Fix obfuscated_if_else suggestion on left side of a binary expr

An `if … { … } else { … }` used as the left operand of a binary
expression requires parentheses to be parsed as an expression.

clippy_lints/src/methods/obfuscated_if_else.rs

@@ -1,6 +1,7 @@
 use super::OBFUSCATED_IF_ELSE;
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::eager_or_lazy::switch_to_eager_eval;
+use clippy_utils::get_parent_expr;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::sugg::Sugg;
 use rustc_errors::Applicability;
@@ -41,6 +42,17 @@ pub(super) fn check<'tcx>(
             snippet_with_applicability(cx, unwrap_arg.span, "..", &mut applicability)
         );
 
+        // To be parsed as an expression, the `if { … } else { … }` as the left operand of a binary operator
+        // requires parentheses.
+        let sugg = if let Some(parent_expr) = get_parent_expr(cx, expr)
+            && let ExprKind::Binary(_, left, _) = parent_expr.kind
+            && left.hir_id == expr.hir_id
+        {
+            format!("({sugg})")
+        } else {
+            sugg
+        };
+
         span_lint_and_sugg(
             cx,
             OBFUSCATED_IF_ELSE,

tests/ui/obfuscated_if_else.fixed

@@ -16,3 +16,20 @@ fn main() {
     if true { a += 1 } else { () };
     if true { () } else { a += 2 };
 }
+
+fn issue11141() {
+    // Parentheses are required around the left side of a binary expression
+    let _ = (if true { 40 } else { 17 }) | 2;
+    // Parentheses are required only for the leftmost expression
+    let _ = (if true { 30 } else { 17 }) | if true { 2 } else { 3 } | if true { 10 } else { 1 };
+
+    // Parentheses are not required around the right side of a binary expression
+    let _ = 2 | if true { 40 } else { 17 };
+
+    // Parentheses are not required for a cast
+    let _ = if true { 42 } else { 17 } as u8;
+    // Parentheses are not required for a deref
+    let _ = *if true { &42 } else { &17 };
+    // Parentheses are not required for a deref followed by a cast
+    let _ = *if true { &42 } else { &17 } as u8;
+}

tests/ui/obfuscated_if_else.rs

@@ -16,3 +16,20 @@ fn main() {
     true.then_some(a += 1).unwrap_or(());
     true.then_some(()).unwrap_or(a += 2);
 }
+
+fn issue11141() {
+    // Parentheses are required around the left side of a binary expression
+    let _ = true.then_some(40).unwrap_or(17) | 2;
+    // Parentheses are required only for the leftmost expression
+    let _ = true.then_some(30).unwrap_or(17) | true.then_some(2).unwrap_or(3) | true.then_some(10).unwrap_or(1);
+
+    // Parentheses are not required around the right side of a binary expression
+    let _ = 2 | true.then_some(40).unwrap_or(17);
+
+    // Parentheses are not required for a cast
+    let _ = true.then_some(42).unwrap_or(17) as u8;
+    // Parentheses are not required for a deref
+    let _ = *true.then_some(&42).unwrap_or(&17);
+    // Parentheses are not required for a deref followed by a cast
+    let _ = *true.then_some(&42).unwrap_or(&17) as u8;
+}

tests/ui/obfuscated_if_else.stderr

@@ -37,5 +37,53 @@ error: this method chain can be written more clearly with `if .. else ..`
 LL |     true.then_some(()).unwrap_or(a += 2);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { () } else { a += 2 }`
 
-error: aborting due to 6 previous errors
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:22:13
+   |
+LL |     let _ = true.then_some(40).unwrap_or(17) | 2;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(if true { 40 } else { 17 })`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:24:13
+   |
+LL |     let _ = true.then_some(30).unwrap_or(17) | true.then_some(2).unwrap_or(3) | true.then_some(10).unwrap_or(1);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `(if true { 30 } else { 17 })`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:24:48
+   |
+LL |     let _ = true.then_some(30).unwrap_or(17) | true.then_some(2).unwrap_or(3) | true.then_some(10).unwrap_or(1);
+   |                                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { 2 } else { 3 }`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:24:81
+   |
+LL |     let _ = true.then_some(30).unwrap_or(17) | true.then_some(2).unwrap_or(3) | true.then_some(10).unwrap_or(1);
+   |                                                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { 10 } else { 1 }`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:27:17
+   |
+LL |     let _ = 2 | true.then_some(40).unwrap_or(17);
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { 40 } else { 17 }`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:30:13
+   |
+LL |     let _ = true.then_some(42).unwrap_or(17) as u8;
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { 42 } else { 17 }`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:32:14
+   |
+LL |     let _ = *true.then_some(&42).unwrap_or(&17);
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { &42 } else { &17 }`
+
+error: this method chain can be written more clearly with `if .. else ..`
+  --> tests/ui/obfuscated_if_else.rs:34:14
+   |
+LL |     let _ = *true.then_some(&42).unwrap_or(&17) as u8;
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `if true { &42 } else { &17 }`
+
+error: aborting due to 14 previous errors