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::{in_macro, span_lint, span_lint_and_sugg};
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
9 use rustc::{declare_tool_lint, lint_array};
10 use rustc_errors::Applicability;
11 use syntax::ast::LitKind;
12 use syntax::source_map::Spanned;
14 /// **What it does:** Checks for expressions of the form `if c { true } else {
16 /// (or vice versa) and suggest using the condition directly.
18 /// **Why is this bad?** Redundant code.
20 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
21 /// painstakingly documented (which we of course do not detect), so they *may*
22 /// have some value. Even then, the documentation can be rewritten to match the
33 declare_clippy_lint! {
36 "if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`"
39 /// **What it does:** Checks for expressions of the form `x == true`,
40 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
41 /// suggest using the variable directly.
43 /// **Why is this bad?** Unnecessary code.
45 /// **Known problems:** None.
49 /// if x == true {} // could be `if x { }`
51 declare_clippy_lint! {
54 "comparing a variable to a boolean, e.g. `if x == true` or `if x != true`"
57 #[derive(Copy, Clone)]
58 pub struct NeedlessBool;
60 impl LintPass for NeedlessBool {
61 fn get_lints(&self) -> LintArray {
62 lint_array!(NEEDLESS_BOOL)
66 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
67 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
68 use self::Expression::*;
69 if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.node {
70 let reduce = |ret, not| {
71 let mut applicability = Applicability::MachineApplicable;
72 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
73 let snip = if not { !snip } else { snip };
76 format!("return {}", snip)
85 "this if-then-else expression returns a bool literal",
86 "you can reduce it to",
91 if let ExprKind::Block(ref then_block, _) = then_block.node {
92 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
93 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
98 "this if-then-else expression will always return true",
101 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
106 "this if-then-else expression will always return false",
109 (RetBool(true), RetBool(false)) => reduce(true, false),
110 (Bool(true), Bool(false)) => reduce(false, false),
111 (RetBool(false), RetBool(true)) => reduce(true, true),
112 (Bool(false), Bool(true)) => reduce(false, true),
116 panic!("IfExpr 'then' node is not an ExprKind::Block");
122 #[derive(Copy, Clone)]
123 pub struct BoolComparison;
125 impl LintPass for BoolComparison {
126 fn get_lints(&self) -> LintArray {
127 lint_array!(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 in_macro(e.span) {
137 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
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 fn check_comparison<'a, 'tcx>(
194 cx: &LateContext<'a, 'tcx>,
196 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
197 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
198 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
199 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
200 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
202 use self::Expression::*;
204 if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
205 let mut applicability = Applicability::MachineApplicable;
206 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
207 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
208 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
210 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
211 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
213 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
214 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
216 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
217 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
219 (Other, Other) => no_literal.map_or((), |(h, m)| {
220 let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
221 if l_ty.is_bool() && r_ty.is_bool() {
222 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
223 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
229 "try simplifying it as shown",
230 h(left_side, right_side).to_string(),
240 fn suggest_bool_comparison<'a, 'tcx>(
241 cx: &LateContext<'a, 'tcx>,
244 mut applicability: Applicability,
246 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
248 let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
254 "try simplifying it as shown",
255 conv_hint(hint).to_string(),
266 fn fetch_bool_block(block: &Block) -> Expression {
267 match (&*block.stmts, block.expr.as_ref()) {
268 (&[], Some(e)) => fetch_bool_expr(&**e),
269 (&[ref e], None) => {
270 if let StmtKind::Semi(ref e) = e.node {
271 if let ExprKind::Ret(_) = e.node {
272 fetch_bool_expr(&**e)
280 _ => Expression::Other,
284 fn fetch_bool_expr(expr: &Expr) -> Expression {
286 ExprKind::Block(ref block, _) => fetch_bool_block(block),
287 ExprKind::Lit(ref lit_ptr) => {
288 if let LitKind::Bool(value) = lit_ptr.node {
289 Expression::Bool(value)
294 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
295 Expression::Bool(value) => Expression::RetBool(value),
296 _ => Expression::Other,
298 _ => Expression::Other,