1 //! Checks for needless boolean results of if-else expressions
3 //! This lint is **warn** by default
5 use crate::utils::sugg::Sugg;
6 use crate::utils::{is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg};
7 use rustc_ast::ast::LitKind;
8 use rustc_errors::Applicability;
9 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
10 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::source_map::Spanned;
15 declare_clippy_lint! {
16 /// **What it does:** Checks for expressions of the form `if c { true } else {
17 /// false }` (or vice versa) and suggests using the condition directly.
19 /// **Why is this bad?** Redundant code.
21 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
22 /// painstakingly documented (which we, of course, do not detect), so they *may*
23 /// have some value. Even then, the documentation can be rewritten to match the
34 /// Could be written as
40 "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
43 declare_clippy_lint! {
44 /// **What it does:** Checks for expressions of the form `x == true`,
45 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
46 /// suggest using the variable directly.
48 /// **Why is this bad?** Unnecessary code.
50 /// **Known problems:** None.
64 "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
67 declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
69 impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
70 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
71 use self::Expression::{Bool, RetBool};
72 if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.kind {
73 let reduce = |ret, not| {
74 let mut applicability = Applicability::MachineApplicable;
75 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
76 let mut snip = if not { !snip } else { snip };
79 snip = snip.make_return();
82 if parent_node_is_if_expr(&e, &cx) {
83 snip = snip.blockify()
90 "this if-then-else expression returns a bool literal",
91 "you can reduce it to",
96 if let ExprKind::Block(ref then_block, _) = then_block.kind {
97 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
98 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
103 "this if-then-else expression will always return true",
106 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
111 "this if-then-else expression will always return false",
114 (RetBool(true), RetBool(false)) => reduce(true, false),
115 (Bool(true), Bool(false)) => reduce(false, false),
116 (RetBool(false), RetBool(true)) => reduce(true, true),
117 (Bool(false), Bool(true)) => reduce(false, true),
121 panic!("IfExpr `then` node is not an `ExprKind::Block`");
127 declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
129 impl<'tcx> LateLintPass<'tcx> for BoolComparison {
130 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
131 if e.span.from_expansion() {
135 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
136 let ignore_case = None::<(fn(_) -> _, &str)>;
137 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
140 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
141 let false_case = Some((
143 "equality checks against false can be replaced by a negation",
145 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
148 let true_case = Some((
150 "inequality checks against true can be replaced by a negation",
152 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
153 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
155 BinOpKind::Lt => check_comparison(
159 Some((|h| h, "greater than checks against false are unnecessary")),
162 "less than comparison against true can be replaced by a negation",
166 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
167 "order comparisons between booleans can be simplified",
170 BinOpKind::Gt => check_comparison(
175 "less than comparison against true can be replaced by a negation",
179 Some((|h| h, "greater than checks against false are unnecessary")),
181 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
182 "order comparisons between booleans can be simplified",
191 struct ExpressionInfoWithSpan {
192 one_side_is_unary_not: bool,
197 fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
198 if let ExprKind::Unary(UnOp::UnNot, operand) = e.kind {
199 return (true, operand.span);
204 fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
205 let left = is_unary_not(left_side);
206 let right = is_unary_not(right_side);
208 ExpressionInfoWithSpan {
209 one_side_is_unary_not: left.0 != right.0,
215 fn check_comparison<'a, 'tcx>(
216 cx: &LateContext<'tcx>,
218 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
219 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
220 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
221 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
222 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
224 use self::Expression::{Bool, Other};
226 if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
228 cx.typeck_results().expr_ty(left_side),
229 cx.typeck_results().expr_ty(right_side),
231 if is_expn_of(left_side.span, "cfg").is_some() || is_expn_of(right_side.span, "cfg").is_some() {
234 if l_ty.is_bool() && r_ty.is_bool() {
235 let mut applicability = Applicability::MachineApplicable;
237 if let BinOpKind::Eq = op.node {
238 let expression_info = one_side_is_unary_not(&left_side, &right_side);
239 if expression_info.one_side_is_unary_not {
244 "this comparison might be written more concisely",
245 "try simplifying it as shown",
248 snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
249 snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
256 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
257 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
258 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
260 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
261 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
263 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
264 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
266 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
267 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
269 (Other, Other) => no_literal.map_or((), |(h, m)| {
270 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
271 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
277 "try simplifying it as shown",
278 h(left_side, right_side).to_string(),
288 fn suggest_bool_comparison<'a, 'tcx>(
289 cx: &LateContext<'tcx>,
292 mut applicability: Applicability,
294 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
296 let hint = if expr.span.from_expansion() {
297 if applicability != Applicability::Unspecified {
298 applicability = Applicability::MaybeIncorrect;
300 Sugg::hir_with_macro_callsite(cx, expr, "..")
302 Sugg::hir_with_applicability(cx, expr, "..", &mut applicability)
309 "try simplifying it as shown",
310 conv_hint(hint).to_string(),
321 fn fetch_bool_block(block: &Block<'_>) -> Expression {
322 match (&*block.stmts, block.expr.as_ref()) {
323 (&[], Some(e)) => fetch_bool_expr(&**e),
324 (&[ref e], None) => {
325 if let StmtKind::Semi(ref e) = e.kind {
326 if let ExprKind::Ret(_) = e.kind {
327 fetch_bool_expr(&**e)
335 _ => Expression::Other,
339 fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
341 ExprKind::Block(ref block, _) => fetch_bool_block(block),
342 ExprKind::Lit(ref lit_ptr) => {
343 if let LitKind::Bool(value) = lit_ptr.node {
344 Expression::Bool(value)
349 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
350 Expression::Bool(value) => Expression::RetBool(value),
351 _ => Expression::Other,
353 _ => Expression::Other,