[NIT-3992] Add linter for imposible json omitempty

[pmikolajczyk41]

Problem

json:"...,omitempty"  doesn't work for golang arrays if they don't have zero length - if a field is an array type and not slice then it's always included in the marshaled json string. Same for structs, aliases etc.

Why it's bad: it's easy to break backward compatibility or even introduce diversion, e.g. if you add optional field to params.ChainConfig.ArbitrumChainParams of type common.Address that happens to be type Address [AddressLength]byte, the genesis block state will diverge - when initializing ArbOS, chain config is marshaled to json and saved to arbos state.

Solution

The only existing linter for this was: https://github.com/andydotdev/omitlint. However:

• it doesn't seem to be maintained anymore
• no stars, usages, mentions in Google browse
• not compatible with https://golangci-lint.run/docs/plugins/module-plugins/
• installing it as a separate binary adds to repo requirement + might not be that safe
• simple enough to adapt and reimplement quickly

So I simply added a new linter to our in-house set. Fortunately, it seems that our codebase is not affected by an incorrect usage of omitempty.

[github-actions]

❌ 3 Tests Failed:

Tests completed	Failed	Passed	Skipped
2141	3	2138	0

View the top 3 failed tests by shortest run time

TestVersion40

Stack Traces | 5.110s run time

... [CONTENT TRUNCATED: Keeping last 20 lines]
=== CONT  TestVersion40
    precompile_inclusion_test.go:90: goroutine 454872 [running]:
        runtime/debug.Stack()
        	/opt/hostedtoolcache/go/1.25.3/x64/src/runtime/debug/stack.go:26 +0x5e
        github.com/offchainlabs/nitro/util/testhelpers.RequireImpl({0x40824d0, 0xc076687340}, {0x4040700, 0xc152bfabd0}, {0x0, 0x0, 0x0})
        	/home/runner/work/nitro/nitro/util/testhelpers/testhelpers.go:29 +0x55
        github.com/offchainlabs/nitro/system_tests.Require(0xc076687340, {0x4040700, 0xc152bfabd0}, {0x0, 0x0, 0x0})
        	/home/runner/work/nitro/nitro/system_tests/common_test.go:1723 +0x5d
        github.com/offchainlabs/nitro/system_tests.testPrecompiles(0xc076687340, 0x28, {0xc083b65df8, 0x5, 0x39?})
        	/home/runner/work/nitro/nitro/system_tests/precompile_inclusion_test.go:90 +0x371
        github.com/offchainlabs/nitro/system_tests.TestVersion40(0xc076687340?)
        	/home/runner/work/nitro/nitro/system_tests/precompile_inclusion_test.go:71 +0x64b
        testing.tRunner(0xc076687340, 0x3ccaa48)
        	/opt/hostedtoolcache/go/1.25.3/x64/src/testing/testing.go:1934 +0xea
        created by testing.(*T).Run in goroutine 1
        	/opt/hostedtoolcache/go/1.25.3/x64/src/testing/testing.go:1997 +0x465
        
    precompile_inclusion_test.go:90: �[31;1m [] execution aborted (timeout = 5s) �[0;0m
�[90mposted new batch 50�[0;0m
--- FAIL: TestVersion40 (5.11s)

