From c20afbdfe017a904180f01499139adfafe296bbf Mon Sep 17 00:00:00 2001
From: Marcin Serwin <toxyxer@gmail.com>
Date: Wed, 15 Apr 2020 18:37:37 +0200
Subject: [PATCH 1/2] Lint map_flatten if caller is an Option
---
clippy_lints/src/methods/mod.rs | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 5255fec2cec..608b351c3e1 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -2484,7 +2484,7 @@ fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, ok_args: &[hir
}
}
-/// lint use of `map().flatten()` for `Iterators`
+/// lint use of `map().flatten()` for `Iterators` and 'Options'
fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>, map_args: &'tcx [hir::Expr<'_>]) {
// lint if caller of `.map().flatten()` is an Iterator
if match_trait_method(cx, expr, &paths::ITERATOR) {
@@ -2503,6 +2503,24 @@ fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<
Applicability::MachineApplicable,
);
}
+
+ // lint if caller of `.map().flatten()` is an Option
+ if match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION) {
+ let msg = "called `map(..).flatten()` on an `Option`. \
+ This is more succinctly expressed by calling `.and_then(..)`";
+ let self_snippet = snippet(cx, map_args[0].span, "..");
+ let func_snippet = snippet(cx, map_args[1].span, "..");
+ let hint = format!("{0}.and_then({1})", self_snippet, func_snippet);
+ span_lint_and_sugg(
+ cx,
+ MAP_FLATTEN,
+ expr.span,
+ msg,
+ "try using `and_then` instead",
+ hint,
+ Applicability::MachineApplicable,
+ );
+ }
}
/// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
From 72a8fc24e600c7a2b01799b824af8c9c8d67de1f Mon Sep 17 00:00:00 2001
From: Marcin Serwin <toxyxer@gmail.com>
Date: Wed, 15 Apr 2020 19:06:41 +0200
Subject: [PATCH 2/2] Add test to map_flatten with an Option
---
tests/ui/map_flatten.fixed | 1 +
tests/ui/map_flatten.rs | 1 +
tests/ui/map_flatten.stderr | 8 +++++++-
3 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/tests/ui/map_flatten.fixed b/tests/ui/map_flatten.fixed
index 51732e02be4..7ac368878ab 100644
--- a/tests/ui/map_flatten.fixed
+++ b/tests/ui/map_flatten.fixed
@@ -5,4 +5,5 @@
fn main() {
let _: Vec<_> = vec![5_i8; 6].into_iter().flat_map(|x| 0..x).collect();
+ let _: Option<_> = (Some(Some(1))).and_then(|x| x);
}
diff --git a/tests/ui/map_flatten.rs b/tests/ui/map_flatten.rs
index 66137a50ae8..a608601039c 100644
--- a/tests/ui/map_flatten.rs
+++ b/tests/ui/map_flatten.rs
@@ -5,4 +5,5 @@
fn main() {
let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
+ let _: Option<_> = (Some(Some(1))).map(|x| x).flatten();
}
diff --git a/tests/ui/map_flatten.stderr b/tests/ui/map_flatten.stderr
index e2ebd89b4c4..3cf2abd5b6d 100644
--- a/tests/ui/map_flatten.stderr
+++ b/tests/ui/map_flatten.stderr
@@ -6,5 +6,11 @@ LL | let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().colle
|
= note: `-D clippy::map-flatten` implied by `-D warnings`
-error: aborting due to previous error
+error: called `map(..).flatten()` on an `Option`. This is more succinctly expressed by calling `.and_then(..)`
+ --> $DIR/map_flatten.rs:8:24
+ |
+LL | let _: Option<_> = (Some(Some(1))).map(|x| x).flatten();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `and_then` instead: `(Some(Some(1))).and_then(|x| x)`
+
+error: aborting due to 2 previous errors