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|
//! Helper functions for extending the compiler with more linter-like
//! functionality while compiling (i.e. smarter warnings).
use super::*;
use ast::Expr;
/// Optimise the given expression where possible.
pub(super) fn optimise_expr(c: &mut Compiler, slot: LocalIdx, expr: ast::Expr) -> ast::Expr {
match expr {
Expr::BinOp(_) => optimise_bin_op(c, slot, expr),
_ => expr.to_owned(),
}
}
enum LitBool {
Expr(Expr),
True(Expr),
False(Expr),
}
/// Is this a literal boolean, or something else?
fn is_lit_bool(expr: ast::Expr) -> LitBool {
if let ast::Expr::Ident(ident) = &expr {
match ident.ident_token().unwrap().text() {
"true" => LitBool::True(expr),
"false" => LitBool::False(expr),
_ => LitBool::Expr(expr),
}
} else {
LitBool::Expr(expr)
}
}
/// Detect useless binary operations (i.e. useless bool comparisons).
fn optimise_bin_op(c: &mut Compiler, slot: LocalIdx, expr: ast::Expr) -> ast::Expr {
use ast::BinOpKind;
// bail out of this check if the user has overridden either `true`
// or `false` identifiers. Note that they will have received a
// separate warning about this for shadowing the global(s).
if c.is_user_defined("true") || c.is_user_defined("false") {
return expr;
}
if let Expr::BinOp(op) = &expr {
let lhs = is_lit_bool(op.lhs().unwrap());
let rhs = is_lit_bool(op.rhs().unwrap());
match (op.operator().unwrap(), lhs, rhs) {
// useless `false` arm in `||` expression
(BinOpKind::Or, LitBool::False(f), LitBool::Expr(other))
| (BinOpKind::Or, LitBool::Expr(other), LitBool::False(f)) => {
c.emit_warning(
&f,
WarningKind::UselessBoolOperation(
"this `false` has no effect on the result of the comparison",
),
);
return other;
}
// useless `true` arm in `&&` expression
(BinOpKind::And, LitBool::True(t), LitBool::Expr(other))
| (BinOpKind::And, LitBool::Expr(other), LitBool::True(t)) => {
c.emit_warning(
&t,
WarningKind::UselessBoolOperation(
"this `true` has no effect on the result of the comparison",
),
);
return other;
}
// useless `||` expression (one arm is `true`), return
// `true` directly (and warn about dead code on the right)
(BinOpKind::Or, LitBool::True(t), LitBool::Expr(other)) => {
c.emit_warning(
op,
WarningKind::UselessBoolOperation("this expression is always true"),
);
c.compile_dead_code(slot, other);
return t;
}
(BinOpKind::Or, _, LitBool::True(t)) | (BinOpKind::Or, LitBool::True(t), _) => {
c.emit_warning(
op,
WarningKind::UselessBoolOperation("this expression is always true"),
);
return t;
}
// useless `&&` expression (one arm is `false), same as above
(BinOpKind::And, LitBool::False(f), LitBool::Expr(other)) => {
c.emit_warning(
op,
WarningKind::UselessBoolOperation("this expression is always false"),
);
c.compile_dead_code(slot, other);
return f;
}
(BinOpKind::And, _, LitBool::False(f)) | (BinOpKind::Or, LitBool::False(f), _) => {
c.emit_warning(
op,
WarningKind::UselessBoolOperation("this expression is always false"),
);
return f;
}
_ => { /* nothing to optimise */ }
}
}
expr
}
|
