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Add 'nix dev-shell' and 'nix print-dev-env' command

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'nix dev-shell' is intended to replace nix-shell. It supports flakes,
e.g.

  $ nix dev-shell nixpkgs:hello

starts a bash shell providing an environment for building 'hello'.

Like Lorri (and unlike nix-shell), it computes the build environment
by building a modified top-level derivation that writes the
environment after running $stdenv/setup to $out and exits. This
provides some caching, so it's faster than nix-shell in some cases
(especially for packages with lots of dependencies, where the setup
script takes a long time).

There also is a command 'nix print-dev-env' that prints out shell code
for setting up the build environment in an existing shell, e.g.

  $ . <(nix print-dev-env nixpkgs:hello)

https://github.com/tweag/nix/issues/21
This commit is contained in:
Eelco Dolstra 2019-05-02 20:22:14 +02:00
parent 4588a6ff3c
commit 2b8c63f303
1 changed files with 276 additions and 0 deletions
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276
src/nix/shell.cc Normal file
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#include "eval.hh"
#include "command.hh"
#include "common-args.hh"
#include "shared.hh"
#include "store-api.hh"
#include "derivations.hh"
#include "affinity.hh"
#include "progress-bar.hh"
using namespace nix;
struct BuildEnvironment
{
// FIXME: figure out which vars should be exported.
std::map<std::string, std::string> env;
std::map<std::string, std::string> functions;
};
BuildEnvironment readEnvironment(const Path & path)
{
BuildEnvironment res;
auto lines = tokenizeString<Strings>(readFile(path), "\n");
auto getLine =
[&]() {
if (lines.empty())
throw Error("shell environment '%s' ends unexpectedly", path);
auto line = lines.front();
lines.pop_front();
return line;
};
while (!lines.empty()) {
auto line = getLine();
auto eq = line.find('=');
if (eq != std::string::npos) {
std::string name(line, 0, eq);
std::string value(line, eq + 1);
// FIXME: parse arrays
res.env.insert({name, value});
}
else if (hasSuffix(line, " () ")) {
std::string name(line, 0, line.size() - 4);
// FIXME: validate name
auto l = getLine();
if (l != "{ ") throw Error("shell environment '%s' has unexpected line '%s'", path, l);
std::string body;
while ((l = getLine()) != "}") {
body += l;
body += '\n';
}
res.functions.insert({name, body});
}
else throw Error("shell environment '%s' has unexpected line '%s'", path, line);
}
return res;
}
/* Given an existing derivation, return the shell environment as
initialised by stdenv's setup script. We do this by building a
modified derivation with the same dependencies and nearly the same
initial environment variables, that just writes the resulting
environment to a file and exits. */
BuildEnvironment getDerivationEnvironment(ref<Store> store, Derivation drv)
{
auto builder = baseNameOf(drv.builder);
if (builder != "bash")
throw Error("'nix shell' only works on derivations that use 'bash' as their builder");
drv.args = {"-c", "set -e; if [[ -n $stdenv ]]; then source $stdenv/setup; fi; set > $out"};
/* Remove derivation checks. */
drv.env.erase("allowedReferences");
drv.env.erase("allowedRequisites");
drv.env.erase("disallowedReferences");
drv.env.erase("disallowedRequisites");
// FIXME: handle structured attrs
/* Rehash and write the derivation. FIXME: would be nice to use
'buildDerivation', but that's privileged. */
auto drvName = drv.env["name"] + "-env";
for (auto & output : drv.outputs)
drv.env.erase(output.first);
drv.env["out"] = "";
drv.env["outputs"] = "out";
drv.outputs["out"] = DerivationOutput("", "", "");
Hash h = hashDerivationModulo(*store, drv);
Path shellOutPath = store->makeOutputPath("out", h, drvName);
