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Make the Nix search path declarative

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Nix search path lookups like <nixpkgs> are now desugared to ‘findFile
nixPath <nixpkgs>’, where ‘findFile’ is a new primop. Thus you can
override the search path simply by saying

  let
    nixPath = [ { prefix = "nixpkgs"; path = "/my-nixpkgs"; } ];
  in ... <nixpkgs> ...

In conjunction with ‘scopedImport’ (commit
c273c15cb1), the Nix search path can be
propagated across imports, e.g.

  let

    overrides = {
      nixPath = [ ... ] ++ builtins.nixPath;
      import = fn: scopedImport overrides fn;
      scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
      builtins = builtins // overrides;
    };

  in scopedImport overrides ./nixos
This commit is contained in:
Eelco Dolstra 2014-05-26 17:02:22 +02:00
parent 39d72640c2
commit 62a6eeb1f3
7 changed files with 51 additions and 17 deletions
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32
src/libexpr/primops.cc
View file

@ -654,6 +654,37 @@ static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Va
}
/* Find a file in the Nix search path. Used to implement <x> paths,
which are desugared to ‘findFile nixPath "x"’. */
static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Value & v)
{
state.forceList(*args[0], pos);
SearchPath searchPath;
for (unsigned int n = 0; n < args[0]->list.length; ++n) {
Value & v2(*args[0]->list.elems[n]);
state.forceAttrs(v2, pos);
string prefix;
Bindings::iterator i = v2.attrs->find(state.symbols.create("prefix"));
if (i != v2.attrs->end())
prefix = state.forceStringNoCtx(*i->value, pos);
i = v2.attrs->find(state.symbols.create("path"));
if (i == v2.attrs->end())
throw EvalError(format("attribute `path' missing, at %1%") % pos);
PathSet context;
string path = state.coerceToPath(pos, *i->value, context);
searchPath.push_back(std::pair<string, Path>(prefix, path));
}
string path = state.forceStringNoCtx(*args[1], pos);
mkPath(v, state.findFile(searchPath, path).c_str());
}
/*************************************************************
* Creating files
*************************************************************/
@ -1293,6 +1324,7 @@ void EvalState::createBaseEnv()
addPrimOp("baseNameOf", 1, prim_baseNameOf);
addPrimOp("dirOf", 1, prim_dirOf);
addPrimOp("__readFile", 1, prim_readFile);
addPrimOp("__findFile", 2, prim_findFile);
// Creating files
addPrimOp("__toXML", 1, prim_toXML);