From bc4e207dcd0dbc957b4a398488ec7495c47b42e8 Mon Sep 17 00:00:00 2001
From: Jeff Bezanson <jeff.bezanson@gmail.com>
Date: Tue, 9 Feb 2021 15:08:55 -0500
Subject: [PATCH] fix bug in `let` when a global var is both shadowed and used
 in an RHS (#39570)

---
 src/julia-syntax.scm | 44 ++++++++++++++------------------------------
 test/core.jl         |  9 ---------
 test/syntax.jl       | 18 ++++++++++++++++++
 3 files changed, 32 insertions(+), 39 deletions(-)

diff --git a/src/julia-syntax.scm b/src/julia-syntax.scm
index 6329293e3a795..bac71d5bc1dee 100644
--- a/src/julia-syntax.scm
+++ b/src/julia-syntax.scm
@@ -1221,41 +1221,25 @@
                     (decl?   (cadar binds)))
                 (let ((vname (decl-var (cadar binds))))
                   (loop (cdr binds)
-                        (if (expr-contains-eq vname (caddar binds))
-                            (let ((tmp (make-ssavalue)))
-                              `(scope-block
-                                (block ,@hs
-                                       (= ,tmp ,(caddar binds))
-                                       (scope-block
-                                        (block
-                                         (local-def ,(cadar binds))
-                                         (= ,vname ,tmp)
-                                         ,blk)))))
-                            `(scope-block
-                              (block ,@hs
-                               (local-def ,(cadar binds))
-                               (= ,vname ,(caddar binds))
-                               ,blk))))))
+                        (let ((tmp (make-ssavalue)))
+                          `(block (= ,tmp ,(caddar binds))
+                                  (scope-block
+                                   (block ,@hs
+                                          (local-def ,(cadar binds))
+                                          (= ,vname ,tmp)
+                                          ,blk)))))))
                ;; (a, b, c, ...) = rhs
                ((and (pair? (cadar binds))
                      (eq? (caadar binds) 'tuple))
                 (let ((vars (lhs-vars (cadar binds))))
                   (loop (cdr binds)
-                        (if (expr-contains-p (lambda (x) (memq x vars)) (caddr (car binds)))
-                            ;; use more careful lowering if there are name conflicts. issue #25652
-                            (let ((temp (make-ssavalue)))
-                              `(block
-                                (= ,temp ,(caddr (car binds)))
-                                (scope-block
-                                 (block ,@hs
-                                  ,@(map (lambda (v) `(local-def ,v)) vars)
-                                  (= ,(cadr (car binds)) ,temp)
-                                  ,blk))))
-                            `(scope-block
-                              (block ,@hs
-                               ,@(map (lambda (v) `(local-def ,v)) vars)
-                               ,(car binds)
-                               ,blk))))))
+                        (let ((tmp (make-ssavalue)))
+                          `(block (= ,tmp ,(caddar binds))
+                                  (scope-block
+                                   (block ,@hs
+                                          ,@(map (lambda (v) `(local-def ,v)) vars)
+                                          (= ,(cadar binds) ,tmp)
+                                          ,blk)))))))
                (else (error "invalid let syntax"))))
              (else (error "invalid let syntax")))))))))
 
diff --git a/test/core.jl b/test/core.jl
index 40d7e5748239b..f1f11d40af4c7 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -4124,15 +4124,6 @@ let ex = quote
     @test ex.args[2] == :test
 end
 
-# issue #25652
-x25652 = 1
-x25652_2 = let (x25652, _) = (x25652, nothing)
-    x25652 = x25652 + 1
-    x25652
-end
-@test x25652_2 == 2
-@test x25652 == 1
-
 # issue #15180
 function f15180(x::T) where T
     X = Vector{T}(undef, 1)
diff --git a/test/syntax.jl b/test/syntax.jl
index ac4ccef86660b..2df99168b6ee8 100644
--- a/test/syntax.jl
+++ b/test/syntax.jl
@@ -2678,3 +2678,21 @@ end
     @test f((b=3, c=2, a=4)) == (4, 3)
     @test_throws ErrorException f((;))
 end
+
+# issue #25652
+x25652 = 1
+x25652_2 = let (x25652, _) = (x25652, nothing)
+    x25652 = x25652 + 1
+    x25652
+end
+@test x25652_2 == 2
+@test x25652 == 1
+
+@test let x = x25652
+    x25652 = x+3
+    x25652
+end == 4
+@test let (x,) = (x25652,)
+    x25652 = x+3
+    x25652
+end == 4