Improvements from PR feedback

clippy_lints/src/methods/mod.rs

@@ -1370,10 +1370,11 @@ declare_clippy_lint! {
 }
 
 declare_clippy_lint! {
-    /// **What it does:** Checks for `from_iter()` function calls that implements `FromIterator`
+    /// **What it does:** Checks for `from_iter()` function calls on types that implement the `FromIterator`
     /// trait.
     ///
-    /// **Why is this bad?** Makes code less readable especially in method chaining.
+    /// **Why is this bad?** It is recommended style to use collect. See
+    /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
     ///
     /// **Known problems:** None.
     ///
@@ -3873,18 +3874,19 @@ fn lint_filetype_is_file(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir
 
 fn lint_from_iter(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
     let ty = cx.typeck_results().expr_ty(expr);
-    let id = get_trait_def_id(cx, &paths::FROM_ITERATOR_TRAIT).unwrap();
+    let id = get_trait_def_id(cx, &paths::FROM_ITERATOR).unwrap();
 
     if implements_trait(cx, ty, id, &[]) {
         // `expr` implements `FromIterator` trait
         let iter_expr = snippet(cx, args[0].span, "..");
-        span_lint_and_help(
+        span_lint_and_sugg(
             cx,
             FROM_ITER_INSTEAD_OF_COLLECT,
             expr.span,
             "use `.collect()` instead of `::from_iter()`",
-            None,
-            &format!("consider using `{}.collect()`", iter_expr),
+            "consider using",
+            format!("`{}.collect()`", iter_expr),
+            Applicability::MaybeIncorrect
         );
     }
 }

clippy_lints/src/utils/paths.rs

@@ -44,7 +44,7 @@ pub const FN: [&str; 3] = ["core", "ops", "Fn"];
 pub const FN_MUT: [&str; 3] = ["core", "ops", "FnMut"];
 pub const FN_ONCE: [&str; 3] = ["core", "ops", "FnOnce"];
 pub const FROM_FROM: [&str; 4] = ["core", "convert", "From", "from"];
-pub const FROM_ITERATOR_TRAIT: [&str; 3] = ["std", "iter", "FromIterator"];
+pub const FROM_ITERATOR: [&str; 3] = ["std", "iter", "FromIterator"];
 pub const FROM_TRAIT: [&str; 3] = ["core", "convert", "From"];
 pub const FUTURE_FROM_GENERATOR: [&str; 3] = ["core", "future", "from_generator"];
 pub const HASH: [&str; 3] = ["core", "hash", "Hash"];

tests/ui/from_iter_instead_of_collect.rs

@@ -4,12 +4,8 @@ use std::collections::HashMap;
 use std::iter::FromIterator;
 
 fn main() {
-    {
-        let iter_expr = std::iter::repeat(5).take(5);
+    let iter_expr = std::iter::repeat(5).take(5);
 
-        Vec::from_iter(iter_expr);
-        HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
-        //let v: Vec<i32> = iter_expr.collect();
-        let a: Vec<i32> = Vec::new();
-    }
+    Vec::from_iter(iter_expr);
+    HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
 }

tests/ui/from_iter_instead_of_collect.stderr

@@ -1,19 +1,16 @@
 error: use `.collect()` instead of `::from_iter()`
-  --> $DIR/from_iter_instead_of_collect.rs:10:9
+  --> $DIR/from_iter_instead_of_collect.rs:9:5
    |
-LL |         Vec::from_iter(iter_expr);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     Vec::from_iter(iter_expr);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: ``iter_expr.collect()``
    |
    = note: `-D clippy::from-iter-instead-of-collect` implied by `-D warnings`
-   = help: consider using `iter_expr.collect()`
 
 error: use `.collect()` instead of `::from_iter()`
-  --> $DIR/from_iter_instead_of_collect.rs:11:9
+  --> $DIR/from_iter_instead_of_collect.rs:10:5
    |
-LL |         HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = help: consider using `vec![5, 5, 5, 5].iter().enumerate().collect()`
+LL |     HashMap::<usize, &i8>::from_iter(vec![5, 5, 5, 5].iter().enumerate());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: ``vec![5, 5, 5, 5].iter().enumerate().collect()``
 
 error: aborting due to 2 previous errors