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4
doc/manual/source/advanced-topics/distributed-builds.md
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@ -20,7 +20,7 @@ For a local machine to forward a build to a remote machine, the remote machine m
## Testing
To test connecting to a remote Nix instance (in this case `mac`), run:
To test connecting to a remote [Nix instance] (in this case `mac`), run:
```console
nix store info --store ssh://username@mac
@ -106,3 +106,5 @@ file included in `builders` via the syntax `@/path/to/file`. For example,
causes the list of machines in `/etc/nix/machines` to be included.
(This is the default.)
[Nix instance]: @docroot@/glossary.md#gloss-nix-instance

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doc/manual/source/glossary.md
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@ -1,5 +1,13 @@
# Glossary
- [build system]{#gloss-build-system}
Generic term for software that facilitates the building of software by automating the invocation of compilers, linkers, and other tools.
Nix can be used as a generic build system.
It has no knowledge of any particular programming language or toolchain.
These details are specified in [derivation expressions](#gloss-derivation-expression).
- [content address]{#gloss-content-address}
A
@ -19,6 +27,10 @@
Besides content addressing, the Nix store also uses [input addressing](#gloss-input-addressed-store-object).
- [content-addressed storage]{#gloss-content-addressed-store}
The industry term for storage and retrieval systems using [content addressing](#gloss-content-address). A Nix store also has [input addressing](#gloss-input-addressed-store-object), and metadata.
- [store derivation]{#gloss-store-derivation}
A single build task.
@ -88,6 +100,12 @@
[store]: #gloss-store
- [Nix instance]{#gloss-nix-instance}
<!-- ambiguous -->
1. An installation of Nix, which includes the presence of a [store], and the Nix package manager which operates on that store.
A local Nix installation and a [remote builder](@docroot@/advanced-topics/distributed-builds.md) are two examples of Nix instances.
2. A running Nix process, such as the `nix` command.
- [binary cache]{#gloss-binary-cache}
A *binary cache* is a Nix store which uses a different format: its
@ -220,7 +238,7 @@
directly or indirectly “reachable” from that store path; that is,
it’s the closure of the path under the *references* relation. For
a package, the closure of its derivation is equivalent to the
build-time dependencies, while the closure of its output path is
build-time dependencies, while the closure of its [output path] is
equivalent to its runtime dependencies. For correct deployment it
is necessary to deploy whole closures, since otherwise at runtime
files could be missing. The command `nix-store --query --requisites ` prints out

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doc/manual/source/protocols/store-path.md
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@ -53,7 +53,7 @@ where
method of content addressing store objects,
if the hash algorithm is [SHA-256].
Just like in the "Text" case, we can have the store objects referenced by their paths.
Additionally, we can have an optional `:self` label to denote self reference.
Additionally, we can have an optional `:self` label to denote self-reference.
- ```ebnf
| "output:" id

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doc/manual/source/store/building.md
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@ -54,7 +54,7 @@ The [`builder`](./derivation/index.md#builder) is executed as follows:
it’s `out`.)
- If an output path already exists, it is removed. Also, locks are
acquired to prevent multiple Nix instances from performing the same
acquired to prevent multiple [Nix instances][Nix instance] from performing the same
build at the same time.
- A log of the combined standard output and error is written to
@ -95,3 +95,6 @@ If the builder exited successfully, the following steps happen in order to turn
Nix also scans for references to other outputs' paths in the same way, because outputs are allowed to refer to each other.
If the outputs' references to each other form a cycle, this is an error, because the references of store objects much be acyclic.
[Nix instance]: @docroot@/glossary.md#gloss-nix-instance

