rust/clippy_lints/src/needless_bool.rs

379 lines
13 KiB
Rust

//! Checks for needless boolean results of if-else expressions
//!
//! This lint is **warn** by default
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
use clippy_utils::higher;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::sugg::Sugg;
use clippy_utils::{get_parent_node, is_else_clause, is_expn_of, peel_blocks, peel_blocks_with_stmt};
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, Node, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
use rustc_span::Span;
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
/// 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
/// # let x = true;
/// if x {
/// false
/// } else {
/// true
/// }
/// # ;
/// ```
///
/// Use instead:
/// ```rust
/// # let x = true;
/// !x
/// # ;
/// ```
#[clippy::version = "pre 1.29.0"]
pub NEEDLESS_BOOL,
complexity,
"if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
}
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.
///
/// ### Example
/// ```rust,ignore
/// if x == true {}
/// if y == false {}
/// ```
/// use `x` directly:
/// ```rust,ignore
/// if x {}
/// if !y {}
/// ```
#[clippy::version = "pre 1.29.0"]
pub BOOL_COMPARISON,
complexity,
"comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
}
declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
fn condition_needs_parentheses(e: &Expr<'_>) -> bool {
let mut inner = e;
while let ExprKind::Binary(_, i, _)
| ExprKind::Call(i, _)
| ExprKind::Cast(i, _)
| ExprKind::Type(i, _)
| ExprKind::Index(i, _) = inner.kind
{
if matches!(
i.kind,
ExprKind::Block(..)
| ExprKind::ConstBlock(..)
| ExprKind::If(..)
| ExprKind::Loop(..)
| ExprKind::Match(..)
) {
return true;
}
inner = i;
}
false
}
fn is_parent_stmt(cx: &LateContext<'_>, id: HirId) -> bool {
matches!(
get_parent_node(cx.tcx, id),
Some(Node::Stmt(..) | Node::Block(Block { stmts: &[], .. }))
)
}
impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
use self::Expression::{Bool, RetBool};
if e.span.from_expansion() {
return;
}
if let Some(higher::If {
cond,
then,
r#else: Some(r#else),
}) = higher::If::hir(e)
{
let reduce = |ret, not| {
let mut applicability = Applicability::MachineApplicable;
let snip = Sugg::hir_with_applicability(cx, cond, "<predicate>", &mut applicability);
let mut snip = if not { !snip } else { snip };
if ret {
snip = snip.make_return();
}
if is_else_clause(cx.tcx, e) {
snip = snip.blockify();
}
if condition_needs_parentheses(cond) && is_parent_stmt(cx, e.hir_id) {
snip = snip.maybe_par();
}
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,
);
};
if let Some((a, b)) = fetch_bool_block(then).and_then(|a| Some((a, fetch_bool_block(r#else)?))) {
match (a, b) {
(RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
span_lint(
cx,
NEEDLESS_BOOL,
e.span,
"this if-then-else expression will always return true",
);
},
(RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
span_lint(
cx,
NEEDLESS_BOOL,
e.span,
"this if-then-else expression will always return false",
);
},
(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),
_ => (),
}
}
}
}
}
declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
impl<'tcx> LateLintPass<'tcx> for BoolComparison {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
if e.span.from_expansion() {
return;
}
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<'tcx>| !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<'tcx>| !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<'tcx>| !h,
"less than comparison against true can be replaced by a negation",
)),
ignore_case,
Some((
|l: Sugg<'tcx>, r: Sugg<'tcx>| (!l).bit_and(&r),
"order comparisons between booleans can be simplified",
)),
),
BinOpKind::Gt => check_comparison(
cx,
e,
Some((
|h: Sugg<'tcx>| !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<'tcx>, r: Sugg<'tcx>| l.bit_and(&(!r)),
"order comparisons between booleans can be simplified",
)),
),
_ => (),
}
}
}
}
struct ExpressionInfoWithSpan {
one_side_is_unary_not: bool,
left_span: Span,
right_span: Span,
}
fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
if let ExprKind::Unary(UnOp::Not, operand) = e.kind {
return (true, operand.span);
}
(false, e.span)
}
fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
let left = is_unary_not(left_side);
let right = is_unary_not(right_side);
ExpressionInfoWithSpan {
one_side_is_unary_not: left.0 != right.0,
left_span: left.1,
right_span: right.1,
}
}
fn check_comparison<'a, 'tcx>(
cx: &LateContext<'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)>,
) {
if let ExprKind::Binary(op, left_side, right_side) = e.kind {
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;
if op.node == BinOpKind::Eq {
let expression_info = one_side_is_unary_not(left_side, right_side);
if expression_info.one_side_is_unary_not {
span_lint_and_sugg(
cx,
BOOL_COMPARISON,
e.span,
"this comparison might be written more concisely",
"try simplifying it as shown",
format!(
"{} != {}",
snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
),
applicability,
);
}
}
match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
(Some(true), None) => left_true.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, right_side, applicability, m, h);
}),
(None, Some(true)) => right_true.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, left_side, applicability, m, h);
}),
(Some(false), None) => left_false.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, right_side, applicability, m, h);
}),
(None, Some(false)) => right_false.map_or((), |(h, m)| {
suggest_bool_comparison(cx, e, left_side, applicability, m, h);
}),
(None, None) => 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>,
e: &'tcx Expr<'_>,
expr: &Expr<'_>,
mut app: Applicability,
message: &str,
conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
) {
let hint = Sugg::hir_with_context(cx, expr, e.span.ctxt(), "..", &mut app);
span_lint_and_sugg(
cx,
BOOL_COMPARISON,
e.span,
message,
"try simplifying it as shown",
conv_hint(hint).to_string(),
app,
);
}
enum Expression {
Bool(bool),
RetBool(bool),
}
fn fetch_bool_block(expr: &Expr<'_>) -> Option<Expression> {
match peel_blocks_with_stmt(expr).kind {
ExprKind::Ret(Some(ret)) => Some(Expression::RetBool(fetch_bool_expr(ret)?)),
_ => Some(Expression::Bool(fetch_bool_expr(expr)?)),
}
}
fn fetch_bool_expr(expr: &Expr<'_>) -> Option<bool> {
if let ExprKind::Lit(ref lit_ptr) = peel_blocks(expr).kind {
if let LitKind::Bool(value) = lit_ptr.node {
return Some(value);
}
}
None
}