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nix-shell: look up shell.nix when argument is a directory (NixOS#…
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…11057)

* Refactor: rename runEnv -> isNixShell

* Refactor: rename left -> remainingArgs

* nix-build.cc: Refactor: extract baseDir variable

* nix-build.cc: Refactor: extract sourcePath, resolvedPath variables

* nix-shell: Look for shell.nix when directory is specified

* Add legacy setting: nix-shell-always-looks-for-shell-nix

* rl-next: Add note about shell.nix lookups

* tests/functional/shell.nix: Implement runHook for dummy stdenv
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roberth authored Jul 8, 2024
1 parent d885061 commit cfe3ee3
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28 changes: 28 additions & 0 deletions doc/manual/rl-next/nix-shell-looks-for-shell-nix.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
---
synopsis: "`nix-shell <directory>` looks for `shell.nix`"
significance: significant
issues:
- 496
- 2279
- 4529
- 5431
- 11053
prs:
- 11057
---

`nix-shell $x` now looks for `$x/shell.nix` when `$x` resolves to a directory.

Although this might be seen as a breaking change, its primarily interactive usage makes it a minor issue.
This adjustment addresses a commonly reported problem.

This also applies to `nix-shell` shebang scripts. Consider the following example:

```shell
#!/usr/bin/env nix-shell
#!nix-shell -i bash
```

This will now load `shell.nix` from the script's directory, if it exists; `default.nix` otherwise.

The old behavior can be opted into by setting the option [`nix-shell-always-looks-for-shell-nix`](@docroot@/command-ref/conf-file.md#conf-nix-shell-always-looks-for-shell-nix) to `false`.
7 changes: 7 additions & 0 deletions src/libcmd/common-eval-args.cc
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@
#include "command.hh"
#include "tarball.hh"
#include "fetch-to-store.hh"
#include "compatibility-settings.hh"
#include "eval-settings.hh"

namespace nix {

Expand All @@ -33,6 +35,11 @@ EvalSettings evalSettings {

static GlobalConfig::Register rEvalSettings(&evalSettings);

CompatibilitySettings compatibilitySettings {};

static GlobalConfig::Register rCompatibilitySettings(&compatibilitySettings);


MixEvalArgs::MixEvalArgs()
{
addFlag({
Expand Down
6 changes: 6 additions & 0 deletions src/libcmd/common-eval-args.hh
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ namespace nix {
class Store;
class EvalState;
struct EvalSettings;
struct CompatibilitySettings;
class Bindings;
struct SourcePath;

Expand All @@ -21,6 +22,11 @@ struct SourcePath;
*/
extern EvalSettings evalSettings;

/**
* Settings that control behaviors that have changed since Nix 2.3.
*/
extern CompatibilitySettings compatibilitySettings;

struct MixEvalArgs : virtual Args, virtual MixRepair
{
static constexpr auto category = "Common evaluation options";
Expand Down
19 changes: 19 additions & 0 deletions src/libcmd/compatibility-settings.hh
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
#pragma once
#include "config.hh"

namespace nix {
struct CompatibilitySettings : public Config
{

CompatibilitySettings() = default;

Setting<bool> nixShellAlwaysLooksForShellNix{this, true, "nix-shell-always-looks-for-shell-nix", R"(
Before Nix 2.24, [`nix-shell`](@docroot@/command-ref/nix-shell.md) would only look at `shell.nix` if it was in the working directory - when no file was specified.
Since Nix 2.24, `nix-shell` always looks for a `shell.nix`, whether that's in the working directory, or in a directory that was passed as an argument.
You may set this to `false` to revert to the Nix 2.3 behavior.
)"};
};

};
1 change: 1 addition & 0 deletions src/libcmd/meson.build
Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,7 @@ headers = [config_h] + files(
'command-installable-value.hh',
'command.hh',
'common-eval-args.hh',
'compatibility-settings.hh',
'editor-for.hh',
'installable-attr-path.hh',
'installable-derived-path.hh',
Expand Down
4 changes: 2 additions & 2 deletions src/libexpr/eval.cc
Original file line number Diff line number Diff line change
Expand Up @@ -2650,7 +2650,7 @@ void EvalState::printStatistics()
}


SourcePath resolveExprPath(SourcePath path)
SourcePath resolveExprPath(SourcePath path, bool addDefaultNix)
{
unsigned int followCount = 0, maxFollow = 1024;

