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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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23
src/libexpr/parser.y
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@ -386,17 +386,10 @@ expr_simple
| PATH { $$ = new ExprPath(absPath($1, data->basePath)); }
| SPATH {
string path($1 + 1, strlen($1) - 2);
Path path2 = data->state.findFile(path);
/* The file wasn't found in the search path. However, we can't
throw an error here, because the expression might never be
evaluated. So return an expression that lazily calls
‘throw’. */
$$ = path2 == ""
? (Expr * ) new ExprApp(
new ExprBuiltin(data->symbols.create("throw")),
new ExprString(data->symbols.create(
(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % path).str())))
: (Expr * ) new ExprPath(path2);
$$ = new ExprApp(CUR_POS,
new ExprApp(new ExprVar(data->symbols.create("__findFile")),
new ExprVar(data->symbols.create("nixPath"))),
new ExprString(data->symbols.create(path)));
}
| URI { $$ = new ExprString(data->symbols.create($1)); }
| '(' expr ')' { $$ = $2; }
@ -636,6 +629,12 @@ void EvalState::addToSearchPath(const string & s, bool warn)
Path EvalState::findFile(const string & path)
{
return findFile(searchPath, path);
}
Path EvalState::findFile(SearchPath & searchPath, const string & path)
{
foreach (SearchPath::iterator, i, searchPath) {
Path res;
@ -650,7 +649,7 @@ Path EvalState::findFile(const string & path)
}
if (pathExists(res)) return canonPath(res);
}
return "";
throw ThrownError(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % path);
}