rust-clippy/clippy_lints/src/needless_bool.rs

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//! Checks for needless boolean results of if-else expressions
//!
//! This lint is **warn** by default
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use crate::utils::sugg::Sugg;
use crate::utils::{in_macro, span_lint, span_lint_and_sugg};
use rustc::hir::*;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_tool_lint, lint_array};
use rustc_errors::Applicability;
use syntax::ast::LitKind;
use syntax::source_map::Spanned;
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/// **What it does:** Checks for expressions of the form `if c { true } else {
/// false }`
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/// (or vice versa) and suggest using the condition directly.
///
/// **Why is this bad?** Redundant code.
///
/// **Known problems:** Maybe false positives: Sometimes, the two branches are
/// painstakingly documented (which we of course do not detect), so they *may*
/// have some value. Even then, the documentation can be rewritten to match the
/// shorter code.
///
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/// **Example:**
/// ```rust
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/// if x {
/// false
/// } else {
/// true
/// }
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/// ```
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declare_clippy_lint! {
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pub NEEDLESS_BOOL,
complexity,
"if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`"
}
/// **What it does:** Checks for expressions of the form `x == true`,
/// `x != true` and order comparisons such as `x < true` (or vice versa) and
/// suggest using the variable directly.
///
/// **Why is this bad?** Unnecessary code.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
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/// if x == true {} // could be `if x { }`
/// ```
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declare_clippy_lint! {
pub BOOL_COMPARISON,
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complexity,
"comparing a variable to a boolean, e.g. `if x == true` or `if x != true`"
}
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#[derive(Copy, Clone)]
pub struct NeedlessBool;
impl LintPass for NeedlessBool {
fn get_lints(&self) -> LintArray {
lint_array!(NEEDLESS_BOOL)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
use self::Expression::*;
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if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.node {
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let reduce = |ret, not| {
let mut applicability = Applicability::MachineApplicable;
let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
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let snip = if not { !snip } else { snip };
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let mut hint = if ret {
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format!("return {}", snip)
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} else {
snip.to_string()
};
if parent_node_is_if_expr(&e, &cx) {
hint = format!("{{ {} }}", hint);
}
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span_lint_and_sugg(
cx,
NEEDLESS_BOOL,
e.span,
"this if-then-else expression returns a bool literal",
"you can reduce it to",
hint,
applicability,
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);
};
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if let ExprKind::Block(ref then_block, _) = then_block.node {
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match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
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(RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
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span_lint(
cx,
NEEDLESS_BOOL,
e.span,
"this if-then-else expression will always return true",
);
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},
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(RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
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span_lint(
cx,
NEEDLESS_BOOL,
e.span,
"this if-then-else expression will always return false",
);
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},
(RetBool(true), RetBool(false)) => reduce(true, false),
(Bool(true), Bool(false)) => reduce(false, false),
(RetBool(false), RetBool(true)) => reduce(true, true),
(Bool(false), Bool(true)) => reduce(false, true),
_ => (),
}
} else {
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panic!("IfExpr 'then' node is not an ExprKind::Block");
}
}
}
}
fn parent_node_is_if_expr<'a, 'b>(expr: &Expr, cx: &LateContext<'a, 'b>) -> bool {
let parent_id = cx.tcx.hir().get_parent_node(expr.id);
let parent_node = cx.tcx.hir().get(parent_id);
if let rustc::hir::Node::Expr(e) = parent_node {
if let ExprKind::If(_,_,_) = e.node {
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return true;
}
}
false
}
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#[derive(Copy, Clone)]
pub struct BoolComparison;
impl LintPass for BoolComparison {
fn get_lints(&self) -> LintArray {
lint_array!(BOOL_COMPARISON)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
return;
}
if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
let ignore_case = None::<(fn(_) -> _, &str)>;
let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
match node {
BinOpKind::Eq => {
let true_case = Some((|h| h, "equality checks against true are unnecessary"));
let false_case = Some((
|h: Sugg<'_>| !h,
"equality checks against false can be replaced by a negation",
));
check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
},
BinOpKind::Ne => {
let true_case = Some((
|h: Sugg<'_>| !h,
"inequality checks against true can be replaced by a negation",
));
let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
},
BinOpKind::Lt => check_comparison(
cx,
e,
ignore_case,
Some((|h| h, "greater than checks against false are unnecessary")),
Some((
|h: Sugg<'_>| !h,
"less than comparison against true can be replaced by a negation",
)),
ignore_case,
Some((
|l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
"order comparisons between booleans can be simplified",
)),
),
BinOpKind::Gt => check_comparison(
cx,
e,
Some((
|h: Sugg<'_>| !h,
"less than comparison against true can be replaced by a negation",
)),
ignore_case,
ignore_case,
Some((|h| h, "greater than checks against false are unnecessary")),
Some((
|l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
"order comparisons between booleans can be simplified",
)),
),
_ => (),
}
}
}
}
fn check_comparison<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
e: &'tcx Expr,
left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
) {
use self::Expression::*;
if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
let mut applicability = Applicability::MachineApplicable;
match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
(Bool(true), Other) => left_true.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, right_side, applicability, m, h)
}),
(Other, Bool(true)) => right_true.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, left_side, applicability, m, h)
}),
(Bool(false), Other) => left_false.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, right_side, applicability, m, h)
}),
(Other, Bool(false)) => right_false.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, left_side, applicability, m, h)
}),
(Other, Other) => no_literal.map_or((), |(h, m)| {
let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
if l_ty.is_bool() && r_ty.is_bool() {
let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
span_lint_and_sugg(
cx,
BOOL_COMPARISON,
e.span,
m,
"try simplifying it as shown",
h(left_side, right_side).to_string(),
applicability,
)
}
}),
_ => (),
}
}
}
fn suggest_bool_comparison<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
e: &'tcx Expr,
expr: &Expr,
mut applicability: Applicability,
message: &str,
conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
) {
let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
span_lint_and_sugg(
cx,
BOOL_COMPARISON,
e.span,
message,
"try simplifying it as shown",
conv_hint(hint).to_string(),
applicability,
);
}
enum Expression {
Bool(bool),
RetBool(bool),
Other,
}
fn fetch_bool_block(block: &Block) -> Expression {
match (&*block.stmts, block.expr.as_ref()) {
(&[], Some(e)) => fetch_bool_expr(&**e),
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(&[ref e], None) => {
if let StmtKind::Semi(ref e, _) = e.node {
if let ExprKind::Ret(_) = e.node {
fetch_bool_expr(&**e)
} else {
Expression::Other
}
} else {
Expression::Other
}
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},
_ => Expression::Other,
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}
}
fn fetch_bool_expr(expr: &Expr) -> Expression {
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match expr.node {
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ExprKind::Block(ref block, _) => fetch_bool_block(block),
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ExprKind::Lit(ref lit_ptr) => {
if let LitKind::Bool(value) = lit_ptr.node {
Expression::Bool(value)
} else {
Expression::Other
}
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},
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ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
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Expression::Bool(value) => Expression::RetBool(value),
_ => Expression::Other,
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},
_ => Expression::Other,
}
}