From deac82ad915db6c1fd6e9246fd4bb3310b7cd71f Mon Sep 17 00:00:00 2001
From: Cody Tapscott <84105208+topolarity@users.noreply.github.com>
Date: Mon, 18 Nov 2024 15:40:02 -0500
Subject: [PATCH] lowering: don't reverse handler order in `(pop-handler-list
 ...)` (#55871)

We were accidentally emitting a different pop order for `Expr(:leave,
...)` if you uncomment the `nothing` below:
```julia
let src = Meta.@lower let
    try
        try
            return 1
        catch
        end
    finally
        # nothing # <- uncomment me
    end
end
    println.(filter(stmt->Base.isexpr(stmt, :leave), src.args[1].code))
    nothing
end
```
---
 src/julia-syntax.scm | 19 ++++++++++---------
 test/syntax.jl       | 23 +++++++++++++++++++++++
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/src/julia-syntax.scm b/src/julia-syntax.scm
index e82c436e5a730..6a9558bb06ba5 100644
--- a/src/julia-syntax.scm
+++ b/src/julia-syntax.scm
@@ -4447,15 +4447,16 @@ f(x) = yt(x)
     (define (pop-handler-list src-tokens dest-tokens lab)
       (if (eq? src-tokens dest-tokens)
           #f
-          (let loop ((s src-tokens)
-                     (l '()))
-            (if (not (pair? s))
-                (if (null? lab)
-                  (error "Attempt to jump into catch block")
-                  (error (string "cannot goto label \"" lab "\" inside try/catch block"))))
-            (if (eq? (cdr s) dest-tokens)
-                (cons (car s) l)
-                (loop (cdr s) (cons (car s) l))))))
+          (reverse
+            (let loop ((s src-tokens)
+                       (l '()))
+              (if (not (pair? s))
+                  (if (null? lab)
+                    (error "Attempt to jump into catch block")
+                    (error (string "cannot goto label \"" lab "\" inside try/catch block"))))
+              (if (eq? (cdr s) dest-tokens)
+                  (cons (car s) l)
+                  (loop (cdr s) (cons (car s) l)))))))
     (define (emit-return tail x)
       (define (emit- x)
         (let* ((tmp (if ((if (null? catch-token-stack) valid-ir-return? simple-atom?) x)
diff --git a/test/syntax.jl b/test/syntax.jl
index c19721b5c54b3..1f9d1d592931b 100644
--- a/test/syntax.jl
+++ b/test/syntax.jl
@@ -3865,6 +3865,29 @@ end
     end
 end
 
+let src = Meta.@lower let
+    try
+        try
+            return 1
+        catch
+        end
+    finally
+        nothing
+    end
+end
+    code = src.args[1].code
+    for stmt in code
+        if Meta.isexpr(stmt, :leave) && length(stmt.args) > 1
+            # Expr(:leave, ...) should list the arguments to pop from
+            # inner-most scope to outer-most
+            @test issorted(Int[
+                (arg::Core.SSAValue).id
+                for arg in stmt.args
+            ]; rev=true)
+        end
+    end
+end
+
 # Test that globals can be `using`'d even if they are not yet defined
 module UndefGlobal54954
     global theglobal54954::Int