Expand All @@ -2666,7 +2666,7 @@ SourcePath resolveExprPath(SourcePath path)
}

/* If `path' refers to a directory, append `/default.nix'. */
if (path.resolveSymlinks().lstat().type == SourceAccessor::tDirectory)
if (addDefaultNix && path.resolveSymlinks().lstat().type == SourceAccessor::tDirectory)
return path / "default.nix";

return path;
Expand Down
4 changes: 3 additions & 1 deletion src/libexpr/eval.hh
Original file line number Diff line number Diff line change
Expand Up @@ -850,8 +850,10 @@ std::string showType(const Value & v);

/**
* If `path` refers to a directory, then append "/default.nix".
*
* @param addDefaultNix Whether to append "/default.nix" after resolving symlinks.
*/
SourcePath resolveExprPath(SourcePath path);
SourcePath resolveExprPath(SourcePath path, bool addDefaultNix = true);

/**
* Whether a URI is allowed, assuming restrictEval is enabled
Expand Down
90 changes: 64 additions & 26 deletions src/nix-build/nix-build.cc
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include "legacy.hh"
#include "users.hh"
#include "network-proxy.hh"
#include "compatibility-settings.hh"

using namespace nix;
using namespace std::string_literals;
Expand Down Expand Up @@ -90,24 +91,50 @@ static std::vector<std::string> shellwords(const std::string & s)
return res;
}

/**
* Like `resolveExprPath`, but prefers `shell.nix` instead of `default.nix`,
* and if `path` was a directory, it checks eagerly whether `shell.nix` or
* `default.nix` exist, throwing an error if they don't.
*/
static SourcePath resolveShellExprPath(SourcePath path)
{
auto resolvedOrDir = resolveExprPath(path, false);
if (resolvedOrDir.resolveSymlinks().lstat().type == SourceAccessor::tDirectory) {
if ((resolvedOrDir / "shell.nix").pathExists()) {
if (compatibilitySettings.nixShellAlwaysLooksForShellNix) {
return resolvedOrDir / "shell.nix";
} else {
warn("Skipping '%1%', because the setting '%2%' is disabled. This is a deprecated behavior. Consider enabling '%2%'.",
resolvedOrDir / "shell.nix",
"nix-shell-always-looks-for-shell-nix");
}
}
if ((resolvedOrDir / "default.nix").pathExists()) {
return resolvedOrDir / "default.nix";
}
throw Error("neither '%s' nor '%s' found in '%s'", "shell.nix", "default.nix", resolvedOrDir);
}
return resolvedOrDir;
}

static void main_nix_build(int argc, char * * argv)
{
auto dryRun = false;
auto runEnv = std::regex_search(argv[0], std::regex("nix-shell$"));
auto isNixShell = std::regex_search(argv[0], std::regex("nix-shell$"));
auto pure = false;
auto fromArgs = false;
auto packages = false;
// Same condition as bash uses for interactive shells
auto interactive = isatty(STDIN_FILENO) && isatty(STDERR_FILENO);
Strings attrPaths;
Strings left;
Strings remainingArgs;
BuildMode buildMode = bmNormal;
bool readStdin = false;

std::string envCommand; // interactive shell
Strings envExclude;

auto myName = runEnv ? "nix-shell" : "nix-build";
auto myName = isNixShell ? "nix-shell" : "nix-build";

auto inShebang = false;
std::string script;
Expand All @@ -132,7 +159,7 @@ static void main_nix_build(int argc, char * * argv)
// Heuristic to see if we're invoked as a shebang script, namely,
// if we have at least one argument, it's the name of an
// executable file, and it starts with "#!".
if (runEnv && argc > 1) {
if (isNixShell && argc > 1) {
script = argv[1];
try {
auto lines = tokenizeString<Strings>(readFile(script), "\n");
Expand Down Expand Up @@ -186,9 +213,9 @@ static void main_nix_build(int argc, char * * argv)
dryRun = true;

else if (*arg == "--run-env") // obsolete
runEnv = true;
isNixShell = true;

