(b: Bool) -> Bool {
 304     use quine_mc_cluskey::Bool::{And, False, Not, Or, Term, True};
 305     match b {
 306         True => False,
 307         False => True,
 308         t @ Term(_) => Not(Box::new(t)),
 309         And(mut v) => {
 310             for el in &mut v {
 311                 *el = simple_negate(::std::mem::replace(el, True));
 312             }
 313             Or(v)
 314         },
 315         Or(mut v) => {
 316             for el in &mut v {
 317                 *el = simple_negate(::std::mem::replace(el, True));
 318             }
 319             And(v)
 320         },
 321         Not(inner) => *inner,
 322     }
 323 }
 324
 325 #[derive(Default)]
 326 struct Stats {
 327     terminals: [usize; 32],
 328     negations: usize,
 329     ops: usize,
 330 }
 331
 332 fn terminal_stats(b: &Bool) -> Stats {
 333     fn recurse(b: &Bool, stats: &mut Stats) {
 334         match b {
 335             True | False => stats.ops += 1,
 336             Not(inner) => {
 337                 match **inner {
 338                     And(_) | Or(_) => stats.ops += 1, // brackets are also operations
 339                     _ => stats.negations += 1,
 340                 }
 341                 recurse(inner, stats);
 342             },
 343             And(v) | Or(v) => {
 344                 stats.ops += v.len() - 1;
 345                 for inner in v {
 346                     recurse(inner, stats);
 347                 }
 348             },
 349             &Term(n) => stats.terminals[n as usize] += 1,
 350         }
 351     }
 352     use quine_mc_cluskey::Bool::{And, False, Not, Or, Term, True};
 353     let mut stats = Stats::default();
 354     recurse(b, &mut stats);
 355     stats
 356 }
 357
 358 impl<'a, 'tcx> NonminimalBoolVisitor<'a, 'tcx> {
 359     fn bool_expr(&self, e: &'tcx Expr<'_>) {
 360         let mut h2q = Hir2Qmm {
 361             terminals: Vec::new(),
 362             cx: self.cx,
 363         };
 364         if let Ok(expr) = h2q.run(e) {
 365             if h2q.terminals.len() > 8 {
 366                 // QMC has exponentially slow behavior as the number of terminals increases
 367                 // 8 is reasonable, it takes approximately 0.2 seconds.
 368                 // See #825
 369                 return;
 370             }
 371
 372             let stats = terminal_stats(&expr);
 373             let mut simplified = expr.simplify();
 374             for simple in Bool::Not(Box::new(expr)).simplify() {
 375                 match simple {
 376                     Bool::Not(_) | Bool::True | Bool::False => {},
 377                     _ => simplified.push(Bool::Not(Box::new(simple.clone()))),
 378                 }
 379                 let simple_negated = simple_negate(simple);
 380                 if simplified.iter().any(|s| *s == simple_negated) {
 381                     continue;
 382                 }
 383                 simplified.push(simple_negated);
 384             }
 385             let mut improvements = Vec::with_capacity(simplified.len());
 386             'simplified: for suggestion in &simplified {
 387                 let simplified_stats = terminal_stats(suggestion);
 388                 let mut improvement = false;
 389                 for i in 0..32 {
 390                     // ignore any "simplifications" that end up requiring a terminal more often
 391                     // than in the original expression
 392                     if stats.terminals[i] < simplified_stats.terminals[i] {
 393                         continue 'simplified;
 394                     }
 395                     if stats.terminals[i] != 0 && simplified_stats.terminals[i] == 0 {
 396                         span_lint_hir_and_then(
 397                             self.cx,
 398                             OVERLY_COMPLEX_BOOL_EXPR,
 399                             e.hir_id,
 400                             e.span,
 401                             "this boolean expression contains a logic bug",
 402                             |diag| {
 403                                 diag.span_help(
 404                                     h2q.terminals[i].span,
 405                                     "this expression can be optimized out by applying boolean operations to the \
 406                                      outer expression",
 407                                 );
 408                                 diag.span_suggestion(
 409                                     e.span,
