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 {
19 /// (or vice versa) and suggest 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<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
72 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
73 use self::Expression::{Bool, RetBool};
74 if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
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 parent_node_is_if_expr(&e, &cx) {
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(ref 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<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
132 fn check_expr(&mut self, cx: &LateContext<'a, '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) {
201 if let ExprKind::Unary(unop, operand) = e.kind;
202 if let UnOp::UnNot = unop;
204 return (true, operand.span);
210 fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
211 let left = is_unary_not(left_side);
212 let right = is_unary_not(right_side);
214 ExpressionInfoWithSpan {
215 one_side_is_unary_not: left.0 != right.0,
221 fn check_comparison<'a, 'tcx>(
222 cx: &LateContext<'a, 'tcx>,
224 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
225 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
226 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
227 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
228 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
230 use self::Expression::{Bool, Other};
232 if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
233 let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
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<'a, 'tcx>,
292 mut applicability: Applicability,
294 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
296 let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
302 "try simplifying it as shown",
303 conv_hint(hint).to_string(),
314 fn fetch_bool_block(block: &Block<'_>) -> Expression {
315 match (&*block.stmts, block.expr.as_ref()) {
316 (&[], Some(e)) => fetch_bool_expr(&**e),
317 (&[ref e], None) => {
318 if let StmtKind::Semi(ref e) = e.kind {
319 if let ExprKind::Ret(_) = e.kind {
320 fetch_bool_expr(&**e)
328 _ => Expression::Other,
332 fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
334 ExprKind::Block(ref block, _) => fetch_bool_block(block),
335 ExprKind::Lit(ref lit_ptr) => {
336 if let LitKind::Bool(value) = lit_ptr.node {
337 Expression::Bool(value)
342 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
343 Expression::Bool(value) => Expression::RetBool(value),
344 _ => Expression::Other,
346 _ => Expression::Other,