else if (runEnv && (*arg == "--command" || *arg == "--run")) {
else if (isNixShell && (*arg == "--command" || *arg == "--run")) {
if (*arg == "--run")
interactive = false;
envCommand = getArg(*arg, arg, end) + "\nexit";
Expand All @@ -206,7 +233,7 @@ static void main_nix_build(int argc, char * * argv)
else if (*arg == "--pure") pure = true;
else if (*arg == "--impure") pure = false;

else if (runEnv && (*arg == "--packages" || *arg == "-p"))
else if (isNixShell && (*arg == "--packages" || *arg == "-p"))
packages = true;

else if (inShebang && *arg == "-i") {
Expand Down Expand Up @@ -246,7 +273,7 @@ static void main_nix_build(int argc, char * * argv)
return false;

else
left.push_back(*arg);
remainingArgs.push_back(*arg);

return true;
});
Expand All @@ -266,7 +293,7 @@ static void main_nix_build(int argc, char * * argv)
auto autoArgs = myArgs.getAutoArgs(*state);

auto autoArgsWithInNixShell = autoArgs;
if (runEnv) {
if (isNixShell) {
auto newArgs = state->buildBindings(autoArgsWithInNixShell->size() + 1);
newArgs.alloc("inNixShell").mkBool(true);
for (auto & i : *autoArgs) newArgs.insert(i);
Expand All @@ -276,19 +303,26 @@ static void main_nix_build(int argc, char * * argv)
if (packages) {
std::ostringstream joined;
joined << "{...}@args: with import <nixpkgs> args; (pkgs.runCommandCC or pkgs.runCommand) \"shell\" { buildInputs = [ ";
for (const auto & i : left)
for (const auto & i : remainingArgs)
joined << '(' << i << ") ";
joined << "]; } \"\"";
fromArgs = true;
left = {joined.str()};
} else if (!fromArgs) {
if (left.empty() && runEnv && pathExists("shell.nix"))
left = {"shell.nix"};
if (left.empty())
left = {"default.nix"};
remainingArgs = {joined.str()};
} else if (!fromArgs && remainingArgs.empty()) {
if (isNixShell && !compatibilitySettings.nixShellAlwaysLooksForShellNix && std::filesystem::exists("shell.nix")) {
// If we're in 2.3 compatibility mode, we need to look for shell.nix
// now, because it won't be done later.
remainingArgs = {"shell.nix"};
} else {
remainingArgs = {"."};

// Instead of letting it throw later, we throw here to give a more relevant error message
if (isNixShell && !std::filesystem::exists("shell.nix") && !std::filesystem::exists("default.nix"))
throw Error("no argument specified and no '%s' or '%s' file found in the working directory", "shell.nix", "default.nix");
}
}

if (runEnv)
if (isNixShell)
setEnv("IN_NIX_SHELL", pure ? "pure" : "impure");

PackageInfos drvs;
Expand All @@ -299,7 +333,7 @@ static void main_nix_build(int argc, char * * argv)
if (readStdin)
exprs = {state->parseStdin()};
else
for (auto i : left) {
for (auto i : remainingArgs) {
if (fromArgs)
exprs.push_back(state->parseExprFromString(std::move(i), state->rootPath(".")));
else {
Expand All @@ -310,14 +344,18 @@ static void main_nix_build(int argc, char * * argv)
auto [path, outputNames] = parsePathWithOutputs(absolute);
if (evalStore->isStorePath(path) && hasSuffix(path, ".drv"))
drvs.push_back(PackageInfo(*state, evalStore, absolute));
else
else {
/* If we're in a #! script, interpret filenames
relative to the script. */
exprs.push_back(
state->parseExprFromFile(
resolveExprPath(
lookupFileArg(*state,
inShebang && !packages ? absPath(i, absPath(dirOf(script))) : i))));
auto baseDir = inShebang && !packages ? absPath(i, absPath(dirOf(script))) : i;

auto sourcePath = lookupFileArg(*state,
baseDir);
auto resolvedPath =
isNixShell ? resolveShellExprPath(sourcePath) : resolveExprPath(sourcePath);

exprs.push_back(state->parseExprFromFile(resolvedPath));
}
}
}

Expand All @@ -330,7 +368,7 @@ static void main_nix_build(int argc, char * * argv)

std::function<bool(const Value & v)> takesNixShellAttr;
takesNixShellAttr = [&](const Value & v) {
if (!runEnv) {
if (!isNixShell) {
return false;
}
bool add = false;
Expand Down Expand Up @@ -381,7 +419,7 @@ static void main_nix_build(int argc, char * * argv)
store->buildPaths(paths, buildMode, evalStore);
};

if (runEnv) {
if (isNixShell) {
if (drvs.size() != 1)
throw UsageError("nix-shell requires a single derivation");

