fix lambda-optimize-vars! with complex assignment RHSs (#30564)

fixes #30563

(cherry picked from commit 84a83ab)

src/julia-syntax.scm

@@ -2998,7 +2998,9 @@ f(x) = yt(x)
                          (kill))
                        (cdr e)))
             (else
-             (mark-used e)
+             (if (eq? (car e) '=)
+                 (visit (caddr e))
+                 (mark-used e))
              (if (and (or (eq? (car e) '=)
                           (and (eq? (car e) 'method) (length> e 2)))
                       (has? unused (cadr e)))

test/compiler/compiler.jl

@@ -1822,6 +1822,15 @@ function g15276()
 end
 @test g15276() isa Vector{Int}
 
+function inbounds_30563()
+    local y
+    @inbounds for i in 1:10
+        y = (m->2i)(0)
+    end
+    return y
+end
+@test Base.return_types(inbounds_30563, ()) == Any[Int]
+
 # issue #27316 - inference shouldn't hang on these
 f27316(::Vector) = nothing
 f27316(::Any) = f27316(Any[][1]), f27316(Any[][1])