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, in_macro_or_desugar, span_lint, span_lint_and_sugg};
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
9 use rustc::{declare_lint_pass, declare_tool_lint};
10 use rustc_errors::Applicability;
11 use syntax::ast::LitKind;
12 use syntax::source_map::Spanned;
14 declare_clippy_lint! {
15 /// **What it does:** Checks for expressions of the form `if c { true } else {
17 /// (or vice versa) and suggest using the condition directly.
19 /// **Why is this bad?** Redundant code.
21 /// **Known problems:** Maybe false positives: Sometimes, the two branches are
22 /// painstakingly documented (which we, of course, do not detect), so they *may*
23 /// have some value. Even then, the documentation can be rewritten to match the
36 "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
39 declare_clippy_lint! {
40 /// **What it does:** Checks for expressions of the form `x == true`,
41 /// `x != true` and order comparisons such as `x < true` (or vice versa) and
42 /// suggest using the variable directly.
44 /// **Why is this bad?** Unnecessary code.
46 /// **Known problems:** None.
50 /// if x == true {} // could be `if x { }`
54 "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
57 declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
59 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
60 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
61 use self::Expression::*;
62 if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
63 let reduce = |ret, not| {
64 let mut applicability = Applicability::MachineApplicable;
65 let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
66 let mut snip = if not { !snip } else { snip };
69 snip = snip.make_return();
72 if parent_node_is_if_expr(&e, &cx) {
73 snip = snip.blockify()
80 "this if-then-else expression returns a bool literal",
81 "you can reduce it to",
86 if let ExprKind::Block(ref then_block, _) = then_block.node {
87 match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
88 (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
93 "this if-then-else expression will always return true",
96 (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
101 "this if-then-else expression will always return false",
104 (RetBool(true), RetBool(false)) => reduce(true, false),
105 (Bool(true), Bool(false)) => reduce(false, false),
106 (RetBool(false), RetBool(true)) => reduce(true, true),
107 (Bool(false), Bool(true)) => reduce(false, true),
111 panic!("IfExpr 'then' node is not an ExprKind::Block");
117 fn parent_node_is_if_expr<'a, 'b>(expr: &Expr, cx: &LateContext<'a, 'b>) -> bool {
118 let parent_id = cx.tcx.hir().get_parent_node(expr.hir_id);
119 let parent_node = cx.tcx.hir().get(parent_id);
122 rustc::hir::Node::Expr(e) => {
123 higher::if_block(&e).is_some()
125 rustc::hir::Node::Arm(e) => {
126 higher::if_block(&e.body).is_some()
132 declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
134 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
135 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
136 if in_macro_or_desugar(e.span) {
140 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
141 let ignore_case = None::<(fn(_) -> _, &str)>;
142 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
145 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
146 let false_case = Some((
148 "equality checks against false can be replaced by a negation",
150 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
153 let true_case = Some((
155 "inequality checks against true can be replaced by a negation",
157 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
158 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
160 BinOpKind::Lt => check_comparison(
164 Some((|h| h, "greater than checks against false are unnecessary")),
167 "less than comparison against true can be replaced by a negation",
171 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
172 "order comparisons between booleans can be simplified",
175 BinOpKind::Gt => check_comparison(
180 "less than comparison against true can be replaced by a negation",
184 Some((|h| h, "greater than checks against false are unnecessary")),
186 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
187 "order comparisons between booleans can be simplified",
196 fn check_comparison<'a, 'tcx>(
197 cx: &LateContext<'a, 'tcx>,
199 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
200 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
201 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
202 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
203 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
205 use self::Expression::*;
207 if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
208 let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
209 if l_ty.is_bool() && r_ty.is_bool() {
210 let mut applicability = Applicability::MachineApplicable;
211 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
212 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
213 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
215 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
216 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
218 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
219 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
221 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
222 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
224 (Other, Other) => no_literal.map_or((), |(h, m)| {
225 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
226 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
232 "try simplifying it as shown",
233 h(left_side, right_side).to_string(),
243 fn suggest_bool_comparison<'a, 'tcx>(
244 cx: &LateContext<'a, 'tcx>,
247 mut applicability: Applicability,
249 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
251 let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
257 "try simplifying it as shown",
258 conv_hint(hint).to_string(),
269 fn fetch_bool_block(block: &Block) -> Expression {
270 match (&*block.stmts, block.expr.as_ref()) {
271 (&[], Some(e)) => fetch_bool_expr(&**e),
272 (&[ref e], None) => {
273 if let StmtKind::Semi(ref e) = e.node {
274 if let ExprKind::Ret(_) = e.node {
275 fetch_bool_expr(&**e)
283 _ => Expression::Other,
287 fn fetch_bool_expr(expr: &Expr) -> Expression {
289 ExprKind::Block(ref block, _) => fetch_bool_block(block),
290 ExprKind::Lit(ref lit_ptr) => {
291 if let LitKind::Bool(value) = lit_ptr.node {
292 Expression::Bool(value)
297 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
298 Expression::Bool(value) => Expression::RetBool(value),
299 _ => Expression::Other,
301 _ => Expression::Other,