lix/src/nix-instantiate/nix-instantiate.cc
Eelco Dolstra d4dcffd643
Add pure evaluation mode
In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
2018-01-16 19:23:18 +01:00

193 lines
6.1 KiB
C++

#include "globals.hh"
#include "shared.hh"
#include "eval.hh"
#include "eval-inline.hh"
#include "get-drvs.hh"
#include "attr-path.hh"
#include "value-to-xml.hh"
#include "value-to-json.hh"
#include "util.hh"
#include "store-api.hh"
#include "common-eval-args.hh"
#include <map>
#include <iostream>
using namespace nix;
static Path gcRoot;
static int rootNr = 0;
static bool indirectRoot = false;
enum OutputKind { okPlain, okXML, okJSON };
void processExpr(EvalState & state, const Strings & attrPaths,
bool parseOnly, bool strict, Bindings & autoArgs,
bool evalOnly, OutputKind output, bool location, Expr * e)
{
if (parseOnly) {
std::cout << format("%1%\n") % *e;
return;
}
Value vRoot;
state.eval(e, vRoot);
for (auto & i : attrPaths) {
Value & v(*findAlongAttrPath(state, i, autoArgs, vRoot));
state.forceValue(v);
PathSet context;
if (evalOnly) {
Value vRes;
if (autoArgs.empty())
vRes = v;
else
state.autoCallFunction(autoArgs, v, vRes);
if (output == okXML)
printValueAsXML(state, strict, location, vRes, std::cout, context);
else if (output == okJSON)
printValueAsJSON(state, strict, vRes, std::cout, context);
else {
if (strict) state.forceValueDeep(vRes);
std::cout << vRes << std::endl;
}
} else {
DrvInfos drvs;
getDerivations(state, v, "", autoArgs, drvs, false);
for (auto & i : drvs) {
Path drvPath = i.queryDrvPath();
/* What output do we want? */
string outputName = i.queryOutputName();
if (outputName == "")
throw Error(format("derivation '%1%' lacks an 'outputName' attribute ") % drvPath);
if (gcRoot == "")
printGCWarning();
else {
Path rootName = gcRoot;
if (++rootNr > 1) rootName += "-" + std::to_string(rootNr);
auto store2 = state.store.dynamic_pointer_cast<LocalFSStore>();
if (store2)
drvPath = store2->addPermRoot(drvPath, rootName, indirectRoot);
}
std::cout << format("%1%%2%\n") % drvPath % (outputName != "out" ? "!" + outputName : "");
}
}
}
}
int main(int argc, char * * argv)
{
return handleExceptions(argv[0], [&]() {
initNix();
initGC();
Strings files;
bool readStdin = false;
bool fromArgs = false;
bool findFile = false;
bool evalOnly = false;
bool parseOnly = false;
OutputKind outputKind = okPlain;
bool xmlOutputSourceLocation = true;
bool strict = false;
Strings attrPaths;
bool wantsReadWrite = false;
RepairFlag repair = NoRepair;
struct MyArgs : LegacyArgs, MixEvalArgs
{
using LegacyArgs::LegacyArgs;
};
MyArgs myArgs(baseNameOf(argv[0]), [&](Strings::iterator & arg, const Strings::iterator & end) {
if (*arg == "--help")
showManPage("nix-instantiate");
else if (*arg == "--version")
printVersion("nix-instantiate");
else if (*arg == "-")
readStdin = true;
else if (*arg == "--expr" || *arg == "-E")
fromArgs = true;
else if (*arg == "--eval" || *arg == "--eval-only")
evalOnly = true;
else if (*arg == "--read-write-mode")
wantsReadWrite = true;
else if (*arg == "--parse" || *arg == "--parse-only")
parseOnly = evalOnly = true;
else if (*arg == "--find-file")
findFile = true;
else if (*arg == "--attr" || *arg == "-A")
attrPaths.push_back(getArg(*arg, arg, end));
else if (*arg == "--add-root")
gcRoot = getArg(*arg, arg, end);
else if (*arg == "--indirect")
indirectRoot = true;
else if (*arg == "--xml")
outputKind = okXML;
else if (*arg == "--json")
outputKind = okJSON;
else if (*arg == "--no-location")
xmlOutputSourceLocation = false;
else if (*arg == "--strict")
strict = true;
else if (*arg == "--repair")
repair = Repair;
else if (*arg == "--dry-run")
settings.readOnlyMode = true;
else if (*arg != "" && arg->at(0) == '-')
return false;
else
files.push_back(*arg);
return true;
});
myArgs.parseCmdline(argvToStrings(argc, argv));
if (evalOnly && !wantsReadWrite)
settings.readOnlyMode = true;
auto store = openStore();
EvalState state(myArgs.searchPath, store);
state.repair = repair;
Bindings & autoArgs = *myArgs.getAutoArgs(state);
if (attrPaths.empty()) attrPaths = {""};
if (findFile) {
for (auto & i : files) {
Path p = state.findFile(i);
if (p == "") throw Error(format("unable to find '%1%'") % i);
std::cout << p << std::endl;
}
return;
}
if (readStdin) {
Expr * e = state.parseStdin();
processExpr(state, attrPaths, parseOnly, strict, autoArgs,
evalOnly, outputKind, xmlOutputSourceLocation, e);
} else if (files.empty() && !fromArgs)
files.push_back("./default.nix");
for (auto & i : files) {
Expr * e = fromArgs
? state.parseExprFromString(i, absPath("."))
: state.parseExprFromFile(resolveExprPath(state.checkSourcePath(lookupFileArg(state, i))));
processExpr(state, attrPaths, parseOnly, strict, autoArgs,
evalOnly, outputKind, xmlOutputSourceLocation, e);
}
state.printStats();
});
}