allow collect returns

lints/par_iter/src/lib.rs

@@ -19,7 +19,7 @@ use clippy_utils::{get_parent_expr, get_trait_def_id};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::Visitor;
-use rustc_hir::{self as hir};
+use rustc_hir::{self as hir, ExprKind};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_middle::ty::{self, ty_kind::TyKind, Ty};
 use utils::{check_implements_par_iter, generate_suggestion, is_type_valid};
@@ -113,7 +113,13 @@ impl<'tcx> LateLintPass<'tcx> for ParIter {
 
                 // TODO: this needs to change and find a better solutions for returns
                 if let TyKind::Adt(_, _) = ty.kind() {
-                    return;
+                    if let ExprKind::MethodCall(path_segment, _, _, _) = top_expr.kind {
+                        if path_segment.ident.as_str() != "collect" {
+                            return;
+                        }
+                    } else {
+                        return;
+                    }
                 }
 
                 let mut validator = Validator { cx, is_valid: true };

lints/par_iter/ui/main.fixed

@@ -232,3 +232,25 @@ fn simple_fold() {
     });
     println!("Sum: {}", sum);
 }
+
+// should parallelize
+fn collect_at_end() {
+    let people = vec![
+        Person {
+            name: "Alice".to_string(),
+            age: 25,
+        },
+        Person {
+            name: "Bob".to_string(),
+            age: 35,
+        },
+        Person {
+            name: "Carol".to_string(),
+            age: 32,
+        },
+    ];
+
+    let names: Vec<String> = people.par_iter().map(|p| p.name.clone()).collect();
+
+    println!("{:?}", names);
+}

lints/par_iter/ui/main.rs

@@ -232,3 +232,25 @@ fn simple_fold() {
     });
     println!("Sum: {}", sum);
 }
+
+// should parallelize
+fn collect_at_end() {
+    let people = vec![
+        Person {
+            name: "Alice".to_string(),
+            age: 25,
+        },
+        Person {
+            name: "Bob".to_string(),
+            age: 35,
+        },
+        Person {
+            name: "Carol".to_string(),
+            age: 32,
+        },
+    ];
+
+    let names: Vec<String> = people.iter().map(|p| p.name.clone()).collect();
+
+    println!("{:?}", names);
+}

lints/par_iter/ui/main.stderr

@@ -44,5 +44,11 @@ error: found iterator that can be parallelized
 LL |     numbers.iter().enumerate().for_each(|t| {
    |     ^^^^^^^^^^^^^^ help: try using a parallel iterator: `numbers.par_iter()`
 
-error: aborting due to 6 previous errors
+error: found iterator that can be parallelized
+  --> $DIR/main.rs:253:30
+   |
+LL |     let names: Vec<String> = people.iter().map(|p| p.name.clone()).collect();
+   |                              ^^^^^^^^^^^^^ help: try using a parallel iterator: `people.par_iter()`
+
+error: aborting due to 7 previous errors