rust/clippy_lints/src/temporary_assignment.rs
2018-03-28 15:24:26 +02:00

52 lines
1.4 KiB
Rust

use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::hir::{Expr, ExprAssign, ExprField, ExprStruct, ExprTup, ExprTupField};
use utils::is_adjusted;
use utils::span_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
/// ```
declare_clippy_lint! {
pub TEMPORARY_ASSIGNMENT,
complexity,
"assignments to temporaries"
}
fn is_temporary(expr: &Expr) -> bool {
match expr.node {
ExprStruct(..) | ExprTup(..) => true,
_ => false,
}
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(TEMPORARY_ASSIGNMENT)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let ExprAssign(ref target, _) = expr.node {
match target.node {
ExprField(ref base, _) | ExprTupField(ref base, _) => if is_temporary(base) && !is_adjusted(cx, base) {
span_lint(cx, TEMPORARY_ASSIGNMENT, expr.span, "assignment to temporary");
},
_ => (),
}
}
}
}