Trial: revert breaking changes for 10.2.0 readiness

[cmcfarlen]

Status

Draft / discussion only — not proposed for merge as-is.

This branch is the output of a trial exercise to answer the question:
"How painful would it be to ship 10.2.0 from a master with all
backward-incompatible changes reverted?"

It builds cleanly. It is not a release candidate.

What's in here

13 reverts + 1 build-tooling fix:

#	PR	What	Why
1	#13090	Config reload error reporting	Depends on #12892 (in 11-Dev)
2	#13110	_reload directive	Depends on #12892
3	#13117	Cap TLS cert compression length	Depends on #13088
4	#13088	TLS Cert Compression (RFC 8879)	Depends on config/ssl_multicert.h (in 11-Dev #12755)
5	#13070	plugin.config → plugin.yaml	Incompatible-labeled; depends on config_result.h (in 11-Dev)
6	#13048	Coverity fix on storage	Depends on #13031
7	#13031	storage.config + volume.config → storage.yaml	Incompatible-labeled
8	#12998	Parallel SSL cert load	Depends on #12755 (in 11-Dev)
9	#12988	Publish remap table after initial load	Surface conflict on ReverseProxy.cc with #12997
10	#12997	remap.yaml support	Depends on ConfigRegistry from #12892 (in 11-Dev)
11	#12983	11-Dev merge (with -m 1)	Brings in #11135, #11157, #12670, #12755, #12892, #12896, etc.
12	#12913	Master-side bump to 11.0.0	Incompatible-labeled
13	#12404	cqssrt log field for TLS resumption	Restored function references m_http_sm which #13123 renamed to m_data
—	tools	Skip files staged for deletion in cmake-format.sh	Build-tooling fix, useful regardless

The last one is a real upstream improvement worth landing on its own;
the rest are trial exploration.

What this trial proved

• The mechanical revert path is tractable with the right dependency order.
  v1 of this trial took ~2.5 hours and didn't finish (failed to build); v2
  with the dependency chain mapped took ~90 minutes and builds cleanly.
• The realistic cost is 1–2 days of focused work for production, not
  the 1–2 weeks initially feared.
• The dominant cost is not technical — it's the contributor
  conversations about deferred features (ATS Configuration Reload with observability/tracing - Token model #12892, plugin.config to plugin.yaml migration.  #13070, Support remap.yaml #12997, Add support for TLS Certificate Compression (RFC 8879) #13088,
  Parallell ssl cert load #12998 are all significant work).

What this trial does NOT prove

• Tests have not been run on this branch.
• Three months of Incompatible-tagged + un-tagged behavior changes
  exist on master that may not be captured here.
• This branch loses several useful features (plugin.yaml, remap.yaml,
  TLS cert compression, parallel SSL cert load, the new config-reload
  framework). Production would need to decide which to defer to 11.0.0
  and which to re-implement compat-friendly versions of for 10.2.0.

Detailed notes

See the comment below for the full execution log including conflict
resolution decisions, build verification, and effort breakdown.

🤖 Generated with Claude Code

[cmcfarlen]

Trial Revert v2 — Notes

Companion log for revert-incompat-plan-v2.md. Each section captures one
revert step on branch revert-incompat-trial-v2.

Setup

• Source branch: upstream/master
• Source HEAD: 09c4f8a125 (Enable code review settings in .asf.yaml, Enable code review settings in .asf.yaml #13183)
• Trial branch: revert-incompat-trial-v2
• Plan: 11 reverts, dependency-aware order, pre-emptive LogAccess
  fix-up after 11-Dev revert.

Reverts

Step 1–4: Config-reload + TLS-cert-compression dependents

Step	PR	Commit	Result
1	#13090	4645b7dcb3	clean, 43 files / +227 -903
2	#13110	34790b0a9d	clean, 10 files / +11 -657
3	#13117	4f1d3594dd	clean, 4 files / -27
4	#13088	b98d8d0b31	clean (large; deletes TLS cert compression infra)

Step 5: #13070 plugin.yaml migration

Commit	49d109470b
Result	clean (was 6 conflicts in v1; the dependent reverts cleared the path)

Step 6–7: Storage migration chain

Step	PR	Commit	Result
6	#13048	9828150402	clean, 3 files
7	#13031	6d32974095	clean (was 5 conflicts in v1; #13048 + #13070 reverts already removed)

Step 8: #12998 Parallel SSL cert load

Commit	e5136dde5b
Result	clean, 8 files (auto-merged records.yaml docs, RecordsConfig.cc, SSLConfig.cc)

Step 9: #12988 + #12997 — surface conflict on ReverseProxy.cc

Initially attempted git revert #12997 directly. Hit:

• 1 content conflict in ReverseProxy.cc
• 10 modify/delete conflicts on tests/gold_tests/remap_yaml/*.yaml files (added by Support remap.yaml #12997, modified by Proxy Verifier: use concise stack protocol specification #13003 "Proxy Verifier: use concise stack protocol")

Aborted, added #12988 ("Publish remap table after initial load") to the
revert list. #12988 is not incompatible — it's a compat improvement —
but it touched the same init_reverse_proxy() block as #12997, creating a
surface-level conflict.

