Template Function Coverage

This page tracks which template functions jhelm implements relative to upstream Go text/template, Sprig, and Helm, and flags functions that are present but only partially faithful ("partial") so chart authors know where behaviour may diverge from Go Helm.

Baseline: the locally installed helm binary used by the comparison test suite (Helm 3.19 / Sprig as vendored by that release). Verified by enumerating jhelm’s registered functions and probing each candidate against helm template.

1. Summary

Group Status Notes

Go text/template builtins

✅ Complete (19 / 19)

and or not eq ne lt le gt ge · index slice len call · print printf println · html js urlquery

Sprig functions

✅ Complete

All documented Sprig categories are registered (strings, math, lists, dicts, dates, encoding, crypto, semver, reflection, paths, regex, defaults, type conversion, URL, UUID, network). env / expandenv are intentionally omitted to match Helm’s security removal.

Helm functions

✅ Complete

include tpl required lookup · all toYaml/fromYaml, toJson/fromJson, toToml/fromToml (+ must*) present. toYamlPretty was the last gap and is now implemented.

2. Genuinely missing

None. toYamlPretty (Helm’s indented-sequence YAML marshaller — block sequence items indented under their key, ` - x` instead of - x) was the only gap and has been added.

Earlier audits circulated a list of "Helm 4 duration helpers" (durationSeconds, durationMinutes, durationRoundTo, mustToDuration, …). These are not real Helm functions — every one returns function "…" not defined from helm template. They are not tracked as gaps. jhelm does implement the real Sprig duration functions: duration and durationRound.

3. Partial / verify (present, but behaviour may diverge)

These functions are registered and work, but a JVM reimplementation cannot always reproduce Go’s exact output. Treat output as structurally correct, not byte-identical, unless a parity test exists.

Function(s) Caveat

lookup

Queries the Kubernetes API. Returns an empty map when no KubernetesProvider is wired (the default, and the behaviour of helm template without a cluster). Live-cluster results require jhelm-kube.

kubeVersion

Returns a stub (v1.28.0) when no provider is available.

getHostByName

Performs real DNS resolution; result is environment-dependent and non-deterministic, like Helm.

genCA, genCAWithKey, genSelfSignedCert*, genSignedCert*, genPrivateKey, buildCustomCert

X.509 / key PEM encoding, serial numbers, and validity defaults can differ from Go’s crypto/x509. Output is not byte-stable across runs (fresh keys), so only structural use is portable.

bcrypt, htpasswd, derivePassword

Salted / algorithm-specific output. Verify the hash prefix and format match; exact values are non-deterministic.

encryptAES, decryptAES

Round-trips within jhelm, but cross-compatibility with Helm-produced ciphertext depends on identical key derivation and framing.

semverCompare

Masterminds constraint grammar (`^ ~ - x

>=`, pre-release precedence). Edge cases may differ from the underlying Java semver handling.

toToml, fromToml (+ must*)

TOML key ordering, datetime, and nested-table emission vary by library; round-trips and string comparisons are fragile.

randAlpha, randAlphaNum, randAscii, randNumeric, randBytes, randInt, uuidv4, shuffle

Inherently non-deterministic; jhelm’s PRNG does not reproduce Go’s sequence. Only length / charset / format are guaranteed.

4. jhelm extensions (non-standard)

jhelm registers a few functions that are not in upstream Sprig or Helm. They are harmless convenience aliases, but a chart relying on them is not portable to real Helm:

  • mustHasKey, mustKeys, mustValues, mustPick, mustOmit — must* aliases of the Sprig dict functions (Sprig has only the non-must forms).

  • mustInclude, mustTpl, mustFromYaml, mustFromYamlArray, mustFromJsonArray, mustFromToml — must* aliases not present in Helm.

  • kubeVersion — exposed as a function; Helm exposes this via the .Capabilities.KubeVersion object instead.

5. Known template-engine limitations

Beyond the function map, the most common "it works in Helm but not jhelm" cases are engine/edge-case behaviours rather than missing functions. Known and fixed items (see git history / issues):

  • tpl of a string that both define`s and `include`s a template in one string — fixed (defines declared inside `tpl content are now registered in the shared namespace).

  • toYaml of a string containing " inside a sequence item produced \"-escaped output that broke a subsequent tpl(toYaml …) — fixed (sequence items are normalised to plain scalars).

  • Large umbrella charts exhausted the heap due to exponential template-alias growth — fixed.

Open / under investigation:

  • Nested tpl (a tpl call whose rendered output contains another tpl) can still fail to parse on some charts (e.g. grafana/loki loki.calculatedConfig).

6. References