Add a test regarding structs with a new Option field

[randombit]

This checks that adding an Option field to a struct has the expected behavior, where

• For an old writer and new reader, the struct deserializes with a field of None
• For a new writer and an old reader, the struct deserializes with the value of the Option ignored.

Overview
This PR just adds a test. Within the crypto team we were not sure if this situation (adding an Option to a Candid struct) worked as we expected (CRP-2642). This test is to confirm our understanding. But it also seems like a nice test to have for the future.

[ggreif]

Looks totally reasonable to me! I just wonder why there was no test for this, as it is one of the cornerstones of Candid... 🧐

[github-actions]

Name	Max Mem (Kb)	Encode	Decode
blob	4_224	20_459_319 ($\textcolor{green}{-0.00\%}$)	12_083_680
btreemap	75_456	4_022_699_205 ($\textcolor{green}{-0.00\%}$)	15_670_422_014
nns	128	2_257_486 ($\textcolor{green}{-0.70\%}$)	5_490_152 ($\textcolor{green}{-0.24\%}$)
nns_list_proposal	1_088	7_038_159 ($\textcolor{green}{-0.44\%}$)	81_898_508 ($\textcolor{red}{0.01\%}$)
option_list	128	7_140_179 ($\textcolor{green}{-0.00\%}$)	25_749_409
text	6_336	20_455_442	17_839_559
variant_list	128	7_142_188	24_354_404
vec_int16	16_704	168_582_443 ($\textcolor{green}{-0.00\%}$)	1_073_765_826

• Parser cost: 18_786_807 ($\textcolor{green}{-0.00\%}$)
• Extra args: 3_240_083

Click to see raw report

---------------------------------------------------

Benchmark: blob
  total:
    instructions: 32.55 M (-0.00%) (change within noise threshold)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 20.46 M (-0.00%) (change within noise threshold)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 12.08 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: text
  total:
    instructions: 38.30 M (no change)
    heap_increase: 99 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 20.46 M (no change)
    heap_increase: 66 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 17.84 M (no change)
    heap_increase: 33 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: vec_int16
  total:
    instructions: 1.24 B (-0.00%) (change within noise threshold)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 168.58 M (-0.00%) (change within noise threshold)
    heap_increase: 261 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 1.07 B (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: btreemap
  total:
    instructions: 19.69 B (-0.00%) (change within noise threshold)
    heap_increase: 1179 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 4.02 B (-0.00%) (change within noise threshold)
    heap_increase: 159 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 15.67 B (no change)
    heap_increase: 1020 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: option_list
  total:
    instructions: 32.89 M (-0.00%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.14 M (-0.00%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 25.75 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: variant_list
  total:
    instructions: 31.50 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.14 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 24.35 M (no change)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns
  total:
    instructions: 27.37 M (-0.10%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  0. Parsing (scope):
    instructions: 18.79 M (-0.00%) (change within noise threshold)
    heap_increase: 2 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 2.26 M (-0.70%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 5.49 M (-0.24%) (change within noise threshold)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: nns_list_proposal
  total:
    instructions: 88.94 M (-0.03%) (change within noise threshold)
    heap_increase: 17 pages (no change)
    stable_memory_increase: 0 pages (no change)

  1. Encoding (scope):
    instructions: 7.04 M (-0.44%) (change within noise threshold)
    heap_increase: 3 pages (no change)
    stable_memory_increase: 0 pages (no change)

  2. Decoding (scope):
    instructions: 81.90 M (0.01%) (change within noise threshold)
    heap_increase: 14 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------

Benchmark: extra_args
  total:
    instructions: 3.24 M (no change)
    heap_increase: 0 pages (no change)
    stable_memory_increase: 0 pages (no change)

---------------------------------------------------
Successfully persisted results to canbench_results.yml

[randombit]

CI failure looks unrelated

[randombit]

There may well be some other test that covers this, I did look but I could not immediately find it