Fixes manual_flatten removes the useless if let

clippy_lints/src/loops/manual_flatten.rs

@@ -2,6 +2,7 @@ use super::MANUAL_FLATTEN;
 use super::utils::make_iterator_snippet;
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::msrvs::{self, Msrv};
+use clippy_utils::source::{indent_of, reindent_multiline, snippet_with_applicability};
 use clippy_utils::visitors::is_local_used;
 use clippy_utils::{higher, path_to_local_id, peel_blocks_with_stmt};
 use rustc_errors::Applicability;
@@ -28,7 +29,7 @@ pub(super) fn check<'tcx>(
         && let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind
         && path_to_local_id(let_expr, pat_hir_id)
         // Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
-        && let PatKind::TupleStruct(ref qpath, _, _) = let_pat.kind
+        && let PatKind::TupleStruct(ref qpath, let_pats, _) = let_pat.kind
         && let Res::Def(DefKind::Ctor(..), ctor_id) = cx.qpath_res(qpath, let_pat.hir_id)
         && let Some(variant_id) = cx.tcx.opt_parent(ctor_id)
         && let some_ctor = cx.tcx.lang_items().option_some_variant() == Some(variant_id)
@@ -54,20 +55,35 @@ pub(super) fn check<'tcx>(
             _ => "",
         };
 
-        let sugg = format!("{arg_snippet}{copied}.flatten()");
+        let help_msg = "try `.flatten()` and remove the `if let` statement in the for loop";
 
-        // If suggestion is not a one-liner, it won't be shown inline within the error message. In that
-        // case, it will be shown in the extra `help` message at the end, which is why the first
-        // `help_msg` needs to refer to the correct relative position of the suggestion.
-        let help_msg = if sugg.contains('\n') {
-            "remove the `if let` statement in the for loop and then..."
+        let pat_snippet = if let_pats.is_empty() {
+            "_".to_string()
         } else {
-            "...and remove the `if let` statement in the for loop"
+            snippet_with_applicability(
+                cx,
+                let_pats.first().unwrap().span.source_callsite(),
+                "_",
+                &mut applicability,
+            )
+            .to_string()
         };
+        let body_snippet =
+            snippet_with_applicability(cx, if_then.span.source_callsite(), "[body]", &mut applicability).to_string();
+        let suggestions = vec![
+            // flatten the iterator
+            (arg.span, format!("{arg_snippet}{copied}.flatten()")),
+            (pat.span, pat_snippet),
+            // remove the `if let` statement
+            (
+                body.span,
+                reindent_multiline(&body_snippet, true, indent_of(cx, body.span)),
+            ),
+        ];
 
         span_lint_and_then(cx, MANUAL_FLATTEN, span, msg, |diag| {
-            diag.span_suggestion(arg.span, "try", sugg, applicability);
             diag.span_help(inner_expr.span, help_msg);
+            diag.multipart_suggestion("try", suggestions, applicability);
         });
     }
 }

