New upstream version 1.52.1+dfsg1

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

diff --git a/src/tools/clippy/clippy_lints/src/methods/flat_map_identity.rs b/src/tools/clippy/clippy_lints/src/methods/flat_map_identity.rs
new file mode 100644 (file)
index 0000000..ce3194f
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/flat_map_identity.rs
@@ -0,0 +1,57 @@
+use crate::utils::{match_qpath, match_trait_method, paths, span_lint_and_sugg};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_span::source_map::Span;
+
+use super::FLAT_MAP_IDENTITY;
+
+/// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx hir::Expr<'_>,
+    flat_map_args: &'tcx [hir::Expr<'_>],
+    flat_map_span: Span,
+) {
+    if match_trait_method(cx, expr, &paths::ITERATOR) {
+        let arg_node = &flat_map_args[1].kind;
+
+        let apply_lint = |message: &str| {
+            span_lint_and_sugg(
+                cx,
+                FLAT_MAP_IDENTITY,
+                flat_map_span.with_hi(expr.span.hi()),
+                message,
+                "try",
+                "flatten()".to_string(),
+                Applicability::MachineApplicable,
+            );
+        };
+
+        if_chain! {
+            if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
+            let body = cx.tcx.hir().body(*body_id);
+
+            if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
+            if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
+
+            if path.segments.len() == 1;
+            if path.segments[0].ident.name == binding_ident.name;
+
+            then {
+                apply_lint("called `flat_map(|x| x)` on an `Iterator`");
+            }
+        }
+
+        if_chain! {
+            if let hir::ExprKind::Path(ref qpath) = arg_node;
+
+            if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
+
+            then {
+                apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
+            }
+        }
+    }
+}