 410                                     "it would look like the following",
 411                                     suggest(self.cx, suggestion, &h2q.terminals),
 412                                     // nonminimal_bool can produce minimal but
 413                                     // not human readable expressions (#3141)
 414                                     Applicability::Unspecified,
 415                                 );
 416                             },
 417                         );
 418                         // don't also lint `NONMINIMAL_BOOL`
 419                         return;
 420                     }
 421                     // if the number of occurrences of a terminal decreases or any of the stats
 422                     // decreases while none increases
 423                     improvement |= (stats.terminals[i] > simplified_stats.terminals[i])
 424                         || (stats.negations > simplified_stats.negations && stats.ops == simplified_stats.ops)
 425                         || (stats.ops > simplified_stats.ops && stats.negations == simplified_stats.negations);
 426                 }
 427                 if improvement {
 428                     improvements.push(suggestion);
 429                 }
 430             }
 431             let nonminimal_bool_lint = |suggestions: Vec<_>| {
 432                 span_lint_hir_and_then(
 433                     self.cx,
 434                     NONMINIMAL_BOOL,
 435                     e.hir_id,
 436                     e.span,
 437                     "this boolean expression can be simplified",
 438                     |diag| {
 439                         diag.span_suggestions(
 440                             e.span,
 441                             "try",
 442                             suggestions.into_iter(),
 443                             // nonminimal_bool can produce minimal but
 444                             // not human readable expressions (#3141)
 445                             Applicability::Unspecified,
 446                         );
 447                     },
 448                 );
 449             };
 450             if improvements.is_empty() {
 451                 let mut visitor = NotSimplificationVisitor { cx: self.cx };
 452                 visitor.visit_expr(e);
 453             } else {
 454                 nonminimal_bool_lint(
 455                     improvements
 456                         .into_iter()
 457                         .map(|suggestion| suggest(self.cx, suggestion, &h2q.terminals))
 458                         .collect(),
 459                 );
 460             }
 461         }
 462     }
 463 }
 464
 465 impl<'a, 'tcx> Visitor<'tcx> for NonminimalBoolVisitor<'a, 'tcx> {
 466     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
 467         if !e.span.from_expansion() {
 468             match &e.kind {
 469                 ExprKind::Binary(binop, _, _) if binop.node == BinOpKind::Or || binop.node == BinOpKind::And => {
 470                     self.bool_expr(e);
 471                 },
 472                 ExprKind::Unary(UnOp::Not, inner) => {
 473                     if self.cx.typeck_results().node_types()[inner.hir_id].is_bool() {
 474                         self.bool_expr(e);
 475                     }
 476                 },
 477                 _ => {},
 478             }
 479         }
 480         walk_expr(self, e);
 481     }
 482 }
 483
 484 fn implements_ord(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 485     let ty = cx.typeck_results().expr_ty(expr);
 486     cx.tcx
 487         .get_diagnostic_item(sym::Ord)
 488         .map_or(false, |id| implements_trait(cx, ty, id, &[]))
 489 }
 490
 491 struct NotSimplificationVisitor<'a, 'tcx> {
 492     cx: &'a LateContext<'tcx>,
 493 }
 494
 495 impl<'a, 'tcx> Visitor<'tcx> for NotSimplificationVisitor<'a, 'tcx> {
 496     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
 497         if let ExprKind::Unary(UnOp::Not, inner) = &expr.kind {
 498             if let Some(suggestion) = simplify_not(self.cx, inner) {
 499                 span_lint_and_sugg(
 500                     self.cx,
 501                     NONMINIMAL_BOOL,
 502                     expr.span,
 503                     "this boolean expression can be simplified",
 504                     "try",
 505                     suggestion,
 506                     Applicability::MachineApplicable,
 507                 );
 508             }
 509         }
 510
 511         walk_expr(self, expr);
 512     }
 513 }