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Make the Derived Path family of types inductive for dynamic derivations

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We want to be able to write down `foo.drv^bar.drv^baz`:
`foo.drv^bar.drv` is the dynamic derivation (since it is itself a
derivation output, `bar.drv` from `foo.drv`).

To that end, we create `Single{Derivation,BuiltPath}` types, that are
very similar except instead of having multiple outputs (in a set or
map), they have a single one. This is for everything to the left of the
rightmost `^`.

`NixStringContextElem` has an analogous change, and now can reuse
`SingleDerivedPath` at the top level. In fact, if we ever get rid of
`DrvDeep`, `NixStringContextElem` could be replaced with
`SingleDerivedPath` entirely!

Important note: some JSON formats have changed.

We already can *produce* dynamic derivations, but we can't refer to them
directly. Today, we can merely express building or example at the top
imperatively over time by building `foo.drv^bar.drv`, and then with a
second nix invocation doing `<result-from-first>^baz`, but this is not
declarative. The ethos of Nix of being able to write down the full plan
everything you want to do, and then execute than plan with a single
command, and for that we need the new inductive form of these types.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
This commit is contained in:
John Ericson 2023-01-15 17:39:04 -05:00
parent d00fe5f225
commit 60b7121d2c
48 changed files with 1136 additions and 267 deletions
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21
src/libexpr/value/context.hh
View file

@ -3,7 +3,7 @@
#include "util.hh"
#include "comparator.hh"
#include "path.hh"
#include "derived-path.hh"
#include <variant>
@ -31,11 +31,7 @@ public:
*
* Encoded as just the path: ‘<path>’.
*/
struct NixStringContextElem_Opaque {
StorePath path;
GENERATE_CMP(NixStringContextElem_Opaque, me->path);
};
typedef SingleDerivedPath::Opaque NixStringContextElem_Opaque;
/**
* Path to a derivation and its entire build closure.
@ -57,12 +53,7 @@ struct NixStringContextElem_DrvDeep {
*
* Encoded in the form ‘!<output>!<drvPath>’.
*/
struct NixStringContextElem_Built {
StorePath drvPath;
std::string output;
GENERATE_CMP(NixStringContextElem_Built, me->drvPath, me->output);
};
typedef SingleDerivedPath::Built NixStringContextElem_Built;
using _NixStringContextElem_Raw = std::variant<
NixStringContextElem_Opaque,
@ -93,8 +84,12 @@ struct NixStringContextElem : _NixStringContextElem_Raw {
* - ‘<path>’
* - ‘=<path>’
* - ‘!<name>!<path>’
*
* @param xpSettings Stop-gap to avoid globals during unit tests.
*/
static NixStringContextElem parse(std::string_view s);
static NixStringContextElem parse(
std::string_view s,
const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
std::string to_string() const;
};