1 //! Checks for needless boolean results of if-else expressions
3 //! This lint is **warn** by default
5 use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
6 use clippy_utils::source::snippet_with_applicability;
7 use clippy_utils::sugg::Sugg;
8 use clippy_utils::{is_else_clause, is_expn_of};
9 use rustc_ast::ast::LitKind;
10 use rustc_errors::Applicability;
11 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
12 use rustc_lint::{LateContext, LateLintPass};
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 use rustc_span::source_map::Spanned;
17 declare_clippy_lint! {
18 /// **What it does:** Checks for expressions of the form `if c { true } else {
19 /// false }` (or vice versa) and suggests using the condition directly.
21 /// **Why is this bad?** Redundant code.
23 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
24 /// painstakingly documented (which we, of course, do not detect), so they *may*
25 /// have some value. Even then, the documentation can be rewritten to match the
36 /// Could be written as
42 "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
45 declare_clippy_lint! {
46 /// **What it does:** Checks for expressions of the form `x == true`,
47 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
48 /// suggest using the variable directly.
50 /// **Why is this bad?** Unnecessary code.
52 /// **Known problems:** None.
66 "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
69 declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
71 impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
72 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
73 use self::Expression::{Bool, RetBool};
74 if let ExprKind::If(pred, then_block, Some(else_expr)) = e.kind {
75 let reduce = |ret, not| {
76 let mut applicability = Applicability::MachineApplicable;
77 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
78 let mut snip = if not { !snip } else { snip };
81 snip = snip.make_return();
84 if is_else_clause(cx.tcx, e) {
85 snip = snip.blockify();
92 "this if-then-else expression returns a bool literal",
93 "you can reduce it to",
98 if let ExprKind::Block(then_block, _) = then_block.kind {
99 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
100 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
105 "this if-then-else expression will always return true",
108 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
113 "this if-then-else expression will always return false",
116 (RetBool(true), RetBool(false)) => reduce(true, false),
117 (Bool(true), Bool(false)) => reduce(false, false),
118 (RetBool(false), RetBool(true)) => reduce(true, true),
119 (Bool(false), Bool(true)) => reduce(false, true),
123 panic!("IfExpr `then` node is not an `ExprKind::Block`");
129 declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
131 impl<'tcx> LateLintPass<'tcx> for BoolComparison {
132 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
133 if e.span.from_expansion() {
137 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
138 let ignore_case = None::<(fn(_) -> _, &str)>;
139 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
142 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
143 let false_case = Some((
145 "equality checks against false can be replaced by a negation",
147 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal);
150 let true_case = Some((
152 "inequality checks against true can be replaced by a negation",
154 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
155 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal);
157 BinOpKind::Lt => check_comparison(
161 Some((|h| h, "greater than checks against false are unnecessary")),
164 "less than comparison against true can be replaced by a negation",
168 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
169 "order comparisons between booleans can be simplified",
172 BinOpKind::Gt => check_comparison(
177 "less than comparison against true can be replaced by a negation",
181 Some((|h| h, "greater than checks against false are unnecessary")),
183 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
184 "order comparisons between booleans can be simplified",
193 struct ExpressionInfoWithSpan {
194 one_side_is_unary_not: bool,
199 fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
200 if let ExprKind::Unary(UnOp::Not, operand) = e.kind {
201 return (true, operand.span);
206 fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
207 let left = is_unary_not(left_side);
208 let right = is_unary_not(right_side);
210 ExpressionInfoWithSpan {
211 one_side_is_unary_not: left.0 != right.0,
217 fn check_comparison<'a, 'tcx>(
218 cx: &LateContext<'tcx>,
220 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
221 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
222 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
223 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
224 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
226 use self::Expression::{Bool, Other};
228 if let ExprKind::Binary(op, left_side, right_side) = e.kind {
230 cx.typeck_results().expr_ty(left_side),
231 cx.typeck_results().expr_ty(right_side),
233 if is_expn_of(left_side.span, "cfg").is_some() || is_expn_of(right_side.span, "cfg").is_some() {
236 if l_ty.is_bool() && r_ty.is_bool() {
237 let mut applicability = Applicability::MachineApplicable;
239 if let BinOpKind::Eq = op.node {
240 let expression_info = one_side_is_unary_not(left_side, right_side);
241 if expression_info.one_side_is_unary_not {
246 "this comparison might be written more concisely",
247 "try simplifying it as shown",
250 snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
251 snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
258 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
259 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
260 suggest_bool_comparison(cx, e, right_side, applicability, m, h);
262 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
263 suggest_bool_comparison(cx, e, left_side, applicability, m, h);
265 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
266 suggest_bool_comparison(cx, e, right_side, applicability, m, h);
268 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
269 suggest_bool_comparison(cx, e, left_side, applicability, m, h);
271 (Other, Other) => no_literal.map_or((), |(h, m)| {
272 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
273 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
279 "try simplifying it as shown",
280 h(left_side, right_side).to_string(),
290 fn suggest_bool_comparison<'a, 'tcx>(
291 cx: &LateContext<'tcx>,
294 mut applicability: Applicability,
296 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
298 let hint = if expr.span.from_expansion() {
299 if applicability != Applicability::Unspecified {
300 applicability = Applicability::MaybeIncorrect;
302 Sugg::hir_with_macro_callsite(cx, expr, "..")
304 Sugg::hir_with_applicability(cx, expr, "..", &mut applicability)
311 "try simplifying it as shown",
312 conv_hint(hint).to_string(),
323 fn fetch_bool_block(block: &Block<'_>) -> Expression {
324 match (&*block.stmts, block.expr.as_ref()) {
325 (&[], Some(e)) => fetch_bool_expr(&**e),
326 (&[ref e], None) => {
327 if let StmtKind::Semi(e) = e.kind {
328 if let ExprKind::Ret(_) = e.kind {
337 _ => Expression::Other,
341 fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
343 ExprKind::Block(block, _) => fetch_bool_block(block),
344 ExprKind::Lit(ref lit_ptr) => {
345 if let LitKind::Bool(value) = lit_ptr.node {
346 Expression::Bool(value)
351 ExprKind::Ret(Some(expr)) => match fetch_bool_expr(expr) {
352 Expression::Bool(value) => Expression::RetBool(value),
353 _ => Expression::Other,
355 _ => Expression::Other,