TestEthSyncing

Stack Traces | 22.430s run time

... [CONTENT TRUNCATED: Keeping last 20 lines]
DEBUG[10-16|09:58:14.051] Journaled pathdb diff layer              root=bd9dba..0235b5 parent=157621..d69964 id=67                 block=66
INFO [10-16|09:58:14.052] Persisted dirty state to disk            size=291.24KiB elapsed=5.730ms
INFO [10-16|09:58:14.052] Blockchain stopped
TRACE[10-16|09:58:14.052] P2P networking is spinning down
INFO [10-16|09:58:14.053] New Key                                  name=Faucet            Address=0xaF24Ca6c2831f4d4F629418b50C227DF0885613A
INFO [10-16|09:58:14.053] New Key                                  name=RollupOwner       Address=0x57Ff0F473737a1c161bfF9efDF016F7991585088
INFO [10-16|09:58:14.053] New Key                                  name=Sequencer         Address=0xb386a74Dcab67b66F8AC07B4f08365d37495Dd23
INFO [10-16|09:58:14.054] New Key                                  name=Validator         Address=0x83FFCFaCE2Fb0E1286686815503608A16EF41e47
INFO [10-16|09:58:14.054] New Key                                  name=User              Address=0x7E23C8862920797d81916d62c274dd9217113e28
INFO [10-16|09:58:14.054] Allocated trie memory caches             clean=154.00MiB dirty=256.00MiB
INFO [10-16|09:58:14.054] State schema set to default              scheme=path
WARN [10-16|09:58:14.055] Head block is not reachable
DEBUG[10-16|09:58:14.055] Current full block not old enough to freeze err="freezing threshold is not available"
INFO [10-16|09:58:14.055] Initialising Ethereum protocol           network=412,346 dbversion=<nil>
INFO [10-16|09:58:14.055] Load database journal from disk
INFO [10-16|09:58:14.056] State snapshot generator is not found
INFO [10-16|09:58:14.056] Starting snapshot generation             root=56e81f..63b421 accounts=0  slots=0     storage=0.00B   dangling=0 elapsed="3.066µs"
INFO [10-16|09:58:14.056] Initialized path database                triecache=154.00MiB statecache=102.00MiB buffer=256.00MiB state-history="last 90000 blocks"
INFO [10-16|09:58:14.056] Writing custom genesis block
--- FAIL: TestEthSyncing (22.43s)

TestTimeboostTxsTimeoutByBlock

Stack Traces | 41.110s run time

... [CONTENT TRUNCATED: Keeping last 20 lines]
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=16  size=3.29KiB   time="42.289µs"  gcnodes=938  gcsize=181.14KiB  gctime=2.551876ms  livenodes=145   livesize=28.88KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=24  size=4.59KiB   time="68.648µs"  gcnodes=962  gcsize=185.73KiB  gctime=2.620314ms  livenodes=121   livesize=24.29KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=18  size=3.56KiB   time="50.915µs"  gcnodes=980  gcsize=189.29KiB  gctime=2.671059ms  livenodes=103   livesize=20.73KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=18  size=3.53KiB   time="74.138µs"  gcnodes=998  gcsize=192.82KiB  gctime=2.744826ms  livenodes=85    livesize=17.20KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=17  size=3.40KiB   time="43.531µs"  gcnodes=1015 gcsize=196.22KiB  gctime=2.787806ms  livenodes=68    livesize=13.80KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=17  size=3.52KiB   time="45.174µs"  gcnodes=1032 gcsize=199.74KiB  gctime=2.83282ms   livenodes=51    livesize=10.28KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=16  size=3.24KiB   time="41.107µs"  gcnodes=1048 gcsize=202.98KiB  gctime=2.873786ms  livenodes=35    livesize=7.04KiB
DEBUG[10-16|10:00:05.464] Dereferenced trie from memory database   nodes=19  size=3.63KiB   time="46.788µs"  gcnodes=1067 gcsize=206.61KiB  gctime=2.920464ms  livenodes=16    livesize=3.41KiB
DEBUG[10-16|10:00:05.465] Dereferenced trie from memory database   nodes=16  size=3.41KiB   time="37.17µs"   gcnodes=1083 gcsize=210.02KiB  gctime=2.957514ms  livenodes=0     livesize=0.00B
DEBUG[10-16|10:00:05.465] Dereferenced trie from memory database   nodes=0   size=0.00B     time=171ns       gcnodes=1083 gcsize=210.02KiB  gctime=2.957604ms  livenodes=0     livesize=0.00B
DEBUG[10-16|10:00:05.465] Dereferenced trie from memory database   nodes=0   size=0.00B     time=211ns       gcnodes=1083 gcsize=210.02KiB  gctime=2.957705ms  livenodes=0     livesize=0.00B
INFO [10-16|10:00:05.465] Blockchain stopped
DEBUG[10-16|10:00:05.467] redis producer: check responses starting
DEBUG[10-16|10:00:05.467] checkResponses                           responded=0 errored=0 checked=0
TRACE[10-16|10:00:05.467] Refreshing our lock                      id=auctioneer-64dff666-1760608765320082670
TRACE[10-16|10:00:05.469] P2P networking is spinning down
INFO [10-16|10:00:05.471] Context done while waiting redis streams to be ready, failed to start
ERROR[10-16|10:00:05.471] Context closed, autonomous auctioneer shutting down
ERROR[10-16|10:00:05.472] Context closed, autonomous auctioneer shutting down
--- FAIL: TestTimeboostTxsTimeoutByBlock (41.11s)

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