lix/src/nix/command.hh
Eelco Dolstra 0abb3ad537 Allow content-addressable paths to have references
This adds a command 'nix make-content-addressable' that rewrites the
specified store paths into content-addressable paths. The advantage of
such paths is that 1) they can be imported without signatures; 2) they
can enable deduplication in cases where derivation changes do not
cause output changes (apart from store path hashes).

For example,

  $ nix make-content-addressable -r nixpkgs.cowsay
  rewrote '/nix/store/g1g31ah55xdia1jdqabv1imf6mcw0nb1-glibc-2.25-49' to '/nix/store/48jfj7bg78a8n4f2nhg269rgw1936vj4-glibc-2.25-49'
  ...
  rewrote '/nix/store/qbi6rzpk0bxjw8lw6azn2mc7ynnn455q-cowsay-3.03+dfsg1-16' to '/nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16'

We can then copy the resulting closure to another store without
signatures:

  $ nix copy --trusted-public-keys '' ---to ~/my-nix /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16

In order to support self-references in content-addressable paths,
these paths are hashed "modulo" self-references, meaning that
self-references are zeroed out during hashing. Somewhat annoyingly,
this means that the NAR hash stored in the Nix database is no longer
necessarily equal to the output of "nix hash-path"; for
content-addressable paths, you need to pass the --modulo flag:

  $ nix path-info --json /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16  | jq -r .[].narHash
  sha256:0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16
  1ggznh07khq0hz6id09pqws3a8q9pn03ya3c03nwck1kwq8rclzs

  $ nix hash-path --type sha256 --base32 /nix/store/iq6g2x4q62xp7y7493bibx0qn5w7xz67-cowsay-3.03+dfsg1-16 --modulo iq6g2x4q62xp7y7493bibx0qn5w7xz67
  0ri611gdilz2c9rsibqhsipbfs9vwcqvs811a52i2bnkhv7w9mgw
2019-10-21 17:47:24 +02:00

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#pragma once
#include "args.hh"
#include "common-eval-args.hh"
namespace nix {
extern std::string programPath;
struct Value;
class Bindings;
class EvalState;
/* A command is an argument parser that can be executed by calling its
run() method. */
struct Command : virtual Args
{
virtual std::string name() = 0;
virtual void prepare() { };
virtual void run() = 0;
struct Example
{
std::string description;
std::string command;
};
typedef std::list<Example> Examples;
virtual Examples examples() { return Examples(); }
void printHelp(const string & programName, std::ostream & out) override;
};
class Store;
/* A command that require a Nix store. */
struct StoreCommand : virtual Command
{
StoreCommand();
void run() override;
ref<Store> getStore();
virtual ref<Store> createStore();
virtual void run(ref<Store>) = 0;
private:
std::shared_ptr<Store> _store;
};
struct Buildable
{
Path drvPath; // may be empty
std::map<std::string, Path> outputs;
};
typedef std::vector<Buildable> Buildables;
struct Installable
{
virtual std::string what() = 0;
virtual Buildables toBuildables()
{
throw Error("argument '%s' cannot be built", what());
}
Buildable toBuildable();
virtual Value * toValue(EvalState & state)
{
throw Error("argument '%s' cannot be evaluated", what());
}
};
struct SourceExprCommand : virtual Args, StoreCommand, MixEvalArgs
{
Path file;
SourceExprCommand();
/* Return a value representing the Nix expression from which we
are installing. This is either the file specified by --file,
or an attribute set constructed from $NIX_PATH, e.g. { nixpkgs
= import ...; bla = import ...; }. */
Value * getSourceExpr(EvalState & state);
ref<EvalState> getEvalState();
private:
std::shared_ptr<EvalState> evalState;
Value * vSourceExpr = 0;
};
enum RealiseMode { Build, NoBuild, DryRun };
/* A command that operates on a list of "installables", which can be
store paths, attribute paths, Nix expressions, etc. */
struct InstallablesCommand : virtual Args, SourceExprCommand
{
std::vector<std::shared_ptr<Installable>> installables;
InstallablesCommand()
{
expectArgs("installables", &_installables);
}
void prepare() override;
virtual bool useDefaultInstallables() { return true; }
private:
std::vector<std::string> _installables;
};
struct InstallableCommand : virtual Args, SourceExprCommand
{
std::shared_ptr<Installable> installable;
InstallableCommand()
{
expectArg("installable", &_installable);
}
void prepare() override;
private:
std::string _installable;
};
/* A command that operates on zero or more store paths. */
struct StorePathsCommand : public InstallablesCommand
{
private:
bool recursive = false;
bool all = false;
protected:
RealiseMode realiseMode = NoBuild;
public:
StorePathsCommand(bool recursive = false);
using StoreCommand::run;
virtual void run(ref<Store> store, Paths storePaths) = 0;
void run(ref<Store> store) override;
bool useDefaultInstallables() override { return !all; }
};
/* A command that operates on exactly one store path. */
struct StorePathCommand : public InstallablesCommand
{
using StoreCommand::run;
virtual void run(ref<Store> store, const Path & storePath) = 0;
void run(ref<Store> store) override;
};
typedef std::map<std::string, ref<Command>> Commands;
/* An argument parser that supports multiple subcommands,
i.e. <command> <subcommand>. */
class MultiCommand : virtual Args
{
public:
Commands commands;
std::shared_ptr<Command> command;
MultiCommand(const Commands & commands);
void printHelp(const string & programName, std::ostream & out) override;
bool processFlag(Strings::iterator & pos, Strings::iterator end) override;
bool processArgs(const Strings & args, bool finish) override;
};
/* A helper class for registering commands globally. */
struct RegisterCommand
{
static Commands * commands;
RegisterCommand(ref<Command> command)
{
if (!commands) commands = new Commands;
commands->emplace(command->name(), command);
}
};
std::shared_ptr<Installable> parseInstallable(
SourceExprCommand & cmd, ref<Store> store, const std::string & installable,
bool useDefaultInstallables);
Buildables build(ref<Store> store, RealiseMode mode,
std::vector<std::shared_ptr<Installable>> installables);
PathSet toStorePaths(ref<Store> store, RealiseMode mode,
std::vector<std::shared_ptr<Installable>> installables);
Path toStorePath(ref<Store> store, RealiseMode mode,
std::shared_ptr<Installable> installable);
PathSet toDerivations(ref<Store> store,
std::vector<std::shared_ptr<Installable>> installables,
bool useDeriver = false);
}