Fix clippy lint for identical if/else contraining ? expressions

src/tools/clippy/clippy_utils/src/hir_utils.rs

@@ -10,6 +10,7 @@ use rustc_hir::{
     GenericArgs, Guard, HirId, HirIdMap, InlineAsmOperand, Let, Lifetime, LifetimeName, Pat, PatField, PatKind, Path,
     PathSegment, PrimTy, QPath, Stmt, StmtKind, Ty, TyKind, TypeBinding,
 };
+use rustc_hir::MatchSource::TryDesugar;
 use rustc_lexer::{tokenize, TokenKind};
 use rustc_lint::LateContext;
 use rustc_middle::ty::TypeckResults;
@@ -311,7 +312,7 @@ impl HirEqInterExpr<'_, '_, '_> {
                 lls == rls && self.eq_block(lb, rb) && both(ll, rl, |l, r| l.ident.name == r.ident.name)
             },
             (&ExprKind::Match(le, la, ref ls), &ExprKind::Match(re, ra, ref rs)) => {
-                ls == rs
+                (ls == rs || (matches!((ls, rs), (TryDesugar(_), TryDesugar(_)))))
                     && self.eq_expr(le, re)
                     && over(la, ra, |l, r| {
                         self.eq_pat(l.pat, r.pat)

src/tools/clippy/tests/ui/if_same_then_else2.rs

@@ -98,7 +98,7 @@ fn if_same_then_else2() -> Result<&'static str, ()> {
     };
 
     if true {
-        // FIXME: should emit "this `if` has identical blocks"
+        //~^ ERROR: this `if` has identical blocks
         Ok("foo")?;
     } else {
         Ok("foo")?;

src/tools/clippy/tests/ui/if_same_then_else2.stderr

@@ -82,6 +82,25 @@ LL | |         f32::NAN
 LL | |     };
    | |_____^
 
+error: this `if` has identical blocks
+  --> $DIR/if_same_then_else2.rs:100:13
+   |
+LL |       if true {
+   |  _____________^
+LL | |
+LL | |         Ok("foo")?;
+LL | |     } else {
+   | |_____^
+   |
+note: same as this
+  --> $DIR/if_same_then_else2.rs:103:12
+   |
+LL |       } else {
+   |  ____________^
+LL | |         Ok("foo")?;
+LL | |     }
+   | |_____^
+
 error: this `if` has identical blocks
   --> $DIR/if_same_then_else2.rs:124:20
    |
@@ -103,5 +122,5 @@ LL | |         return Ok(&foo[0..]);
 LL | |     }
    | |_____^
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors