disable the jsonv2 GOEXPERIMENT - #130
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carole-lavillonniere
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August 31, 2026 10:15
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Go 1.27 enables the jsonv2 experiment by default, reimplementing encoding/json and making json.RawMessage an alias for jsontext.Value. The repo inherited this from #122, which bumped the go directive from 1.26.6 to 1.27.0 -- that directive is a minimum toolchain requirement, so GOTOOLCHAIN =auto then builds everything with go1.27 and its default experiments. This emulator serializes customer Lambda payloads, so swapping JSON implementation should be a deliberate, tested decision rather than a side effect of a toolchain bump. Pin it off for now. There is no GODEBUG opt-out -- jsonv2 is selected at compile time via build tags -- so it must be an environment variable. Exporting it from the Makefile covers local builds, the docker targets (which re-enter this Makefile in the container) and CI, which invokes only make targets. Fixes the localstack branch, red since Aug 22, without touching the upstream test that the experiment broke.
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Ci is red since Aug 22 (#122 → #127 all merged over a failing test suite).
This has been blocking the weekly RIE auto-release.
What happened
#122 was a one-line Renovate change:
go 1.26.6→go 1.27.0. That line is not a library version — it is a minimum toolchain requirement. WithGOTOOLCHAIN=auto, the go command then fetches and builds everything with go1.27, and Go 1.27 enables the jsonv2 GOEXPERIMENT by default.Under jsonv2,
encoding/jsondeclarestype RawMessage = jsontext.Valueinstead oftype RawMessage []byte. Verified — the toolchain is what decides, the language directive is irrelevant except that it selects the toolchain:json.RawMessageresolves tojson.RawMessagejsontext.Value1.26.6jsontext.ValueGOEXPERIMENT=nojsonv2json.RawMessageTODO
testin the branch ruleset (needs an admin of this repo) 🙏