1 //! Checks for needless boolean results of if-else expressions
3 //! This lint is **warn** by default
5 use crate::utils::sugg::Sugg;
7 higher, is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg,
9 use if_chain::if_chain;
10 use rustc_ast::ast::LitKind;
11 use rustc_errors::Applicability;
12 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
13 use rustc_lint::{LateContext, LateLintPass};
14 use rustc_session::{declare_lint_pass, declare_tool_lint};
15 use rustc_span::source_map::Spanned;
18 declare_clippy_lint! {
19 /// **What it does:** Checks for expressions of the form `if c { true } else {
20 /// false }` (or vice versa) and suggests using the condition directly.
22 /// **Why is this bad?** Redundant code.
24 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
25 /// painstakingly documented (which we, of course, do not detect), so they *may*
26 /// have some value. Even then, the documentation can be rewritten to match the
37 /// Could be written as
43 "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
46 declare_clippy_lint! {
47 /// **What it does:** Checks for expressions of the form `x == true`,
48 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
49 /// suggest using the variable directly.
51 /// **Why is this bad?** Unnecessary code.
53 /// **Known problems:** None.
67 "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
70 declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
72 impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
73 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
74 use self::Expression::{Bool, RetBool};
75 if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
76 let reduce = |ret, not| {
77 let mut applicability = Applicability::MachineApplicable;
78 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
79 let mut snip = if not { !snip } else { snip };
82 snip = snip.make_return();
85 if parent_node_is_if_expr(&e, &cx) {
86 snip = snip.blockify()
93 "this if-then-else expression returns a bool literal",
94 "you can reduce it to",
99 if let ExprKind::Block(ref then_block, _) = then_block.kind {
100 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
101 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
106 "this if-then-else expression will always return true",
109 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
114 "this if-then-else expression will always return false",
117 (RetBool(true), RetBool(false)) => reduce(true, false),
118 (Bool(true), Bool(false)) => reduce(false, false),
119 (RetBool(false), RetBool(true)) => reduce(true, true),
120 (Bool(false), Bool(true)) => reduce(false, true),
124 panic!("IfExpr `then` node is not an `ExprKind::Block`");
130 declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
132 impl<'tcx> LateLintPass<'tcx> for BoolComparison {
133 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
134 if e.span.from_expansion() {
138 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
139 let ignore_case = None::<(fn(_) -> _, &str)>;
140 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
143 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
144 let false_case = Some((
146 "equality checks against false can be replaced by a negation",
148 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
151 let true_case = Some((
153 "inequality checks against true can be replaced by a negation",
155 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
156 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
158 BinOpKind::Lt => check_comparison(
162 Some((|h| h, "greater than checks against false are unnecessary")),
165 "less than comparison against true can be replaced by a negation",
169 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
170 "order comparisons between booleans can be simplified",
173 BinOpKind::Gt => check_comparison(
178 "less than comparison against true can be replaced by a negation",
182 Some((|h| h, "greater than checks against false are unnecessary")),
184 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
185 "order comparisons between booleans can be simplified",
194 struct ExpressionInfoWithSpan {
195 one_side_is_unary_not: bool,
200 fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
202 if let ExprKind::Unary(unop, operand) = e.kind;
203 if let UnOp::UnNot = unop;
205 return (true, operand.span);
211 fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
212 let left = is_unary_not(left_side);
213 let right = is_unary_not(right_side);
215 ExpressionInfoWithSpan {
216 one_side_is_unary_not: left.0 != right.0,
222 fn check_comparison<'a, 'tcx>(
223 cx: &LateContext<'tcx>,
225 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
226 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
227 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
228 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
229 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
231 use self::Expression::{Bool, Other};
233 if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
235 cx.typeck_results().expr_ty(left_side),
236 cx.typeck_results().expr_ty(right_side),
238 if is_expn_of(left_side.span, "cfg").is_some() || is_expn_of(right_side.span, "cfg").is_some() {
241 if l_ty.is_bool() && r_ty.is_bool() {
242 let mut applicability = Applicability::MachineApplicable;
244 if let BinOpKind::Eq = op.node {
245 let expression_info = one_side_is_unary_not(&left_side, &right_side);
246 if expression_info.one_side_is_unary_not {
251 "this comparison might be written more concisely",
252 "try simplifying it as shown",
255 snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
256 snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
263 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
264 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
265 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
267 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
268 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
270 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
271 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
273 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
274 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
276 (Other, Other) => no_literal.map_or((), |(h, m)| {
277 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
278 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
284 "try simplifying it as shown",
285 h(left_side, right_side).to_string(),
295 fn suggest_bool_comparison<'a, 'tcx>(
296 cx: &LateContext<'tcx>,
299 mut applicability: Applicability,
301 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
303 let hint = if expr.span.from_expansion() {
304 if applicability != Applicability::Unspecified {
305 applicability = Applicability::MaybeIncorrect;
307 Sugg::hir_with_macro_callsite(cx, expr, "..")
309 Sugg::hir_with_applicability(cx, expr, "..", &mut applicability)
316 "try simplifying it as shown",
317 conv_hint(hint).to_string(),
328 fn fetch_bool_block(block: &Block<'_>) -> Expression {
329 match (&*block.stmts, block.expr.as_ref()) {
330 (&[], Some(e)) => fetch_bool_expr(&**e),
331 (&[ref e], None) => {
332 if let StmtKind::Semi(ref e) = e.kind {
333 if let ExprKind::Ret(_) = e.kind {
334 fetch_bool_expr(&**e)
342 _ => Expression::Other,
346 fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
348 ExprKind::Block(ref block, _) => fetch_bool_block(block),
349 ExprKind::Lit(ref lit_ptr) => {
350 if let LitKind::Bool(value) = lit_ptr.node {
351 Expression::Bool(value)
356 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
357 Expression::Bool(value) => Expression::RetBool(value),
358 _ => Expression::Other,
360 _ => Expression::Other,