fix: needless_for_each suggests wrongly when closure has no braces

Author: profetia

clippy_lints/src/needless_for_each.rs

@@ -99,11 +99,21 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessForEach {
                 )
             };
 
+            let body_param_sugg = snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability);
+            let for_each_rev_sugg = snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability);
+            let body_value_sugg = snippet_with_applicability(cx, body.value.span, "..", &mut applicability);
+
             let sugg = format!(
                 "for {} in {} {}",
-                snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability),
-                snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability),
-                snippet_with_applicability(cx, body.value.span, "..", &mut applicability),
+                body_param_sugg,
+                for_each_rev_sugg,
+                if let ExprKind::Block(block, _) = body.value.kind
+                    && is_let_desugar(block)
+                {
+                    format!("{{ {body_value_sugg} }}")
+                } else {
+                    body_value_sugg.to_string()
+                }
             );
 
             span_lint_and_then(cx, NEEDLESS_FOR_EACH, stmt.span, "needless use of `for_each`", |diag| {
@@ -116,6 +126,20 @@ impl<'tcx> LateLintPass<'tcx> for NeedlessForEach {
     }
 }
 
+/// Check if the block is a desugared `_ = expr` statement.
+fn is_let_desugar(block: &Block<'_>) -> bool {
+    matches!(
+        block,
+        Block {
+            stmts: [Stmt {
+                kind: StmtKind::Let(_),
+                ..
+            },],
+            ..
+        }
+    )
+}
+
 /// This type plays two roles.
 /// 1. Collect spans of `return` in the closure body.
 /// 2. Detect use of `return` in `Loop` in the closure body.

tests/ui/needless_for_each_fixable.fixed

@@ -128,3 +128,9 @@ fn should_not_lint() {
 }
 
 fn main() {}
+
+fn issue14734(rows: &[u8]) {
+    let mut v = vec![];
+    for x in rows.iter() { _ = v.push(x) }
+    //~^ needless_for_each
+}

tests/ui/needless_for_each_fixable.rs

@@ -128,3 +128,9 @@ fn should_not_lint() {
 }
 
 fn main() {}
+
+fn issue14734(rows: &[u8]) {
+    let mut v = vec![];
+    rows.iter().for_each(|x| _ = v.push(x));
+    //~^ needless_for_each
+}

tests/ui/needless_for_each_fixable.stderr

@@ -136,5 +136,11 @@ LL +         acc += elem;
 LL +     }
    |
 
-error: aborting due to 8 previous errors
+error: needless use of `for_each`
+  --> tests/ui/needless_for_each_fixable.rs:134:5
+   |
+LL |     rows.iter().for_each(|x| _ = v.push(x));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `for x in rows.iter() { _ = v.push(x) }`
+
+error: aborting due to 9 previous errors