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doc/manual/source/store/derivation/index.md
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@ -1,7 +1,7 @@
# Store Derivation and Deriving Path
Besides functioning as a [content addressed store] the Nix store layer works as a [build system].
Other system (like Git or IPFS) also store and transfer immutable data, but they don't concern themselves with *how* that data was created.
Besides functioning as a [content-addressed store], the Nix store layer works as a [build system].
Other systems (like Git or IPFS) also store and transfer immutable data, but they don't concern themselves with *how* that data was created.
This is where Nix distinguishes itself.
*Derivations* represent individual build steps, and *deriving paths* are needed to refer to the *outputs* of those build steps before they are built.
@ -42,6 +42,8 @@ A derivation consists of:
[args]: #args
[env]: #env
[system]: #system
[content-addressed store]: @docroot@/glossary.md#gloss-content-addressed-store
[build system]: @docroot@/glossary.md#gloss-build-system
### Referencing derivations {#derivation-path}
@ -78,7 +80,7 @@ type DerivingPath = ConstantPath | OutputPath;
```
Deriving paths are necessary because, in general and particularly for [content-addressing derivations][content-addressing derivation], the [store path] of an [output] is not known in advance.
We can use an output deriving path to refer to such an out, instead of the store path which we do not yet know.
We can use an output deriving path to refer to such an output, instead of the store path which we do not yet know.
[deriving path]: #deriving-path
[validity]: @docroot@/glossary.md#gloss-validity
@ -89,25 +91,26 @@ A derivation is constructed from the parts documented in the following subsectio
### Inputs {#inputs}
The inputs are a set of [deriving paths][deriving path], refering to all store objects needed in order to perform this build step.
The inputs are a set of [deriving paths][deriving path], referring to all store objects needed in order to perform this build step.
The [process creation fields] will presumably include many [store paths][store path]:
- The path to the executable normally starts with a store path
- The arguments and environment variables likely contain many other store paths.
But rather than somehow scanning all the other fields for inputs, Nix requires that all inputs be explicitly collected in the inputs field. It is instead the responsibility of the creator of a derivation (e.g. the evaluator) to ensure that every store object referenced in another field (e.g. referenced by store path) is included in this inputs field.
But rather than somehow scanning all the other fields for inputs, Nix requires that all inputs be explicitly collected in the inputs field. It is instead the responsibility of the creator of a derivation (e.g. the evaluator) to ensure that every store object referenced in another field (e.g. referenced by store path) is included in this inputs field.
### System {#system}
The system type on which the [`builder`](#attr-builder) executable is meant to be run.
A necessary condition for Nix to schedule a given derivation on some Nix instance is for the "system" of that derivation to match that instance's [`system` configuration option].
A necessary condition for Nix to schedule a given derivation on some [Nix instance] is for the "system" of that derivation to match that instance's [`system` configuration option] or [`extra-platforms` configuration option].
By putting the `system` in each derivation, Nix allows *heterogenous* build plans, where not all steps can be run on the same machine or same sort of machine.
Nix can schedule builds such that it automatically builds on other platforms by [forwarding build requests](@docroot@/advanced-topics/distributed-builds.md) to other Nix instances.
[`system` configuration option]: @docroot@/command-ref/conf-file.md#conf-system
[`extra-platforms` configuration option]: @docroot@/command-ref/conf-file.md#conf-extra-platforms
[content-addressing derivation]: @docroot@/glossary.md#gloss-content-addressing-derivation
[realise]: @docroot@/glossary.md#gloss-realise
@ -240,14 +243,14 @@ That works because we've implicitly assumed that all derivations are created *st
But what if derivations could also be created dynamically within Nix?
In other words, what if derivations could be the outputs of other derivations?
:::{.note}
In the parlance of "Build Systems à la carte", we are generalizing the Nix store layer to be a "Monadic" instead of "Applicative" build system.
:::
> **Note**
>
> In the parlance of "Build Systems à la carte", we are generalizing the Nix store layer to be a "Monadic" instead of "Applicative" build system.
How should we refer to such derivations?
A deriving path works, the same as how we refer to other derivation outputs.
But what about a dynamic derivations output?
(i.e. how do we refer to the output of an output of a derivation?)
(i.e. how do we refer to the output of a derivation, which is itself an output of a derivation?)
For that we need to generalize the definition of deriving path, replacing the store path used to refer to the derivation with a nested deriving path:
```diff
@ -295,3 +298,5 @@ The result of this is that it is possible to have a chain of `^<output-name>` at
> |------------------------------------------------------------| |-----|
> innermost constant store path (usual encoding) output name
> ```
[Nix instance]: @docroot@/glossary.md#gloss-nix-instance

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doc/manual/source/store/derivation/outputs/content-address.md
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@ -12,7 +12,7 @@ Given the method, the output's name (computed from the derivation name and outpu
## Fixed-output content-addressing {#fixed}
In this case the content-address of the *fixed* in advanced by the derivation itself.
In this case the content address of the *fixed* in advanced by the derivation itself.
In other words, when the derivation has finished [building](@docroot@/store/building.md), and the provisional output' content-address is computed as part of the process to turn it into a *bona fide* store object, the calculated content address must much that given in the derivation, or the build of that derivation will be deemed a failure.
The output spec for an output with a fixed content addresses additionally contains:
@ -159,7 +159,7 @@ A *determinstic* content-addressing derivation should produce outputs with the s
### Floating versus Fixed
While the destinction between content- and input-addressing is one of *mechanism*, the distinction between fixed and floating content addression is more one of *policy*.
While the distinction between content- and input-addressing is one of *mechanism*, the distinction between fixed and floating content addressing is more one of *policy*.
A fixed output that passes its content address check is just like a floating output.
It is only in the potential for that check to fail that they are different.

