fix #31238, ssavalue with no def with return on RHS (#35399)

Author: JeffBezanson

src/julia-syntax.scm

@@ -2348,7 +2348,7 @@
     'gc_preserve
     (lambda (e)
       (let* ((s (make-ssavalue))
-             (r (gensy)))
+             (r (make-ssavalue)))
         `(block
           (= ,s (gc_preserve_begin ,@(cddr e)))
           (= ,r ,(expand-forms (cadr e)))
@@ -4269,6 +4269,7 @@ f(x) = yt(x)
         (linetable    '(list))
         (labltable    (table))
         (ssavtable    (table))
+        (reachable    #t)
         (current-loc  0)
         (current-file file)
         (current-line line)
@@ -4279,13 +4280,16 @@ f(x) = yt(x)
                (not (and (pair? e) (eq? (car e) 'meta))))
           (begin (set! linetable (cons `(line ,line ,file) linetable))
                  (set! current-loc 1)))
-      (set! code (cons e code))
-      (set! i (+ i 1))
-      (set! locs (cons current-loc locs)))
+      (if (or reachable
+              (and (pair? e) (memq (car e) '(meta inbounds gc_preserve_begin gc_preserve_end aliasscope popaliasscope))))
+          (begin (set! code (cons e code))
+                 (set! i (+ i 1))
+                 (set! locs (cons current-loc locs)))))
     (let loop ((stmts (cdr body)))
       (if (pair? stmts)
           (let ((e (car stmts)))
-            (cond ((and (pair? e) (eq? (car e) 'line))
+            (cond ((atom? e) (emit e))
+                  ((eq? (car e) 'line)
                    (if (and (= current-line 0) (length= e 2) (pair? linetable))
                        ;; (line n) after push_loc just updates the line for the new file
                        (begin (set-car! (cdr (car linetable)) (cadr e))
@@ -4311,13 +4315,21 @@ f(x) = yt(x)
                      (set! current-loc (car l))
                      (set! current-line (cadr l))
                      (set! current-file (caddr l))))
-                  ((and (pair? e) (eq? (car e) 'label))
+                  ((eq? (car e) 'label)
+                   (set! reachable #t)
                    (put! labltable (cadr e) i))
                   ((and (assignment? e) (ssavalue? (cadr e)))
-                   (put! ssavtable (cadr (cadr e)) i)
-                   (emit (caddr e)))
+                   (let ((idx (and (ssavalue? (caddr e)) (get ssavtable (cadr (caddr e)) #f))))
+                     ;; if both lhs and rhs are ssavalues, merge them
+                     (if idx
+                         (put! ssavtable (cadr (cadr e)) idx)
+                         (begin
+                           (put! ssavtable (cadr (cadr e)) i)
+                           (emit (caddr e))))))
                   (else
-                   (emit e)))
+                   (emit e)
+                   (if (or (eq? (car e) 'goto) (eq? (car e) 'return))
+                       (set! reachable #f))))
             (loop (cdr stmts)))))
     (vector (reverse code) (reverse locs) (reverse linetable) ssavtable labltable)))
 

test/syntax.jl

@@ -2219,6 +2219,15 @@ end
 @test Meta.parse("aa\UE0080", raise=false) ==
     Expr(:error, "invalid character \"\Ue0080\" near column 3")
 
+# issue #31238
+a31238, b31238 = let x
+    return 1
+end
+@test !@isdefined(a31238) && !@isdefined(b31238)
+@test @eval((a31238, b31238) = let x
+    return 1
+end) === 1
+
 # issue #35201
 h35201(x; k=1) = (x, k)
 f35201(c) = h35201((;c...), k=true)