Use a proper test for if the parameter is unused

Instead of comparing it to a wildcard, we actually check that it is
unused using a utility from `clippy_utils`.

Author: rspencer01

clippy_lints/src/methods/map_with_unused_argument_over_ranges.rs

@@ -1,8 +1,8 @@
 use crate::methods::MAP_WITH_UNUSED_ARGUMENT_OVER_RANGES;
 use clippy_config::msrvs::{self, Msrv};
 use clippy_utils::diagnostics::span_lint_and_then;
-use clippy_utils::higher;
 use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::usage;
 use rustc_ast::ast::RangeLimits;
 use rustc_ast::LitKind;
 use rustc_data_structures::packed::Pu128;
@@ -64,9 +64,9 @@ pub(super) fn check(
     let mut applicability = Applicability::MaybeIncorrect;
     if let Some(range) = higher::Range::hir(receiver)
         && let ExprKind::Closure(Closure { body, .. }) = arg.kind
-        && let Body { params: [param], .. } = cx.tcx.hir().body(*body)
-        // TODO: We should also look for a named, but unused parameter here
-        && matches!(param.pat.kind, PatKind::Wild)
+        && let body_hir = cx.tcx.hir().body(*body)
+        && let Body { params: [param], .. } = body_hir
+        && !usage::BindingUsageFinder::are_params_used(cx, body_hir)
         && let Some(count) = extract_count_with_applicability(cx, range, &mut applicability)
     {
         // TODO: Check if we can switch_to_eager_eval here and do away with `repeat_with` and instad use

tests/ui/map_with_unused_argument_over_ranges.fixed

@@ -18,6 +18,7 @@ macro_rules! gen {
 fn main() {
     // These should be raised
     std::iter::repeat_with(|| do_something()).take(10);
+    std::iter::repeat_with(|| do_something()).take(10);
     std::iter::repeat_with(|| do_something()).take(11);
     std::iter::repeat_with(|| do_something()).take(7);
     std::iter::repeat_with(|| do_something()).take(8);
@@ -42,8 +43,6 @@ fn main() {
     (lower..upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (lower_fn()..upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (lower_fn()..=upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
-    (0..10).map(|x| do_something()); // We do not detect unused parameters
-    (0..10).map(|x| do_something()).collect::<Vec<_>>(); // We do not detect unused parameters
     (0..10).map(|x| do_something_interesting(x, 4)); // Actual map over range
     "Foobar".chars().map(|_| do_something()); // Not a map over range
 }

tests/ui/map_with_unused_argument_over_ranges.rs

@@ -18,6 +18,7 @@ macro_rules! gen {
 fn main() {
     // These should be raised
     (0..10).map(|_| do_something());
+    (0..10).map(|_foo| do_something());
     (0..=10).map(|_| do_something());
     (3..10).map(|_| do_something());
     (3..=10).map(|_| do_something());
@@ -42,8 +43,6 @@ fn main() {
     (lower..upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (lower_fn()..upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
     (lower_fn()..=upper_fn()).map(|_| do_something()); // Ranges not starting at zero not yet handled
-    (0..10).map(|x| do_something()); // We do not detect unused parameters
-    (0..10).map(|x| do_something()).collect::<Vec<_>>(); // We do not detect unused parameters
     (0..10).map(|x| do_something_interesting(x, 4)); // Actual map over range
     "Foobar".chars().map(|_| do_something()); // Not a map over range
 }

tests/ui/map_with_unused_argument_over_ranges.stderr

@@ -15,6 +15,18 @@ LL +     std::iter::repeat_with(|| do_something()).take(10);
 error: map of a closure that does not depend on its parameter over a range
   --> tests/ui/map_with_unused_argument_over_ranges.rs:21:5
    |
+LL |     (0..10).map(|_foo| do_something());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: remove the explicit range and use `repeat_with` and `take`
+   |
+LL -     (0..10).map(|_foo| do_something());
+LL +     std::iter::repeat_with(|| do_something()).take(10);
+   |
+
+error: map of a closure that does not depend on its parameter over a range
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:22:5
+   |
 LL |     (0..=10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
@@ -25,7 +37,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(11);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:22:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:23:5
    |
 LL |     (3..10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -37,7 +49,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(7);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:23:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:24:5
    |
 LL |     (3..=10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -49,7 +61,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(8);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:24:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:25:5
    |
 LL |     (0..10).map(|_| 3);
    |     ^^^^^^^^^^^^^^^^^^
@@ -61,7 +73,7 @@ LL +     std::iter::repeat_with(|| 3).take(10);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:25:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:26:5
    |
 LL | /     (0..10).map(|_| {
 LL | |         let x = 3;
@@ -78,7 +90,7 @@ LL ~     }).take(10);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:29:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:30:5
    |
 LL |     (0..10).map(|_| do_something()).collect::<Vec<_>>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -90,7 +102,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(10).collect::<Vec<_>>();
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:31:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:32:5
    |
 LL |     (0..upper).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -102,7 +114,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:33:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:34:5
    |
 LL |     (0..upper_fn()).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -114,7 +126,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper_fn());
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:34:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:35:5
    |
 LL |     (0..=upper_fn()).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -126,7 +138,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper_fn() + 1);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:35:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:36:5
    |
 LL |     (2..upper_fn()).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -138,7 +150,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper_fn() - 2);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:36:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:37:5
    |
 LL |     (2..=upper_fn()).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -150,7 +162,7 @@ LL +     std::iter::repeat_with(|| do_something()).take(upper_fn() - 1);
    |
 
 error: map of a closure that does not depend on its parameter over a range
-  --> tests/ui/map_with_unused_argument_over_ranges.rs:58:5
+  --> tests/ui/map_with_unused_argument_over_ranges.rs:57:5
    |
 LL |     (0..10).map(|_| do_something());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -161,5 +173,5 @@ LL -     (0..10).map(|_| do_something());
 LL +     std::iter::repeat_with(|| do_something()).take(10);
    |
 
-error: aborting due to 13 previous errors
+error: aborting due to 14 previous errors