Expand Down
53 changes: 53 additions & 0 deletions tests/functional/nix-shell.sh
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,10 @@ output=$(nix-shell --pure "$shellDotNix" -A shellDrv --run \

[ "$output" = " - foo - bar - true" ]

output=$(nix-shell --pure "$shellDotNix" -A shellDrv --option nix-shell-always-looks-for-shell-nix false --run \
'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $TEST_inNixShell"')
[ "$output" = " - foo - bar - true" ]

# Test --keep
output=$(nix-shell --pure --keep SELECTED_IMPURE_VAR "$shellDotNix" -A shellDrv --run \
'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $SELECTED_IMPURE_VAR"')
Expand Down Expand Up @@ -91,6 +95,55 @@ sed -e "s|@ENV_PROG@|$(type -P env)|" shell.shebang.nix > $TEST_ROOT/shell.sheba
chmod a+rx $TEST_ROOT/shell.shebang.nix
$TEST_ROOT/shell.shebang.nix

mkdir $TEST_ROOT/lookup-test $TEST_ROOT/empty

echo "import $shellDotNix" > $TEST_ROOT/lookup-test/shell.nix
cp config.nix $TEST_ROOT/lookup-test/
echo 'abort "do not load default.nix!"' > $TEST_ROOT/lookup-test/default.nix

nix-shell $TEST_ROOT/lookup-test -A shellDrv --run 'echo "it works"' | grepQuiet "it works"
# https://github.com/NixOS/nix/issues/4529
nix-shell -I "testRoot=$TEST_ROOT" '<testRoot/lookup-test>' -A shellDrv --run 'echo "it works"' | grepQuiet "it works"

expectStderr 1 nix-shell $TEST_ROOT/lookup-test -A shellDrv --run 'echo "it works"' --option nix-shell-always-looks-for-shell-nix false \
| grepQuiet -F "do not load default.nix!" # we did, because we chose to enable legacy behavior
expectStderr 1 nix-shell $TEST_ROOT/lookup-test -A shellDrv --run 'echo "it works"' --option nix-shell-always-looks-for-shell-nix false \
| grepQuiet "Skipping .*lookup-test/shell\.nix.*, because the setting .*nix-shell-always-looks-for-shell-nix.* is disabled. This is a deprecated behavior\. Consider enabling .*nix-shell-always-looks-for-shell-nix.*"

(
cd $TEST_ROOT/empty;
expectStderr 1 nix-shell | \
grepQuiet "error.*no argument specified and no .*shell\.nix.* or .*default\.nix.* file found in the working directory"
)

expectStderr 1 nix-shell -I "testRoot=$TEST_ROOT" '<testRoot/empty>' |
grepQuiet "error.*neither .*shell\.nix.* nor .*default\.nix.* found in .*/empty"

cat >$TEST_ROOT/lookup-test/shebangscript <<EOF
#!$(type -P env) nix-shell
#!nix-shell -A shellDrv -i bash
[[ \$VAR_FROM_NIX == bar ]]
echo "script works"
EOF
chmod +x $TEST_ROOT/lookup-test/shebangscript

$TEST_ROOT/lookup-test/shebangscript | grepQuiet "script works"

# https://github.com/NixOS/nix/issues/5431
mkdir $TEST_ROOT/marco{,/polo}
echo 'abort "marco/shell.nix must not be used, but its mere existence used to cause #5431"' > $TEST_ROOT/marco/shell.nix
cat >$TEST_ROOT/marco/polo/default.nix <<EOF
#!$(type -P env) nix-shell
(import $TEST_ROOT/lookup-test/shell.nix {}).polo
EOF
chmod a+x $TEST_ROOT/marco/polo/default.nix
(cd $TEST_ROOT/marco && ./polo/default.nix | grepQuiet "Polo")


#####################
# Flake equivalents #
#####################

# Test 'nix develop'.
nix develop -f "$shellDotNix" shellDrv -c bash -c '[[ -n $stdenv ]]'

Expand Down
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