Limitations & Not Planned

Limitations

Every top-level key in a config file must be a table, with one exception: $schema, so a JSON file can point at the schema that describes it. Sections are figment profiles and a profile has to be a map, so a stray "_comment": "..." at the top level is an error — one that now names the key and says why.
TOML datetimes are not modelled and deserialize as a table.
The macro refers to the crate as ::dynamic_config, so renaming the dependency is not supported.
Error messages name the environment prefix rather than the exact variable, because that is the granularity figment reports.

Not planned

Each of these is a real request with a real answer. They are refused rather than unbuilt, so that nobody spends an afternoon discovering the reason — and each says what would reopen it.

figment's profiles are a general mechanism. This crate spends them on sections — key = "db" selects the db profile — and re-implements the profile idea on top with profile_env and sibling files (config.production.toml). So a provider handed to Source::provider cannot carry its own profiles through.

The difficulty is not any one part; it is that select(key), the section mapping, profile_env, sibling files, check(), source_of and every diagnostic that names a section all assume the current arrangement. Changing it means giving sections a different mechanism and rewriting the layering underneath everything that reads well today.

What would reopen it: a figment provider whose own profiles you need, where Source::provider plus profile_env genuinely cannot express what you are after.

Case-insensitive keys

Viper lowercases everything. It hides typos — Prot and port become the same key, so unknown-key detection can never tell you about the first — and it cannot round-trip: a configuration read and written back comes out in different case from the one a person wrote.

What would reopen it: nothing. This one is a principle rather than a cost.

HCL, Java properties, INI

Each is a parser and a set of edge cases for a format nobody here has asked for, and none of them is something figment provides.

The answer that is not a fork: Source::provider takes any figment provider, so a crate that parses one of these wires in without this one growing a dependency.

Independent instances

Viper needs them because its default instance is a global. Here every configuration type already has its own storage, keyed by the type — the same isolation without the bookkeeping.

Inferring a type from a default value

serde already knows the type. Viper's SetTypeByDefaultValue exists because Go's map[string]interface{} does not.

A service-account JSON key for Firestore

Signing one means an RS256 stack inside a configuration library, and Google's own guidance is that a downloaded key is the option of last resort. Workload identity covers GKE, Cloud Run, GCE and Cloud Functions; anything else can mint a token outside the process and pass it in.

Roadmap

ROADMAP.md is what might still be built, and why each item is not obvious. It is short on purpose.

dynamic-config