1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
10 //! Checks for needless boolean results of if-else expressions
12 //! This lint is **warn** by default
14 use crate::utils::sugg::Sugg;
15 use crate::utils::{in_macro, span_lint, span_lint_and_sugg};
17 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
18 use rustc::{declare_tool_lint, lint_array};
19 use rustc_errors::Applicability;
20 use syntax::ast::LitKind;
21 use syntax::source_map::Spanned;
23 /// **What it does:** Checks for expressions of the form `if c { true } else {
25 /// (or vice versa) and suggest using the condition directly.
27 /// **Why is this bad?** Redundant code.
29 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
30 /// painstakingly documented (which we of course do not detect), so they *may*
31 /// have some value. Even then, the documentation can be rewritten to match the
42 declare_clippy_lint! {
45 "if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`"
48 /// **What it does:** Checks for expressions of the form `x == true`,
49 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
50 /// suggest using the variable directly.
52 /// **Why is this bad?** Unnecessary code.
54 /// **Known problems:** None.
58 /// if x == true {} // could be `if x { }`
60 declare_clippy_lint! {
63 "comparing a variable to a boolean, e.g. `if x == true` or `if x != true`"
66 #[derive(Copy, Clone)]
67 pub struct NeedlessBool;
69 impl LintPass for NeedlessBool {
70 fn get_lints(&self) -> LintArray {
71 lint_array!(NEEDLESS_BOOL)
75 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
76 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
77 use self::Expression::*;
78 if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.node {
79 let reduce = |ret, not| {
80 let mut applicability = Applicability::MachineApplicable;
81 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
82 let snip = if not { !snip } else { snip };
85 format!("return {}", snip)
94 "this if-then-else expression returns a bool literal",
95 "you can reduce it to",
100 if let ExprKind::Block(ref then_block, _) = then_block.node {
101 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
102 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
107 "this if-then-else expression will always return true",
110 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
115 "this if-then-else expression will always return false",
118 (RetBool(true), RetBool(false)) => reduce(true, false),
119 (Bool(true), Bool(false)) => reduce(false, false),
120 (RetBool(false), RetBool(true)) => reduce(true, true),
121 (Bool(false), Bool(true)) => reduce(false, true),
125 panic!("IfExpr 'then' node is not an ExprKind::Block");
131 #[derive(Copy, Clone)]
132 pub struct BoolComparison;
134 impl LintPass for BoolComparison {
135 fn get_lints(&self) -> LintArray {
136 lint_array!(BOOL_COMPARISON)
140 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
141 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
142 if in_macro(e.span) {
146 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
147 let ignore_case = None::<(fn(_) -> _, &str)>;
148 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
151 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
152 let false_case = Some((
154 "equality checks against false can be replaced by a negation",
156 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
159 let true_case = Some((
161 "inequality checks against true can be replaced by a negation",
163 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
164 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
166 BinOpKind::Lt => check_comparison(
170 Some((|h| h, "greater than checks against false are unnecessary")),
173 "less than comparison against true can be replaced by a negation",
177 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
178 "order comparisons between booleans can be simplified",
181 BinOpKind::Gt => check_comparison(
186 "less than comparison against true can be replaced by a negation",
190 Some((|h| h, "greater than checks against false are unnecessary")),
192 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
193 "order comparisons between booleans can be simplified",
202 fn check_comparison<'a, 'tcx>(
203 cx: &LateContext<'a, 'tcx>,
205 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
206 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
207 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
208 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
209 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
211 use self::Expression::*;
213 if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
214 let mut applicability = Applicability::MachineApplicable;
215 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
216 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
217 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
219 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
220 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
222 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
223 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
225 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
226 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
228 (Other, Other) => no_literal.map_or((), |(h, m)| {
229 let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
230 if l_ty.is_bool() && r_ty.is_bool() {
231 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
232 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
238 "try simplifying it as shown",
239 h(left_side, right_side).to_string(),
249 fn suggest_bool_comparison<'a, 'tcx>(
250 cx: &LateContext<'a, 'tcx>,
253 mut applicability: Applicability,
255 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
257 let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
263 "try simplifying it as shown",
264 conv_hint(hint).to_string(),
275 fn fetch_bool_block(block: &Block) -> Expression {
276 match (&*block.stmts, block.expr.as_ref()) {
277 (&[], Some(e)) => fetch_bool_expr(&**e),
278 (&[ref e], None) => {
279 if let StmtKind::Semi(ref e, _) = e.node {
280 if let ExprKind::Ret(_) = e.node {
281 fetch_bool_expr(&**e)
289 _ => Expression::Other,
293 fn fetch_bool_expr(expr: &Expr) -> Expression {
295 ExprKind::Block(ref block, _) => fetch_bool_block(block),
296 ExprKind::Lit(ref lit_ptr) => {
297 if let LitKind::Bool(value) = lit_ptr.node {
298 Expression::Bool(value)
303 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
304 Expression::Bool(value) => Expression::RetBool(value),
305 _ => Expression::Other,
307 _ => Expression::Other,