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Parse string context elements properly

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Prior to this change, we had a bunch of ad-hoc string manipulation code
scattered around. This made it hard to figure out what data model for
string contexts is.

Now, we still store string contexts most of the time as encoded strings
--- I was wary of the performance implications of changing that --- but
whenever we parse them we do so only through the
`NixStringContextElem::parse` method, which handles all cases. This
creates a data type that is very similar to `DerivedPath` but:

 - Represents the funky `=<drvpath>` case as properly distinct from the
   others.

 - Only encodes a single output, no wildcards and no set, for the
   "built" case.

(I would like to deprecate `=<path>`, after which we are in spitting
distance of `DerivedPath` and could maybe get away with fewer types, but
that is another topic for another day.)
This commit is contained in:
John Ericson 2023-01-03 11:44:59 -05:00
parent da64f026dd
commit 5576d5e987
14 changed files with 347 additions and 111 deletions
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51
src/libexpr/primops/context.cc
View file

@ -37,8 +37,15 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx p
auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardOutputDependency");
PathSet context2;
for (auto & p : context)
context2.insert(p.at(0) == '=' ? std::string(p, 1) : p);
for (auto && p : context) {
auto c = NixStringContextElem::parse(*state.store, p);
if (auto * ptr = std::get_if<NixStringContextElem::DrvDeep>(&c)) {
context2.emplace(state.store->printStorePath(ptr->drvPath));
} else {
/* Can reuse original item */
context2.emplace(std::move(p));
}
}
v.mkString(*s, context2);
}
@ -74,34 +81,22 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
};
PathSet context;
state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.getContext");
auto contextInfos = std::map<Path, ContextInfo>();
auto contextInfos = std::map<StorePath, ContextInfo>();
for (const auto & p : context) {
Path drv;
std::string output;
const Path * path = &p;
if (p.at(0) == '=') {
drv = std::string(p, 1);
path = &drv;
} else if (p.at(0) == '!') {
NixStringContextElem ctx = decodeContext(*state.store, p);
drv = state.store->printStorePath(ctx.first);
output = ctx.second;
path = &drv;
}
auto isPath = drv.empty();
auto isAllOutputs = (!drv.empty()) && output.empty();
auto iter = contextInfos.find(*path);
if (iter == contextInfos.end()) {
contextInfos.emplace(*path, ContextInfo{isPath, isAllOutputs, output.empty() ? Strings{} : Strings{std::move(output)}});
} else {
if (isPath)
iter->second.path = true;
else if (isAllOutputs)
iter->second.allOutputs = true;
else
iter->second.outputs.emplace_back(std::move(output));
}
NixStringContextElem ctx = NixStringContextElem::parse(*state.store, p);
std::visit(overloaded {
[&](NixStringContextElem::DrvDeep & d) {
contextInfos[d.drvPath].allOutputs = true;
},
[&](NixStringContextElem::Built & b) {
contextInfos[b.drvPath].outputs.emplace_back(std::move(output));
},
[&](NixStringContextElem::Opaque & o) {
contextInfos[o.path].path = true;
},
}, ctx.raw());
}
auto attrs = state.buildBindings(contextInfos.size());
@ -120,7 +115,7 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
for (const auto & [i, output] : enumerate(info.second.outputs))
(outputsVal.listElems()[i] = state.allocValue())->mkString(output);
}
attrs.alloc(info.first).mkAttrs(infoAttrs);
attrs.alloc(state.store->printStorePath(info.first)).mkAttrs(infoAttrs);
}
v.mkAttrs(attrs);