Variable Depth Limited to 2.

Summary

While having variables use other variables, values get used only until a depth of 2. The third depth just uses the variable name.

Steps to reproduce

Here is a sample .gitlab-ci.yml file that shows the issue:

image: docker:git

variables:
  VAR_A: A
  VAR_B: B_$VAR_A
  VAR_C: C_$VAR_B
  VAR_D: D_$VAR_C
  
review:
  variables:
    LOCAL_A: A
    LOCAL_B: B_$LOCAL_A
    LOCAL_C: C_$LOCAL_B
    LOCAL_D: D_$LOCAL_C
    MIXED_A: M_$VAR_A
    MIXED_B: M_$VAR_B
    MIXED_C: M_$VAR_C
    MIXED_D: M_$VAR_D
  script:
    - echo $VAR_A
    - echo $VAR_B
    - echo $VAR_C
    - echo $VAR_D
    - echo $LOCAL_A
    - echo $LOCAL_B
    - echo $LOCAL_C
    - echo $LOCAL_D
    - echo $MIXED_A
    - echo $MIXED_B
    - echo $MIXED_C
    - echo $MIXED_D

What is the current bug behavior?

Job Output:

$ echo $VAR_A
A
$ echo $VAR_B
B_A
$ echo $VAR_C
C_B_$VAR_A
$ echo $VAR_D
D_C_$VAR_B
$ echo $LOCAL_A
A
$ echo $LOCAL_B
B_A
$ echo $LOCAL_C
C_B_$LOCAL_A
$ echo $LOCAL_D
D_C_$LOCAL_B
$ echo $MIXED_A
M_A
$ echo $MIXED_B
M_B_$VAR_A
$ echo $MIXED_C
M_C_$VAR_B
$ echo $MIXED_D
M_D_$VAR_C

Variables do not fully flatten their values. Variable values are not consistent, depending on usage depth (see VAR_B's usage).

What is the expected correct behavior?

Variables should fully expand. Variables' values should at least be consistent -- regardless of usage context.

Example Project

I've made this public project to demonstrate the issue: https://gitlab.com/CauhxMilloy/ci-variable-depth-bug

Here is the ci run: https://gitlab.com/CauhxMilloy/ci-variable-depth-bug/-/jobs/53313550

Other Comments

I'm new to Gitlab and Gitlab CIs. I don't know if this is just an error or oversight on my part. I looked through CI variable documentation and Issues related to variables. I'm not sure if I maybe overlooked some config parameter that controls expansion depth (that is defaulted to 2)..? I couldn't find anything, so I'm filing this issue... sorry if I overlooked something.