fix: if_then_some_else_none FP when require type coercion

Author: profetia

clippy_lints/src/if_then_some_else_none.rs

@@ -5,7 +5,8 @@ use clippy_utils::msrvs::{self, Msrv};
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::sugg::Sugg;
 use clippy_utils::{
-    contains_return, higher, is_else_clause, is_in_const_context, is_res_lang_ctor, path_res, peel_blocks,
+    contains_return, expr_requires_coercion, higher, is_else_clause, is_in_const_context, is_res_lang_ctor, path_res,
+    peel_blocks,
 };
 use rustc_errors::Applicability;
 use rustc_hir::LangItem::{OptionNone, OptionSome};
@@ -92,6 +93,10 @@ impl<'tcx> LateLintPass<'tcx> for IfThenSomeElseNone {
                 expr.span,
                 format!("this could be simplified with `bool::{method_name}`"),
                 |diag| {
+                    if expr_requires_coercion(cx, then_expr) {
+                        return;
+                    }
+
                     let mut app = Applicability::MachineApplicable;
                     let cond_snip = Sugg::hir_with_context(cx, cond, expr.span.ctxt(), "[condition]", &mut app)
                         .maybe_paren()

tests/ui/if_then_some_else_none_unfixable.rs

@@ -0,0 +1,20 @@
+//@no-rustfix
+
+#![warn(clippy::if_then_some_else_none)]
+#![allow(clippy::manual_is_multiple_of)]
+
+mod issue15257 {
+    #[derive(Default)]
+    pub struct Foo {}
+    pub trait Bar {}
+    impl Bar for Foo {}
+
+    fn maybe_get_bar(i: u32) -> Option<Box<dyn Bar>> {
+        if i % 2 == 0 {
+            //~^ if_then_some_else_none
+            Some(Box::new(Foo::default()))
+        } else {
+            None
+        }
+    }
+}

tests/ui/if_then_some_else_none_unfixable.stderr

@@ -0,0 +1,16 @@
+error: this could be simplified with `bool::then`
+  --> tests/ui/if_then_some_else_none_unfixable.rs:13:9
+   |
+LL | /         if i % 2 == 0 {
+LL | |
+LL | |             Some(Box::new(Foo::default()))
+LL | |         } else {
+LL | |             None
+LL | |         }
+   | |_________^
+   |
+   = note: `-D clippy::if-then-some-else-none` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::if_then_some_else_none)]`
+
+error: aborting due to 1 previous error
+