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doc/manual/source/store/derivation/outputs/input-address.md
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@ -3,7 +3,7 @@
[input addressing]: #input-addressing
"Input addressing" means the address the store object by the *way it was made* rather than *what it is*.
That is to say, an input-addressed output's store path is a function not of the output itself, but the derivation that produced it.
That is to say, an input-addressed output's store path is a function not of the output itself, but of the derivation that produced it.
Even if two store paths have the same contents, if they are produced in different ways, and one is input-addressed, then they will have different store paths, and thus guaranteed to not be the same store object.
<!---

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doc/manual/source/store/store-object/content-address.md
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@ -28,7 +28,7 @@ With all currently-supported store object content-addressing methods, the file s
### References
#### References to other store object#### References to other store objectss
#### References to other store objects
With all currently supported store object content addressing methods,
other objects are referred to by their regular (string-encoded-) [store paths][Store Path].
@ -44,28 +44,28 @@ Self-references however cannot be referred to by their path, because we are in t
> which is computationally infeasible.
> As far as we know, this is equivalent to finding a hash collision.
Instead we have a "has self reference" boolean, which end up affecting the digest:
In all currently-supported store object content-addressing methods, when hashing the file system object data, any occurence of store objects own store path in the digested data is replaced with a [sentinal value](https://en.wikipedia.org/wiki/Sentinel_value).
Instead we have a "has self-reference" boolean, which ends up affecting the digest:
In all currently-supported store object content-addressing methods, when hashing the file system object data, any occurence of store object's own store path in the digested data is replaced with a [sentinel value](https://en.wikipedia.org/wiki/Sentinel_value).
The hashes of these modified input streams are used instead.
When validating the content-address of a store object after the fact, the above process works as written.
When validating the content address of a store object after the fact, the above process works as written.
However, when first creating the store object we don't know the store object's store path, as explained just above.
We therefore, strictly speaking, do not know what value we will be replacing with the sentinental value in the inputs to hash functions.
What instead happens is that the provisional store object --- the data from which we wish to create a store object --- is paired with a provisional "scratch" store path (that presumably was choosen when the data was created).
That provisional store path is instead what is replaced with the sentinal value, rather than the final store object which we do not yet know.
What instead happens is that the provisional store object --- the data from which we wish to create a store object --- is paired with a provisional "scratch" store path (that presumably was chosen when the data was created).
That provisional store path is instead what is replaced with the sentinel value, rather than the final store object which we do not yet know.
> **Design note**
>
> It is an informal property of content-addressed store objects that the choice of provisional store path should not matter.
> In other words, if a provisional store object is prepared in the same way except for the choice of provision store path, the provisional data need not be identical.
> But, after the sentinal value is substituted in place of each provisional store object's provision store path, the final so-normalized data *should* be identifical.
> But, after the sentinel value is substituted in place of each provisional store object's provision store path, the final so-normalized data *should* be identical.
>
> If, conversely, the data after this normalization process is still different, we'll compute a different content-address.
> The method of preparing the provisional self-referenced data has *failed* to be deterministic in the sense of not *leaking* the choice of provisional store path --- a choice which is supposed to be arbitrary --- into the final store object.
>
> This property is informal because at this stage, we are just described store objects, which have no formal notion of their origin.
> Without such a formal notion, there is nothing to formally accuse of being insufficiently deterministic.
> Later in this chapter, when we cover [derivations](@docroot@/store/derivation/index.md), we will have a chance to make this a formal property, not of content-addressed store objects themselves, but of derivations that *produce* content-addressed store objects.
> Where we cover [derivations](@docroot@/store/derivation/index.md), we will have a chance to make this a formal property, not of content-addressed store objects themselves, but of derivations that *produce* content-addressed store objects.
### Name and Store Directory
@ -88,7 +88,7 @@ References are not supported: store objects with flat hashing *and* references c
This also uses the corresponding [Flat](../file-system-object/content-address.md#serial-flat) method of file system object content addressing.
References to other store objects are supported, but self references are not.
References to other store objects are supported, but self-references are not.
This is the only store-object content-addressing method that is not named identically with a corresponding file system object method.
It is somewhat obscure, mainly used for "drv files"
@ -99,7 +99,7 @@ Prefer another method if possible.
This uses the corresponding [Nix Archive](../file-system-object/content-address.md#serial-nix-archive) method of file system object content addressing.
References (to other store objects and self references alike) are supported so long as the hash algorithm is SHA-256, but not (neither kind) otherwise.
References (to other store objects and self-references alike) are supported so long as the hash algorithm is SHA-256, but not (neither kind) otherwise.
### Git { #method-git }