lowering: Don't mutate lambda in linearize (#57416)

Fixes #56904.

The associated PR (#55876) compiles a finally block, then compiles a
renumbered version of it. This works if `compile` doesn't mutate its
input, but in reality, lambda bodies were being `set!` when linearized.
The "invalid syntax" error was a result of attempting to linearize a
lambda twice.

Author: mlechu

src/julia-syntax.scm

@@ -4322,11 +4322,10 @@ f(x) = yt(x)
 (define (linearize e)
   (cond ((or (not (pair? e)) (quoted? e)) e)
         ((eq? (car e) 'lambda)
-         (set-car! (cdddr e) (compile-body (cadddr e) (append (car (caddr e))
-                                                              (cadr (caddr e)))
-                                           e)))
-        (else (for-each linearize (cdr e))))
-  e)
+         (list-set e 3 (compile-body (cadddr e)
+                                     (append (car (caddr e))
+                                             (cadr (caddr e))) e)))
+        (else (cons (car e) (map linearize (cdr e))))))
 
 (define (valid-ir-argument? e)
   (or (simple-atom? e)

src/utils.scm

@@ -119,3 +119,16 @@
          (cons (car lst) (filter (lambda (x) (not (pred x))) (cdr lst))))
         (else
          (cons (car lst) (keep-first pred (cdr lst))))))
+
+(define (take lst n)
+  (let loop ((lst lst) (n n) (out '()))
+    (if (= n 0) (reverse out)
+        (loop (cdr lst) (- n 1) (cons (car lst) out)))))
+
+(define (drop lst n)
+  (if (= n 0) lst
+      (drop (cdr lst) (- n 1))))
+
+;; functional update at position i
+(define (list-set lst i val)
+  (append (take lst i) (list val) (drop lst (+ i 1))))

test/syntax.jl

@@ -4102,3 +4102,7 @@ module Ambig57404
     using .B
 end
 @test Ambig57404.S == 1
+
+# Issue #56904 - lambda linearized twice
+@test (let; try 3; finally try 1; f(() -> x); catch x; end; end; x = 7; end) === 7
+@test (let; try 3; finally try 4; finally try 1; f(() -> x); catch x; end; end; end; x = 7; end) === 7