tests/ui/manual_flatten.stderr

@@ -1,18 +1,15 @@
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:7:5
    |
-LL |       for n in x {
-   |       ^        - help: try: `x.into_iter().flatten()`
-   |  _____|
-   | |
+LL | /     for n in x {
 LL | |
 LL | |
 LL | |         if let Some(y) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:10:9
    |
 LL | /         if let Some(y) = n {
@@ -21,14 +18,17 @@ LL | |         }
    | |_________^
    = note: `-D clippy::manual-flatten` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::manual_flatten)]`
+help: try
+   |
+LL ~     for y in x.into_iter().flatten() {
+LL +         println!("{}", y);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:17:5
    |
-LL |       for n in y.clone() {
-   |       ^        --------- help: try: `y.clone().into_iter().flatten()`
-   |  _____|
-   | |
+LL | /     for n in y.clone() {
 LL | |
 LL | |
 LL | |         if let Ok(n) = n {
@@ -37,145 +37,169 @@ LL | |         };
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:20:9
    |
 LL | /         if let Ok(n) = n {
 LL | |             println!("{}", n);
 LL | |         };
    | |_________^
+help: try
+   |
+LL ~     for n in y.clone().into_iter().flatten() {
+LL +         println!("{}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:26:5
    |
-LL |       for n in &y {
-   |       ^        -- help: try: `y.iter().flatten()`
-   |  _____|
-   | |
+LL | /     for n in &y {
 LL | |
 LL | |
 LL | |         if let Ok(n) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:29:9
    |
 LL | /         if let Ok(n) = n {
 LL | |             println!("{}", n);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for n in y.iter().flatten() {
+LL +         println!("{}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Ok` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:36:5
    |
-LL |       for n in z {
-   |       ^        - help: try: `z.iter().flatten()`
-   |  _____|
-   | |
+LL | /     for n in z {
 LL | |
 LL | |
 LL | |         if let Ok(n) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:39:9
    |
 LL | /         if let Ok(n) = n {
 LL | |             println!("{}", n);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for n in z.iter().flatten() {
+LL +         println!("{}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:47:5
    |
-LL |       for n in z {
-   |       ^        - help: try: `z.flatten()`
-   |  _____|
-   | |
+LL | /     for n in z {
 LL | |
 LL | |
 LL | |         if let Some(m) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:50:9
    |
 LL | /         if let Some(m) = n {
 LL | |             println!("{}", m);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for m in z.flatten() {
+LL +         println!("{}", m);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:82:5
    |
-LL |       for n in &vec_of_ref {
-   |       ^        ----------- help: try: `vec_of_ref.iter().copied().flatten()`
-   |  _____|
-   | |
+LL | /     for n in &vec_of_ref {
 LL | |
 LL | |
 LL | |         if let Some(n) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:85:9
    |
 LL | /         if let Some(n) = n {
 LL | |             println!("{:?}", n);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for n in vec_of_ref.iter().copied().flatten() {
+LL +         println!("{:?}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:91:5
    |
-LL |       for n in vec_of_ref {
-   |       ^        ---------- help: try: `vec_of_ref.iter().copied().flatten()`
-   |  _____|
-   | |
+LL | /     for n in vec_of_ref {
 LL | |
 LL | |
 LL | |         if let Some(n) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:94:9
    |
 LL | /         if let Some(n) = n {
 LL | |             println!("{:?}", n);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for n in vec_of_ref.iter().copied().flatten() {
+LL +         println!("{:?}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:100:5
    |
-LL |       for n in slice_of_ref {
-   |       ^        ------------ help: try: `slice_of_ref.iter().copied().flatten()`
-   |  _____|
-   | |
+LL | /     for n in slice_of_ref {
 LL | |
 LL | |
 LL | |         if let Some(n) = n {
 ...  |
 LL | |     }
    | |_____^
    |
-help: ...and remove the `if let` statement in the for loop
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:103:9
    |
 LL | /         if let Some(n) = n {
 LL | |             println!("{:?}", n);
 LL | |         }
    | |_________^
+help: try
+   |
+LL ~     for n in slice_of_ref.iter().copied().flatten() {
+LL +         println!("{:?}", n);
+LL +     }
+   |
 
 error: unnecessary `if let` since only the `Some` variant of the iterator element is used
   --> tests/ui/manual_flatten.rs:132:5
@@ -188,7 +212,7 @@ LL | |         Some(1),
 LL | |     }
    | |_____^
    |
-help: remove the `if let` statement in the for loop and then...
+help: try `.flatten()` and remove the `if let` statement in the for loop
   --> tests/ui/manual_flatten.rs:139:9
    |
 LL | /         if let Some(n) = n {
@@ -201,6 +225,8 @@ LL |     for n in vec![
 ...
 LL |         Some(3)
 LL ~     ].iter().flatten() {
+LL +         println!("{:?}", n);
+LL +     }
    |
 
 error: aborting due to 9 previous errors