drv.outputs["out"].path = shellOutPath;
drv.env["out"] = shellOutPath;
Path shellDrvPath2 = writeDerivation(store, drv, drvName);
/* Build the derivation. */
store->buildPaths({shellDrvPath2});
assert(store->isValidPath(shellOutPath));
return readEnvironment(shellOutPath);
}
struct Common : InstallableCommand
{
/*
std::set<string> keepVars{
"DISPLAY",
"HOME",
"IN_NIX_SHELL",
"LOGNAME",
"NIX_BUILD_SHELL",
"PAGER",
"PATH",
"TERM",
"TZ",
"USER",
};
*/
std::set<string> ignoreVars{
"BASHOPTS",
"EUID",
"NIX_BUILD_TOP",
"PPID",
"PWD",
"SHELLOPTS",
"SHLVL",
"TEMP",
"TEMPDIR",
"TMP",
"TMPDIR",
"UID",
};
void makeRcScript(const BuildEnvironment & buildEnvironment, std::ostream & out)
{
for (auto & i : buildEnvironment.env) {
// FIXME: shellEscape
// FIXME: figure out what to export
// FIXME: handle arrays
if (!ignoreVars.count(i.first) && !hasPrefix(i.first, "BASH_"))
out << fmt("export %s=%s\n", i.first, i.second);
}
for (auto & i : buildEnvironment.functions) {
out << fmt("%s () {\n%s\n}\n", i.first, i.second);
}
// FIXME: set outputs
out << "export NIX_BUILD_TOP=\"$(mktemp -d --tmpdir nix-shell.XXXXXX)\"\n";
for (auto & i : {"TMP", "TMPDIR", "TEMP", "TEMPDIR"})
out << fmt("export %s=\"$NIX_BUILD_TOP\"\n", i);
}
};
std::pair<AutoCloseFD, Path> createTempFile(const Path & prefix = "nix")
{
Path tmpl(getEnv("TMPDIR", "/tmp") + "/" + prefix + ".XXXXXX");
// Strictly speaking, this is UB, but who cares...
AutoCloseFD fd(mkstemp((char *) tmpl.c_str()));
if (!fd)
throw SysError("creating temporary file '%s'", tmpl);
return {std::move(fd), tmpl};
}
struct CmdDevShell : Common
{
std::string name() override
{
return "dev-shell";
}
std::string description() override
{
return "run a bash shell that provides the build environment of a derivation";
}
Examples examples() override
{
return {
Example{
"To get the build environment of GNU hello:",
"nix dev-shell nixpkgs:hello"
},
Example{
"To get the build environment of the default package of flake in the current directory:",
"nix dev-shell"
},
};
}
void run(ref<Store> store) override
{
auto drvs = toDerivations(store, {installable});
if (drvs.size() != 1)
throw Error("'%s' needs to evaluate to a single derivation, but it evaluated to %d derivations",
installable->what(), drvs.size());
auto & drvPath = *drvs.begin();
auto buildEnvironment = getDerivationEnvironment(store, store->derivationFromPath(drvPath));
auto [rcFileFd, rcFilePath] = createTempFile("nix-shell");
std::ostringstream ss;
makeRcScript(buildEnvironment, ss);
ss << fmt("rm -f '%s'\n", rcFilePath);
writeFull(rcFileFd.get(), ss.str());
stopProgressBar();
auto shell = getEnv("SHELL", "bash");
auto args = Strings{baseNameOf(shell), "--rcfile", rcFilePath};
restoreAffinity();
restoreSignals();
execvp(shell.c_str(), stringsToCharPtrs(args).data());
throw SysError("executing shell '%s'", shell);
}
};
struct CmdPrintDevEnv : Common
{
std::string name() override
{
return "print-dev-env";
}
std::string description() override
{
return "print shell code that can be sourced by bash to reproduce the build environment of a derivation";
}
Examples examples() override
{
return {
Example{
"To apply the build environment of GNU hello to the current shell:",
". <(nix print-dev-env nixpkgs:hello)"
},
};
}
void run(ref<Store> store) override
{
auto drvs = toDerivations(store, {installable});
if (drvs.size() != 1)
throw Error("'%s' needs to evaluate to a single derivation, but it evaluated to %d derivations",
installable->what(), drvs.size());
auto & drvPath = *drvs.begin();
auto buildEnvironment = getDerivationEnvironment(store, store->derivationFromPath(drvPath));
stopProgressBar();
makeRcScript(buildEnvironment, std::cout);
}
};
static RegisterCommand r1(make_ref<CmdPrintDevEnv>());
static RegisterCommand r2(make_ref<CmdDevShell>());