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_adjustment_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_adjustment_requires_coercion(cx, then_arg) {
+                        return;
+                    }
+
                     let mut app = Applicability::MachineApplicable;
                     let cond_snip = Sugg::hir_with_context(cx, cond, expr.span.ctxt(), "[condition]", &mut app)
                         .maybe_paren()

clippy_utils/src/lib.rs

@@ -3567,3 +3567,14 @@ pub fn potential_return_of_enclosing_body(cx: &LateContext<'_>, expr: &Expr<'_>)
     // enclosing body.
     false
 }
+
+/// Checks if the expression has adjustments that require coercion, for example: dereferencing with
+/// overloaded deref, coercing pointers and `dyn` objects.
+pub fn expr_adjustment_requires_coercion(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
+    cx.typeck_results().expr_adjustments(expr).iter().any(|adj| {
+        !matches!(
+            adj.kind,
+            Adjust::Deref(None) | Adjust::Borrow(AutoBorrow::Ref(..)) | Adjust::ReborrowPin(..)
+        )
+    })
+}

tests/ui/if_then_some_else_none.fixed

@@ -122,3 +122,14 @@ const fn issue12103(x: u32) -> Option<u32> {
     // Should not issue an error in `const` context
     if x > 42 { Some(150) } else { None }
 }
+
+mod issue15257 {
+    struct Range {
+        start: u8,
+        end: u8,
+    }
+
+    fn can_be_safely_rewrite(rs: &[&Range]) -> Option<Vec<u8>> {
+        (rs.len() == 1 && rs[0].start == rs[0].end).then(|| vec![rs[0].start])
+    }
+}

tests/ui/if_then_some_else_none.rs

@@ -143,3 +143,19 @@ const fn issue12103(x: u32) -> Option<u32> {
     // Should not issue an error in `const` context
     if x > 42 { Some(150) } else { None }
 }
+
+mod issue15257 {
+    struct Range {
+        start: u8,
+        end: u8,
+    }
+
+    fn can_be_safely_rewrite(rs: &[&Range]) -> Option<Vec<u8>> {
+        if rs.len() == 1 && rs[0].start == rs[0].end {
+            //~^ if_then_some_else_none
+            Some(vec![rs[0].start])
+        } else {
+            None
+        }
+    }
+}

tests/ui/if_then_some_else_none.stderr

@@ -58,5 +58,16 @@ error: this could be simplified with `bool::then`
 LL |     if s == "1" { Some(true) } else { None }
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(s == "1").then(|| true)`
 
-error: aborting due to 6 previous errors
+error: this could be simplified with `bool::then`
+  --> tests/ui/if_then_some_else_none.rs:154:9
+   |
+LL | /         if rs.len() == 1 && rs[0].start == rs[0].end {
+LL | |
+LL | |             Some(vec![rs[0].start])
+LL | |         } else {
+LL | |             None
+LL | |         }
+   | |_________^ help: try: `(rs.len() == 1 && rs[0].start == rs[0].end).then(|| vec![rs[0].start])`
+
+error: aborting due to 7 previous errors
 

tests/ui/if_then_some_else_none_unfixable.rs

@@ -0,0 +1,18 @@
+#![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:11:9
+   |
+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
+