Don't emit machine applicable map_flatten lint if there are code comments (#13940)

Fixes rust-lang/rust-clippy#8528.

Similar to #13911, if there are code comments, we don't want to remove
them automatically.

changelog: Don't emit machine applicable `map_flatten` lint if there are
code comments

r? @xFrednet

Author: xFrednet

clippy_lints/src/methods/map_flatten.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::is_trait_method;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{is_trait_method, span_contains_comment};
 use rustc_errors::Applicability;
 use rustc_hir::Expr;
 use rustc_lint::LateContext;
@@ -17,10 +17,15 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, map_
         let mut applicability = Applicability::MachineApplicable;
 
         let closure_snippet = snippet_with_applicability(cx, map_arg.span, "..", &mut applicability);
+        let span = expr.span.with_lo(map_span.lo());
+        // If the methods are separated with comments, we don't apply suggestion automatically.
+        if span_contains_comment(cx.tcx.sess.source_map(), span) {
+            applicability = Applicability::Unspecified;
+        }
         span_lint_and_sugg(
             cx,
             MAP_FLATTEN,
-            expr.span.with_lo(map_span.lo()),
+            span,
             format!("called `map(..).flatten()` on `{caller_ty_name}`"),
             format!("try replacing `map` with `{method_to_use}` and remove the `.flatten()`"),
             format!("{method_to_use}({closure_snippet})"),

tests/ui/map_flatten.rs

@@ -55,6 +55,18 @@ fn long_span() {
         .collect();
 }
 
+#[allow(clippy::useless_vec)]
+fn no_suggestion_if_comments_present() {
+    let vec = vec![vec![1, 2, 3]];
+    let _ = vec
+        .iter()
+        // a lovely comment explaining the code in very detail
+        .map(|x| x.iter())
+        //~^ ERROR: called `map(..).flatten()` on `Iterator`
+        // the answer to life, the universe and everything could be here
+        .flatten();
+}
+
 fn main() {
     long_span();
 }

tests/ui/map_flatten.stderr

@@ -102,5 +102,14 @@ LL +             }
 LL +         })
    |
 
-error: aborting due to 4 previous errors
+error: called `map(..).flatten()` on `Iterator`
+  --> tests/ui/map_flatten.rs:64:10
+   |
+LL |           .map(|x| x.iter())
+   |  __________^
+...  |
+LL | |         .flatten();
+   | |__________________^ help: try replacing `map` with `flat_map` and remove the `.flatten()`: `flat_map(|x| x.iter())`
+
+error: aborting due to 5 previous errors