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`nix develop` builds an environment derivation from the user's derivation and removes the output checks, which do not apply to the environment (NixOS#14306). With structured attrs it erases `outputChecks` from the parsed `__json` object. Since 6b92dd2 (NixOS#16374), parsing always keeps the original encoding in `StructuredAttrs::verbatim`, and `unparse` writes that encoding when it is set. So the erase has no effect, and the environment derivation keeps the checks of the original. A check such as `maxSize` then fails the environment build: error: path '/nix/store/…-hello-env' is too large at 112 bytes; limit is 1 bytes Reset `verbatim` after the erase, so that `unparse` encodes the modified object. The existing test did not catch this. It ran `nix develop` inside `[[ -z "$(...)" ]]`, and a failing command prints nothing, which passes. Assign the output first, and add a `maxSize` check that the environment cannot meet. Assisted-by: Claude Code (claude-opus-5-5)
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Motivation
nix developandnix print-dev-envkeep theoutputChecksof a structured-attrs derivation in the environment derivation, so a check such asmaxSizefails the environment build:develop.ccerasesoutputChecksfrom the parsed__jsonobject (#14306). Since 6b92dd2 (#16374, "No warn on non-canonical structured attrs"), parsing always keeps the original encoding inStructuredAttrs::verbatim, andunparsewrites that encoding when it is set, so the erase has no effect. No release has 6b92dd2 yet.Implementation
Reset
verbatimafter the erase.The existing test (#14312) did not catch this: it ran
[[ -z "$(nix develop …)" ]], and a failingnix developprints nothing, so the test passed. The test now assigns the output first, and the fixture addsmaxSize = 1, which the environment cannot meet. Without the fix,flakes/developfails with the error above; with it, it passes.Checks, run locally on this change over master 8c8e8b8:
pre-commit,rl-next, the util, store, expr, fetchers and flake unit tests,nix-functional-tests,daemonCompat,hydraJobs.clangTidy,componentTestswith clangStdenv and sanitizers, the Windows cross-build ofnix-util-tests,nix flake show --all-systems, andvmTestsplain and instrumented.hydraJobs.tests.cgroupsfails, as it does on master: since 31cca91, daemon build cgroups are created insidenix-daemon(a separate fix).For reviewing agents
verbatimonly for non-canonical encodings. 6b92dd2 (No warn on non-canonical structured attrs #16374) made it unconditional, which reached every derivation thatnix developreads from the store.develop.cc, not inStructuredAttrs.develop.ccis the only code that mutates a parsedStructuredAttrs(primops.ccbuilds fresh ones withoutverbatim). A setter that clearsverbatimwould be a larger API change for one caller.nix print-dev-env, the env.drvcontains"outputChecks":{"out":{"maxSize":1}}.develop.ccneeds the same reset.outputChecksis the only change it makes tostructuredAttrs; the otherverbatimusers are the parser,operator==andunparse.2.35-maintenance, so no release has the regression.Assisted-by: Claude Code (claude-opus-5-5).Made by Lillecarl and Claude Code together. The commit carries an
Assisted-by:trailer, asCONTRIBUTING.mdrequires.Add 👍 to pull requests you find important.
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