Fix suggestions that need parens

Author: ThibsG

clippy_lints/src/methods/mod.rs

@@ -4094,14 +4094,19 @@ fn lint_from_iter(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<
         if implements_trait(cx, ty, from_iter_id, &[]) && implements_trait(cx, arg_ty, iter_id, &[]);
         then {
             // `expr` implements `FromIterator` trait
-            let iter_expr = snippet(cx, args[0].span, "..");
+            let iter_expr = sugg::Sugg::hir(cx, &args[0], "..").maybe_par();
+            let sugg = if higher::range(&args[0]).is_some() {
+                format!("{}.collect::<{}>()", iter_expr, ty)
+            } else {
+                format!("{}.collect()", iter_expr)
+            };
             span_lint_and_sugg(
                 cx,
                 FROM_ITER_INSTEAD_OF_COLLECT,
                 expr.span,
                 "usage of `FromIterator::from_iter`",
                 "use `.collect()` instead of `::from_iter()`",
-                format!("{}.collect()", iter_expr),
+                sugg,
                 Applicability::MaybeIncorrect,
             );
         }

tests/ui/from_iter_instead_of_collect.rs

@@ -1,6 +1,6 @@
 #![warn(clippy::from_iter_instead_of_collect)]
 
-use std::collections::HashMap;
+use std::collections::{HashMap, VecDeque};
 use std::iter::FromIterator;
 
 fn main() {
@@ -10,4 +10,10 @@ fn main() {
     HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
 
     Vec::from_iter(vec![42u32]);
+
+    let a = vec![0, 1, 2];
+    assert_eq!(a, Vec::from_iter(0..3));
+
+    let mut b = VecDeque::from_iter(0..3);
+    b.push_back(4);
 }

tests/ui/from_iter_instead_of_collect.stderr

@@ -12,5 +12,17 @@ error: usage of `FromIterator::from_iter`
 LL |     HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `.collect()` instead of `::from_iter()`: `vec![5, 5, 5, 5].iter().enumerate().collect()`
 
-error: aborting due to 2 previous errors
+error: usage of `FromIterator::from_iter`
+  --> $DIR/from_iter_instead_of_collect.rs:15:19
+   |
+LL |     assert_eq!(a, Vec::from_iter(0..3));
+   |                   ^^^^^^^^^^^^^^^^^^^^ help: use `.collect()` instead of `::from_iter()`: `(0..3).collect::<std::vec::Vec<i32>>()`
+
+error: usage of `FromIterator::from_iter`
+  --> $DIR/from_iter_instead_of_collect.rs:17:17
+   |
+LL |     let mut b = VecDeque::from_iter(0..3);
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `.collect()` instead of `::from_iter()`: `(0..3).collect::<std::collections::VecDeque<i32>>()`
+
+error: aborting due to 4 previous errors