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::{
higher, is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg,
};
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use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
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use rustc_span::Span;
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declare_clippy_lint! {
/// **What it does:** Checks for expressions of the form `if c { true } else {
/// false }` (or vice versa) and suggests using the condition directly.
///
/// **Why is this bad?** Redundant code.
///
/// **Known problems:** Maybe false positives: Sometimes, the two branches are
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/// 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.
///
/// **Example:**
/// ```rust,ignore
/// if x {
/// false
/// } else {
/// true
/// }
/// ```
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/// Could be written as
/// ```rust,ignore
/// !x
/// ```
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pub NEEDLESS_BOOL,
complexity,
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"if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
}
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declare_clippy_lint! {
/// **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,ignore
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/// if x == true {}
/// if y == false {}
/// ```
/// use `x` directly:
/// ```rust,ignore
/// if x {}
/// if !y {}
/// ```
pub BOOL_COMPARISON,
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complexity,
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"comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
}
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declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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use self::Expression::{Bool, RetBool};
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if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
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let reduce = |ret, not| {
let mut applicability = Applicability::MachineApplicable;
let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
let mut snip = if not { !snip } else { snip };
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if ret {
snip = snip.make_return();
}
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if parent_node_is_if_expr(&e, &cx) {
snip = snip.blockify()
}
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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",
snip.to_string(),
applicability,
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);
};
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if let ExprKind::Block(ref then_block, _) = then_block.kind {
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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`");
}
}
}
}
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declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
impl<'tcx> LateLintPass<'tcx> for BoolComparison {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if e.span.from_expansion() {
return;
}
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if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
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",
)),
),
_ => (),
}
}
}
}
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struct ExpressionInfoWithSpan {
one_side_is_unary_not: bool,
left_span: Span,
right_span: Span,
}
fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
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if let ExprKind::Unary(UnOp::UnNot, operand) = e.kind {
return (true, operand.span);
}
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(false, e.span)
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}
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fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
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let left = is_unary_not(left_side);
let right = is_unary_not(right_side);
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ExpressionInfoWithSpan {
one_side_is_unary_not: left.0 != right.0,
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left_span: left.1,
right_span: right.1,
}
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}
fn check_comparison<'a, 'tcx>(
cx: &LateContext<'tcx>,
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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)>,
) {
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use self::Expression::{Bool, Other};
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if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
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let (l_ty, r_ty) = (
cx.typeck_results().expr_ty(left_side),
cx.typeck_results().expr_ty(right_side),
);
if is_expn_of(left_side.span, "cfg").is_some() || is_expn_of(right_side.span, "cfg").is_some() {
return;
}
if l_ty.is_bool() && r_ty.is_bool() {
let mut applicability = Applicability::MachineApplicable;
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if let BinOpKind::Eq = op.node {
let expression_info = one_side_is_unary_not(&left_side, &right_side);
if expression_info.one_side_is_unary_not {
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span_lint_and_sugg(
cx,
BOOL_COMPARISON,
e.span,
"this comparison might be written more concisely",
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"try simplifying it as shown",
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format!(
"{} != {}",
snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
),
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applicability,
)
}
}
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 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<'tcx>,
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e: &'tcx Expr<'_>,
expr: &Expr<'_>,
mut applicability: Applicability,
message: &str,
conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
) {
let hint = if expr.span.from_expansion() {
if applicability != Applicability::Unspecified {
applicability = Applicability::MaybeIncorrect;
}
Sugg::hir_with_macro_callsite(cx, expr, "..")
} else {
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,
}
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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) => {
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if let StmtKind::Semi(ref e) = e.kind {
if let ExprKind::Ret(_) = e.kind {
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fetch_bool_expr(&**e)
} else {
Expression::Other
}
} else {
Expression::Other
}
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},
_ => Expression::Other,
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}
}
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fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
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match expr.kind {
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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,
}
}