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 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 #[derive(Copy, Clone)]
58 pub struct NeedlessBool;
60 impl LintPass for NeedlessBool {
61 fn get_lints(&self) -> LintArray {
62 lint_array!(NEEDLESS_BOOL)
65 fn name(&self) -> &'static str {
70 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
71 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
72 use self::Expression::*;
73 if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.node {
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.node {
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 fn parent_node_is_if_expr<'a, 'b>(expr: &Expr, cx: &LateContext<'a, 'b>) -> bool {
129 let parent_id = cx.tcx.hir().get_parent_node_by_hir_id(expr.hir_id);
130 let parent_node = cx.tcx.hir().get_by_hir_id(parent_id);
132 if let rustc::hir::Node::Expr(e) = parent_node {
133 if let ExprKind::If(_, _, _) = e.node {
141 #[derive(Copy, Clone)]
142 pub struct BoolComparison;
144 impl LintPass for BoolComparison {
145 fn get_lints(&self) -> LintArray {
146 lint_array!(BOOL_COMPARISON)
149 fn name(&self) -> &'static str {
154 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
155 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
156 if in_macro(e.span) {
160 if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
161 let ignore_case = None::<(fn(_) -> _, &str)>;
162 let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
165 let true_case = Some((|h| h, "equality checks against true are unnecessary"));
166 let false_case = Some((
168 "equality checks against false can be replaced by a negation",
170 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
173 let true_case = Some((
175 "inequality checks against true can be replaced by a negation",
177 let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
178 check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
180 BinOpKind::Lt => check_comparison(
184 Some((|h| h, "greater than checks against false are unnecessary")),
187 "less than comparison against true can be replaced by a negation",
191 |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
192 "order comparisons between booleans can be simplified",
195 BinOpKind::Gt => check_comparison(
200 "less than comparison against true can be replaced by a negation",
204 Some((|h| h, "greater than checks against false are unnecessary")),
206 |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
207 "order comparisons between booleans can be simplified",
216 fn check_comparison<'a, 'tcx>(
217 cx: &LateContext<'a, 'tcx>,
219 left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
220 left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
221 right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
222 right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
223 no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
225 use self::Expression::*;
227 if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
228 let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
229 if l_ty.is_bool() && r_ty.is_bool() {
230 let mut applicability = Applicability::MachineApplicable;
231 match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
232 (Bool(true), Other) => left_true.map_or((), |(h, m)| {
233 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
235 (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
236 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
238 (Bool(false), Other) => left_false.map_or((), |(h, m)| {
239 suggest_bool_comparison(cx, e, right_side, applicability, m, h)
241 (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
242 suggest_bool_comparison(cx, e, left_side, applicability, m, h)
244 (Other, Other) => no_literal.map_or((), |(h, m)| {
245 let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
246 let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
252 "try simplifying it as shown",
253 h(left_side, right_side).to_string(),
263 fn suggest_bool_comparison<'a, 'tcx>(
264 cx: &LateContext<'a, 'tcx>,
267 mut applicability: Applicability,
269 conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
271 let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
277 "try simplifying it as shown",
278 conv_hint(hint).to_string(),
289 fn fetch_bool_block(block: &Block) -> Expression {
290 match (&*block.stmts, block.expr.as_ref()) {
291 (&[], Some(e)) => fetch_bool_expr(&**e),
292 (&[ref e], None) => {
293 if let StmtKind::Semi(ref e) = e.node {
294 if let ExprKind::Ret(_) = e.node {
295 fetch_bool_expr(&**e)
303 _ => Expression::Other,
307 fn fetch_bool_expr(expr: &Expr) -> Expression {
309 ExprKind::Block(ref block, _) => fetch_bool_block(block),
310 ExprKind::Lit(ref lit_ptr) => {
311 if let LitKind::Bool(value) = lit_ptr.node {
312 Expression::Bool(value)
317 ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
318 Expression::Bool(value) => Expression::RetBool(value),
319 _ => Expression::Other,
321 _ => Expression::Other,