Revert order: #12988 → #12997. Both clean after that.

Step	PR	Commit
9a	#12988	f0b3be46b7
9b	#12997	8ef420635d

Step 10: 11-Dev merge (#12983)

Commit	30a01d6e41
Result	9 conflicts (down from 17 in v1 — dependent reverts cleared most surfaces)

Conflict resolution:

• Manual: Filenames.h, hostdb/CMakeLists.txt (kept Relocate HostDB tests and benchmark to standard directories #13115 add_subdirectory(unit_tests)), records/CMakeLists.txt (kept only test_RecDumpRecords.cc), P_SSLConfig.h (restored session-cache fields).
• --theirs: SSLUtils.cc (tightly coupled to ssl_multicert.yaml), 4× gold tests.
• git rm: 1 UD file (negative-caching-malformed-cc.replay.yaml).

Step 11: #12913 master-side version bump

Commit	f0f4f16149
Result	clean, 1 line

Step 12 (added during execution): #12404 cqssrt log field

After 11-Dev revert, the restored marshal_client_ssl_resumption_type
function referenced m_http_sm, which #13123 (kept on master, in 10.2.x as
#13124) renamed to m_data. v1 fixed this with a fixup commit; v2 instead
reverts the original PR (#12404) for cleanliness.

Commit	26cafc24d2
Result	clean, 5 files / +3 -49

#12404 is in both master and 10.2.x (pre-divergence). Reverting it on
the trial branch is safe; reverting it in production would require also
removing the cqssrt log field from 10.2.x (out of scope for the trial).

Step 13 (incidental): cmake-format.sh fix

Format hook hung because git ls-tree -r HEAD listed
src/config/CMakeLists.txt (which had been deleted by an earlier revert)
and cmake-format raised FileNotFoundError. Patched the script to
filter out files staged for deletion via
git diff --cached --name-only --diff-filter=D.

Commit	3a8d37117b
Status	useful for upstream — not a revert

Build verification

$ cmake --build build-mydev
[265/266] Linking CXX executable src/traffic_server/traffic_server
$ echo $?
0

traffic_server binary built cleanly (18 MB). Some ld: warning: ignoring duplicate libraries are present but cosmetic, not errors.

Final state vs upstream/10.2.x

• 261 commits on trial-v2 not on 10.2.x (master-additive PRs that survived)
• 98 commits on 10.2.x not on trial-v2 (10.2.x branch-specific work)
• 507 files changed, +15,778 / -3,869 lines

v2 verdict: how painful, with lessons applied?

Mechanical effort once dependencies were known: ~90 minutes total.
13 reverts including the two discovered during execution (#12988, #12404).

Cost categories that v1 surfaced and v2 confirmed:

1. Direct conflicts — small. Replace storage.config and volume.config with storage.yaml #13031 had 0 conflicts in v2 vs 5 in v1
   once the dependent reverts (plugin.config to plugin.yaml migration.  #13070, Fix Coverity 1646593-1646605 #13048) ran first. The 11-Dev
   merge had 9 conflicts vs 17 in v1.
2. Dependency-chain reverts — predictable but additive. The plan
   identified 7 dependents up front. One more (Publish remap table after initial load #12988) surfaced as a
   surface conflict during execution.
3. Silent post-merge dependencies — eliminated by reverting Add support for TLS Certificate Compression (RFC 8879) #13088,
   Parallell ssl cert load #12998, Support remap.yaml #12997 before the 11-Dev merge. The build went clean on
   first attempt afterward.
4. cqssrt log field for TLS resumption type #12404-style "old PR uses now-renamed member" — predicted, found.
   Pre-emptive fix-up was in the plan; user preferred clean revert
   instead of fix-up.

Revised effort estimate for production:

• v1 estimate was 3–5 days optimistic / 1–2 weeks realistic.
• v2 result: with dependency map in hand, the mechanical work is
  tractable in a single afternoon. 1–2 days realistic for someone
  who can review the plan and resolve conflicts confidently.
• The remaining cost is social, not mechanical: 13 reverts means 13
  contributor conversations about dropped/deferred features. Several of
  the reverted PRs (ATS Configuration Reload with observability/tracing - Token model #12892, plugin.config to plugin.yaml migration.  #13070, Support remap.yaml #12997, Add support for TLS Certificate Compression (RFC 8879) #13088, Parallell ssl cert load #12998) are
  significant work that authors will want re-landed once 10.2.0 ships.

Trial branch state at completion

• Branch: revert-incompat-trial-v2
• HEAD: 3a8d37117b (cmake-format.sh fix)
• Build: clean ✓
• Notes file and plan are uncommitted (intentional; trial artifacts)