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Diffstat (limited to 'doc/manual/src')
-rw-r--r-- | doc/manual/src/SUMMARY.md.in | 1 | ||||
-rw-r--r-- | doc/manual/src/contributing/cli-guideline.md | 82 | ||||
-rw-r--r-- | doc/manual/src/release-notes/rl-2.14.md | 22 | ||||
-rw-r--r-- | doc/manual/src/release-notes/rl-next.md | 28 |
4 files changed, 117 insertions, 16 deletions
diff --git a/doc/manual/src/SUMMARY.md.in b/doc/manual/src/SUMMARY.md.in index b1c551969..964091285 100644 --- a/doc/manual/src/SUMMARY.md.in +++ b/doc/manual/src/SUMMARY.md.in @@ -67,6 +67,7 @@ - [CLI guideline](contributing/cli-guideline.md) - [Release Notes](release-notes/release-notes.md) - [Release X.Y (202?-??-??)](release-notes/rl-next.md) + - [Release 2.14 (2023-02-28)](release-notes/rl-2.14.md) - [Release 2.13 (2023-01-17)](release-notes/rl-2.13.md) - [Release 2.12 (2022-12-06)](release-notes/rl-2.12.md) - [Release 2.11 (2022-08-25)](release-notes/rl-2.11.md) diff --git a/doc/manual/src/contributing/cli-guideline.md b/doc/manual/src/contributing/cli-guideline.md index 01a1b1e73..e53d2d178 100644 --- a/doc/manual/src/contributing/cli-guideline.md +++ b/doc/manual/src/contributing/cli-guideline.md @@ -389,6 +389,88 @@ colors, no emojis and using ASCII instead of Unicode symbols). The same should happen when TTY is not detected on STDERR. We should not display progress / status section, but only print warnings and errors. +## Returning future proof JSON + +The schema of JSON output should allow for backwards compatible extension. This section explains how to achieve this. + +Two definitions are helpful here, because while JSON only defines one "key-value" +object type, we use it to cover two use cases: + + - **dictionary**: a map from names to value that all have the same type. In + C++ this would be a `std::map` with string keys. + - **record**: a fixed set of attributes each with their own type. In C++, this + would be represented by a `struct`. + +It is best not to mix these use cases, as that may lead to incompatibilities when the schema changes. For example, adding a record field to a dictionary breaks consumers that assume all JSON object fields to have the same meaning and type. + +This leads to the following guidelines: + + - The top-level (root) value must be a record. + + Otherwise, one can not change the structure of a command's output. + + - The value of a dictionary item must be a record. + + Otherwise, the item type can not be extended. + + - List items should be records. + + Otherwise, one can not change the structure of the list items. + + If the order of the items does not matter, and each item has a unique key that is a string, consider representing the list as a dictionary instead. If the order of the items needs to be preserved, return a list of records. + + - Streaming JSON should return records. + + An example of a streaming JSON format is [JSON lines](https://jsonlines.org/), where each line represents a JSON value. These JSON values can be considered top-level values or list items, and they must be records. + +### Examples + + +This is bad, because all keys must be assumed to be store implementations: + +```json +{ + "local": { ... }, + "remote": { ... }, + "http": { ... } +} +``` + +This is good, because the it is extensible at the root, and is somewhat self-documenting: + +```json +{ + "storeTypes": { "local": { ... }, ... }, + "pluginSupport": true +} +``` + +While the dictionary of store types seems like a very complete response at first, a use case may arise that warrants returning additional information. +For example, the presence of plugin support may be crucial information for a client to proceed when their desired store type is missing. + + + +The following representation is bad because it is not extensible: + +```json +{ "outputs": [ "out" "bin" ] } +``` + +However, simply converting everything to records is not enough, because the order of outputs must be preserved: + +```json +{ "outputs": { "bin": {}, "out": {} } } +``` + +The first item is the default output. Deriving this information from the outputs ordering is not great, but this is how Nix currently happens to work. +While it is possible for a JSON parser to preserve the order of fields, we can not rely on this capability to be present in all JSON libraries. + +This representation is extensible and preserves the ordering: + +```json +{ "outputs": [ { "outputName": "out" }, { "outputName": "bin" } ] } +``` + ## Dialog with the user CLIs don't always make it clear when an action has taken place. For every diff --git a/doc/manual/src/release-notes/rl-2.14.md b/doc/manual/src/release-notes/rl-2.14.md new file mode 100644 index 000000000..705c118bb --- /dev/null +++ b/doc/manual/src/release-notes/rl-2.14.md @@ -0,0 +1,22 @@ +# Release 2.14 (2023-02-28) + +* A new function `builtins.readFileType` is available. It is similar to + `builtins.readDir` but acts on a single file or directory. + +* In flakes, the `.outPath` attribute of a flake now always refers to + the directory containing the `flake.nix`. This was not the case for + when `flake.nix` was in a subdirectory of e.g. a Git repository. + The root of the source of a flake in a subdirectory is still + available in `.sourceInfo.outPath`. + +* In derivations that use structured attributes, you can now use `unsafeDiscardReferences` + to disable scanning a given output for runtime dependencies: + ```nix + __structuredAttrs = true; + unsafeDiscardReferences.out = true; + ``` + This is useful e.g. when generating self-contained filesystem images with + their own embedded Nix store: hashes found inside such an image refer + to the embedded store and not to the host's Nix store. + + This requires the `discard-references` experimental feature. diff --git a/doc/manual/src/release-notes/rl-next.md b/doc/manual/src/release-notes/rl-next.md index 7e8344e63..091d12b7e 100644 --- a/doc/manual/src/release-notes/rl-next.md +++ b/doc/manual/src/release-notes/rl-next.md @@ -1,22 +1,18 @@ # Release X.Y (202?-??-??) -* A new function `builtins.readFileType` is available. It is similar to - `builtins.readDir` but acts on a single file or directory. +* The special handling of an [installable](../command-ref/new-cli/nix.md#installables) with `.drv` suffix being interpreted as all of the given [store derivation](../glossary.md#gloss-store-derivation)'s output paths is removed, and instead taken as the literal store path that it represents. -* The `builtins.readDir` function has been optimized when encountering not-yet-known - file types from POSIX's `readdir`. In such cases the type of each file is/was - discovered by making multiple syscalls. This change makes these operations - lazy such that these lookups will only be performed if the attribute is used. - This optimization affects a minority of filesystems and operating systems. + The new `^` syntax for store paths introduced in Nix 2.13 allows explicitly referencing output paths of a derivation. + Using this is better and more clear than relying on the now-removed `.drv` special handling. -* In derivations that use structured attributes, you can now use `unsafeDiscardReferences` - to disable scanning a given output for runtime dependencies: - ```nix - __structuredAttrs = true; - unsafeDiscardReferences.out = true; + For example, + ```shell-session + $ nix path-info /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv ``` - This is useful e.g. when generating self-contained filesystem images with - their own embedded Nix store: hashes found inside such an image refer - to the embedded store and not to the host's Nix store. - This requires the `discard-references` experimental feature. + now gives info about the derivation itself, while + + ```shell-session + $ nix path-info /nix/store/gzaflydcr6sb3567hap9q6srzx8ggdgg-glibc-2.33-78.drv^* + ``` + provides information about each of its outputs. |