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use clippy_utils::diagnostics::span_lint;
use clippy_utils::is_adjusted;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// **What it does:** Checks for construction of a structure or tuple just to
/// assign a value in it.
///
/// **Why is this bad?** Readability. If the structure is only created to be
/// updated, why not write the structure you want in the first place?
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// (0, 0).0 = 1
/// ```
pub TEMPORARY_ASSIGNMENT,
complexity,
"assignments to temporaries"
}
fn is_temporary(expr: &Expr<'_>) -> bool {
matches!(&expr.kind, ExprKind::Struct(..) | ExprKind::Tup(..))
}
declare_lint_pass!(TemporaryAssignment => [TEMPORARY_ASSIGNMENT]);
impl<'tcx> LateLintPass<'tcx> for TemporaryAssignment {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Assign(target, ..) = &expr.kind {
let mut base = target;
while let ExprKind::Field(f, _) | ExprKind::Index(f, _) = &base.kind {
base = f;
}
if is_temporary(base) && !is_adjusted(cx, base) {
span_lint(cx, TEMPORARY_ASSIGNMENT, expr.span, "assignment to temporary");
}
}
}
}
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