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::{higher, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg};
7 use if_chain::if_chain;
8 use rustc_ast::ast::LitKind;
9 use rustc_errors::Applicability;
10 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Spanned;
16 declare_clippy_lint! {
17 /// **What it does:** Checks for expressions of the form `if c { true } else {
18 /// false }` (or vice versa) and suggests using the condition directly.
20 /// **Why is this bad?** Redundant code.
22 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
23 /// painstakingly documented (which we, of course, do not detect), so they *may*
24 /// have some value. Even then, the documentation can be rewritten to match the
35 /// Could be written as
41 "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
44 declare_clippy_lint! {
45 /// **What it does:** Checks for expressions of the form `x == true`,
46 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
47 /// suggest using the variable directly.
49 /// **Why is this bad?** Unnecessary code.
51 /// **Known problems:** None.
65 "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
68 declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
70 impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
71 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
72 use self::Expression::{Bool, RetBool};
73 if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
74 let reduce = |ret, not| {
75 let mut applicability = Applicability::MachineApplicable;
76 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
77 let mut snip = if not { !snip } else { snip };
80 snip = snip.make_return();
83 if parent_node_is_if_expr(&e, &cx) {
84 snip = snip.blockify()
91 "this if-then-else expression returns a bool literal",
92 "you can reduce it to",
97 if let ExprKind::Block(ref then_block, _) = then_block.kind {
98 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
99 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
104 "this if-then-else expression will always return true",
107 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
112 "this if-then-else expression will always return false",
115 (RetBool(true), RetBool(false)) => reduce(true, false),
116 (Bool(true), Bool(false)) => reduce(false, false),
117 (RetBool(false), RetBool(true)) => reduce(true, true),
118 (Bool(false), Bool(true)) => reduce(false, true),
122 panic!("IfExpr `then` node is not an `ExprKind::Block`");
128 declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
130 impl<'tcx> LateLintPass<'tcx> for BoolComparison {
131 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
132 if e.span.from_expansion() {
136 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
137 let ignore_case = None::<(fn(_) -> _, &str)>;
138 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
141 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
142 let false_case = Some((
144 "equality checks against false can be replaced by a negation",
146 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
149 let true_case = Some((
151 "inequality checks against true can be replaced by a negation",
153 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
154 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
156 BinOpKind::Lt => check_comparison(
160 Some((|h| h, "greater than checks against false are unnecessary")),
163 "less than comparison against true can be replaced by a negation",
167 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
168 "order comparisons between booleans can be simplified",
171 BinOpKind::Gt => check_comparison(
176 "less than comparison against true can be replaced by a negation",
180 Some((|h| h, "greater than checks against false are unnecessary")),
182 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
183 "order comparisons between booleans can be simplified",
192 struct ExpressionInfoWithSpan {
193 one_side_is_unary_not: bool,
198 fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
200 if let ExprKind::Unary(unop, operand) = e.kind;
201 if let UnOp::UnNot = unop;
203 return (true, operand.span);
209 fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
210 let left = is_unary_not(left_side);
211 let right = is_unary_not(right_side);
213 ExpressionInfoWithSpan {
214 one_side_is_unary_not: left.0 != right.0,
220 fn check_comparison<'a, 'tcx>(
221 cx: &LateContext<'tcx>,
223 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
224 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
225 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
226 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
227 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
229 use self::Expression::{Bool, Other};
231 if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
233 cx.typeck_results().expr_ty(left_side),
234 cx.typeck_results().expr_ty(right_side),
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 = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
304 "try simplifying it as shown",
305 conv_hint(hint).to_string(),
316 fn fetch_bool_block(block: &Block<'_>) -> Expression {
317 match (&*block.stmts, block.expr.as_ref()) {
318 (&[], Some(e)) => fetch_bool_expr(&**e),
319 (&[ref e], None) => {
320 if let StmtKind::Semi(ref e) = e.kind {
321 if let ExprKind::Ret(_) = e.kind {
322 fetch_bool_expr(&**e)
330 _ => Expression::Other,
334 fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
336 ExprKind::Block(ref block, _) => fetch_bool_block(block),
337 ExprKind::Lit(ref lit_ptr) => {
338 if let LitKind::Bool(value) = lit_ptr.node {
339 Expression::Bool(value)
344 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
345 Expression::Bool(value) => Expression::RetBool(value),
346 _ => Expression::Other,
348 _ => Expression::Other,