Update upstream source from tag 'upstream/1.52.1+dfsg1'

[rustc.git] / src / tools / clippy / clippy_lints / src / methods / iter_nth.rs

diff --git a/src/tools/clippy/clippy_lints/src/methods/iter_nth.rs b/src/tools/clippy/clippy_lints/src/methods/iter_nth.rs
new file mode 100644 (file)
index 0000000..cc3e56e
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/iter_nth.rs
@@ -0,0 +1,38 @@
+use crate::methods::derefs_to_slice;
+use crate::methods::iter_nth_zero;
+use crate::utils::{is_type_diagnostic_item, span_lint_and_help};
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_span::symbol::sym;
+
+use super::ITER_NTH;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &hir::Expr<'_>,
+    nth_and_iter_args: &[&'tcx [hir::Expr<'tcx>]],
+    is_mut: bool,
+) {
+    let iter_args = nth_and_iter_args[1];
+    let mut_str = if is_mut { "_mut" } else { "" };
+    let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.typeck_results().expr_ty(&iter_args[0])).is_some() {
+        "slice"
+    } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym::vec_type) {
+        "Vec"
+    } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym::vecdeque_type) {
+        "VecDeque"
+    } else {
+        let nth_args = nth_and_iter_args[0];
+        iter_nth_zero::check(cx, expr, &nth_args);
+        return; // caller is not a type that we want to lint
+    };
+
+    span_lint_and_help(
+        cx,
+        ITER_NTH,
+        expr.span,
+        &format!("called `.iter{0}().nth()` on a {1}", mut_str, caller_type),
+        None,
+        &format!("calling `.get{}()` is both faster and more readable", mut_str),
+    );
+}