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use crate::{make, Lint, Metadata, Report, Rule, Suggestion};
use if_chain::if_chain;
use macros::lint;
use rnix::{
types::{BinOp, BinOpKind, Ident, TokenWrapper, TypedNode},
NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode,
};
#[lint(
name = "bool_comparison",
note = "Unnecessary comparison with boolean",
match_with = SyntaxKind::NODE_BIN_OP
)]
struct BoolComparison;
impl Rule for BoolComparison {
fn validate(&self, node: &SyntaxElement) -> Option<Report> {
if_chain! {
if let NodeOrToken::Node(bin_op_node) = node;
if let Some(bin_expr) = BinOp::cast(bin_op_node.clone());
if let Some(lhs) = bin_expr.lhs();
if let Some(rhs) = bin_expr.rhs();
if let op@(BinOpKind::Equal | BinOpKind::NotEqual) = bin_expr.operator();
let (non_bool_side, bool_side) = if boolean_ident(&lhs).is_some() {
(rhs, lhs)
} else if boolean_ident(&rhs).is_some() {
(lhs, rhs)
} else {
return None
};
then {
let at = node.text_range();
let replacement = {
match (boolean_ident(&bool_side).unwrap(), op == BinOpKind::Equal) {
(NixBoolean::True, true) | (NixBoolean::False, false) => {
// `a == true`, `a != false` replace with just `a`
non_bool_side.clone()
},
(NixBoolean::True, false) | (NixBoolean::False, true) => {
// `a != true`, `a == false` replace with `!a`
match non_bool_side.kind() {
SyntaxKind::NODE_APPLY
| SyntaxKind::NODE_PAREN
| SyntaxKind::NODE_IDENT => {
// do not parenthsize the replacement
make::unary_not(&non_bool_side).node().clone()
},
SyntaxKind::NODE_BIN_OP => {
let inner = BinOp::cast(non_bool_side.clone()).unwrap();
// `!a ? b`, no paren required
if inner.operator() == BinOpKind::IsSet {
make::unary_not(&non_bool_side).node().clone()
} else {
let parens = make::parenthesize(&non_bool_side);
make::unary_not(parens.node()).node().clone()
}
},
_ => {
let parens = make::parenthesize(&non_bool_side);
make::unary_not(parens.node()).node().clone()
}
}
},
}
};
let message = format!(
"Comparing `{}` with boolean literal `{}`",
non_bool_side,
bool_side
);
Some(
Report::new(Self::note())
.suggest(at, message, Suggestion::new(at, replacement))
)
} else {
None
}
}
}
}
enum NixBoolean {
True,
False,
}
// not entirely accurate, underhanded nix programmers might write `true = false`
fn boolean_ident(node: &SyntaxNode) -> Option<NixBoolean> {
Ident::cast(node.clone())
.map(|ident_expr| match ident_expr.as_str() {
"true" => Some(NixBoolean::True),
"false" => Some(NixBoolean::False),
_ => None,
})
.flatten()
}
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