Add parseFlakeRef and flakeRefToString builtins (#8670)

Over the last year or so I've run into several use cases where I need to
parse and/or serialize URLs for use by `builtins.fetchTree` or
`builtins.getFlake`, largely in order to produce _lockfile-like_ files
for lang2nix frameworks or tools which use `nix` internally to drive
builds.

I've gone through the painstaking process of emulating
`nix::FlakeRef::fromAttrs` and `nix::parseFlakeRef` several times with
mixed success; but these are difficult to create and even harder to
maintain if I hope to stay aligned with changes to the real
parser/serializer.

I understand why adding new `builtins` isn't something we want to do
flagrantly. I'm recommending this addition simply because I keep
encountering use cases where I need to parse/serialize these URIs in
`nix` expressions, and I want a reliable solution.

Co-authored-by: Eelco Dolstra <edolstra@gmail.com>
Co-authored-by: John Ericson <git@JohnEricson.me>
This commit is contained in:
Alex Ameen 2023-07-25 12:43:33 -05:00 committed by GitHub
parent 484c820c48
commit 2d1d81114d
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6 changed files with 112 additions and 0 deletions

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@ -1 +1,8 @@
# Release X.Y (202?-??-??) # Release X.Y (202?-??-??)
- Two new builtin functions,
[`builtins.parseFlakeRef`](@docroot@/language/builtins.md#builtins-parseFlakeRef)
and
[`builtins.flakeRefToString`](@docroot@/language/builtins.md#builtins-flakeRefToString),
have been added.
These functions are useful for converting between flake references encoded as attribute sets and URLs.

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@ -793,6 +793,101 @@ static RegisterPrimOp r2({
.experimentalFeature = Xp::Flakes, .experimentalFeature = Xp::Flakes,
}); });
static void prim_parseFlakeRef(
EvalState & state,
const PosIdx pos,
Value * * args,
Value & v)
{
std::string flakeRefS(state.forceStringNoCtx(*args[0], pos,
"while evaluating the argument passed to builtins.parseFlakeRef"));
auto attrs = parseFlakeRef(flakeRefS, {}, true).toAttrs();
auto binds = state.buildBindings(attrs.size());
for (const auto & [key, value] : attrs) {
auto s = state.symbols.create(key);
auto & vv = binds.alloc(s);
std::visit(overloaded {
[&vv](const std::string & value) { vv.mkString(value); },
[&vv](const uint64_t & value) { vv.mkInt(value); },
[&vv](const Explicit<bool> & value) { vv.mkBool(value.t); }
}, value);
}
v.mkAttrs(binds);
}
static RegisterPrimOp r3({
.name = "__parseFlakeRef",
.args = {"flake-ref"},
.doc = R"(
Parse a flake reference, and return its exploded form.
For example:
```nix
builtins.parseFlakeRef "github:NixOS/nixpkgs/23.05?dir=lib"
```
evaluates to:
```nix
{ dir = "lib"; owner = "NixOS"; ref = "23.05"; repo = "nixpkgs"; type = "github"; }
```
)",
.fun = prim_parseFlakeRef,
.experimentalFeature = Xp::Flakes,
});
static void prim_flakeRefToString(
EvalState & state,
const PosIdx pos,
Value * * args,
Value & v)
{
state.forceAttrs(*args[0], noPos,
"while evaluating the argument passed to builtins.flakeRefToString");
fetchers::Attrs attrs;
for (const auto & attr : *args[0]->attrs) {
auto t = attr.value->type();
if (t == nInt) {
attrs.emplace(state.symbols[attr.name],
(uint64_t) attr.value->integer);
} else if (t == nBool) {
attrs.emplace(state.symbols[attr.name],
Explicit<bool> { attr.value->boolean });
} else if (t == nString) {
attrs.emplace(state.symbols[attr.name],
std::string(attr.value->str()));
} else {
state.error(
"flake reference attribute sets may only contain integers, Booleans, "
"and strings, but attribute '%s' is %s",
state.symbols[attr.name],
showType(*attr.value)).debugThrow<EvalError>();
}
}
auto flakeRef = FlakeRef::fromAttrs(attrs);
v.mkString(flakeRef.to_string());
}
static RegisterPrimOp r4({
.name = "__flakeRefToString",
.args = {"attrs"},
.doc = R"(
Convert a flake reference from attribute set format to URL format.
For example:
```nix
builtins.flakeRefToString {
dir = "lib"; owner = "NixOS"; ref = "23.05"; repo = "nixpkgs"; type = "github";
}
```
evaluates to
```nix
"github:NixOS/nixpkgs/23.05?dir=lib"
```
)",
.fun = prim_flakeRefToString,
.experimentalFeature = Xp::Flakes,
});
} }
Fingerprint LockedFlake::getFingerprint() const Fingerprint LockedFlake::getFingerprint() const

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@ -0,0 +1 @@
"github:NixOS/nixpkgs/23.05?dir=lib"

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@ -0,0 +1,7 @@
builtins.flakeRefToString {
type = "github";
owner = "NixOS";
repo = "nixpkgs";
ref = "23.05";
dir = "lib";
}

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@ -0,0 +1 @@
{ dir = "lib"; owner = "NixOS"; ref = "23.05"; repo = "nixpkgs"; type = "github"; }

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@ -0,0 +1 @@
builtins.parseFlakeRef "github:NixOS/nixpkgs/23.05?dir=lib"