Make the Nix search path declarative

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

View file

@ -48,9 +48,7 @@ Path lookupFileArg(EvalState & state, string s)
{
if (s.size() > 2 && s.at(0) == '<' && s.at(s.size() - 1) == '>') {
Path p = s.substr(1, s.size() - 2);
Path p2 = state.findFile(p);
if (p2 == "") throw Error(format("file `%1%' was not found in the Nix search path (add it using $NIX_PATH or -I)") % p);
return p2;
return state.findFile(p);
} else
return absPath(s);
}

View file

@ -86,6 +86,9 @@ typedef std::map<Path, Path> SrcToStore;
std::ostream & operator << (std::ostream & str, const Value & v);
typedef list<std::pair<string, Path> > SearchPath;
class EvalState
{
public:
@ -111,7 +114,6 @@ private:
#endif
FileEvalCache fileEvalCache;
typedef list<std::pair<string, Path> > SearchPath;
SearchPath searchPath;
public:
@ -137,6 +139,7 @@ public:
/* Look up a file in the search path. */
Path findFile(const string & path);
Path findFile(SearchPath & searchPath, const string & path);
/* Evaluate an expression to normal form, storing the result in
value `v'. */

View file

@ -142,6 +142,7 @@ struct ExprVar : Expr
unsigned int level;
unsigned int displ;
ExprVar(const Symbol & name) : name(name) { };
ExprVar(const Pos & pos, const Symbol & name) : pos(pos), name(name) { };
COMMON_METHODS
Value * maybeThunk(EvalState & state, Env & env);

View file

@ -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);
}

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);

View file

@ -1 +1 @@
"abcc"
"abcca"

View file

@ -8,3 +8,4 @@ assert length (filter (x: x.prefix == "nix") nixPath) == 1;
assert length (filter (x: baseNameOf x.path == "dir4") nixPath) == 1;
import <a.nix> + import <b.nix> + import <c.nix> + import <dir5/c.nix>
+ (let nixPath = [ { path = ./dir1; } { path = ./dir2; } ]; in import <a.nix>)