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Catch SystemError in portable code #15015

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Merged
Ericson2314 merged 1 commit into from
Jan 20, 2026
Merged

Catch SystemError in portable code #15015

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2 changes: 1 addition & 1 deletion src/libfetchers/git-utils.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1425,7 +1425,7 @@ std::vector<std::tuple<GitRepoImpl::Submodule, Hash>> GitRepoImpl::getSubmodules
auto [fdTemp, pathTemp] = createTempFile("nix-git-submodules");
try {
writeFull(fdTemp.get(), configS);
} catch (SysError & e) {
} catch (SystemError & e) {
e.addTrace({}, "while writing .gitmodules file to temporary file");
throw;
}
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4 changes: 2 additions & 2 deletions src/libmain/plugin.cc
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Expand Up @@ -83,8 +83,8 @@ void initPlugins()
checkInterrupt();
pluginFiles.emplace_back(ent.path());
}
} catch (SysError & e) {
if (e.errNo != ENOTDIR)
} catch (SystemError & e) {
if (!e.is(std::errc::not_a_directory))
throw;
pluginFiles.emplace_back(pluginFile);
}
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4 changes: 2 additions & 2 deletions src/libstore/build/derivation-building-goal.cc
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Expand Up @@ -1028,8 +1028,8 @@ HookReply DerivationBuildingGoal::tryBuildHook(const DerivationOptions<StorePath
else if (reply != "accept")
throw Error("bad hook reply '%s'", reply);

} catch (SysError & e) {
if (e.errNo == EPIPE) {
} catch (SystemError & e) {
if (e.is(std::errc::broken_pipe)) {
printError("build hook died unexpectedly: %s", chomp(drainFD(worker.hook->fromHook.readSide.get())));
worker.hook = 0;
return rpDecline;
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12 changes: 6 additions & 6 deletions src/libstore/builtins/buildenv.cc
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Expand Up @@ -33,8 +33,8 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,

try {
srcFiles = DirectoryIterator{srcDir};
} catch (SysError & e) {
if (e.errNo == ENOTDIR) {
} catch (SystemError & e) {
if (e.is(std::errc::not_a_directory)) {
warn("not including '%s' in the user environment because it's not a directory", srcDir);
return;
}
Expand All @@ -54,8 +54,8 @@ static void createLinks(State & state, const Path & srcDir, const Path & dstDir,
try {
if (stat(srcFile.c_str(), &srcSt) == -1)
throw SysError("getting status of '%1%'", srcFile);
} catch (SysError & e) {
if (e.errNo == ENOENT || e.errNo == ENOTDIR) {
} catch (SystemError & e) {
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@edolstra edolstra Jan 19, 2026

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Does this work? Above it's throwing a SysError with an errno, but where does the errno get converted to an std::errc that can be caught here?

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@xokdvium xokdvium Jan 19, 2026 •
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We now store a std::error_code (system_category) and it's comparable to a std::errc even on windows since fd0bcd9. In unix-like system_category is the same as generic_category, which is just the errno. On windows the comparison goes through the first overload of equivalent virtual function https://en.cppreference.com/w/cpp/error/error_category/equivalent.html, which implements a mapping from windows errors to POSIX ones (std::error_condition is implicitly constructible from std::errc: https://en.cppreference.com/w/cpp/error/error_condition/error_condition.html that uses the generic_category: https://en.cppreference.com/w/cpp/error/errc/make_error_condition.html)

if (e.is(std::errc::no_such_file_or_directory) || e.is(std::errc::not_a_directory)) {
warn("skipping dangling symlink '%s'", dstFile);
continue;
}
Expand Down Expand Up @@ -141,8 +141,8 @@ void buildProfile(const Path & out, Packages && pkgs)
readFile(pkgDir + "/nix-support/propagated-user-env-packages"), " \n"))
if (!done.count(p))
postponed.insert(p);
} catch (SysError & e) {
if (e.errNo != ENOENT && e.errNo != ENOTDIR)
} catch (SystemError & e) {
if (!e.is(std::errc::no_such_file_or_directory) && !e.is(std::errc::not_a_directory))
throw;
}
};
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17 changes: 9 additions & 8 deletions src/libstore/gc.cc
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Expand Up @@ -115,10 +115,10 @@ void LocalStore::addTempRoot(const StorePath & path)
*fdRootsSocket = createUnixDomainSocket();
try {
nix::connect(toSocket(fdRootsSocket->get()), socketPath);
} catch (SysError & e) {
} catch (SystemError & e) {
/* The garbage collector may have exited or not
created the socket yet, so we need to restart. */
if (e.errNo == ECONNREFUSED || e.errNo == ENOENT) {
if (e.is(std::errc::connection_refused) || e.is(std::errc::no_such_file_or_directory)) {
debug("GC socket connection refused: %s", e.msg());
fdRootsSocket->close();
std::this_thread::sleep_for(std::chrono::milliseconds(100));
Expand All @@ -135,10 +135,10 @@ void LocalStore::addTempRoot(const StorePath & path)
readFull(fdRootsSocket->get(), &c, 1);
assert(c == '1');
debug("got ack for GC root '%s'", printStorePath(path));
} catch (SysError & e) {
} catch (SystemError & e) {
/* The garbage collector may have exited, so we need to
restart. */
if (e.errNo == EPIPE || e.errNo == ECONNRESET) {
if (e.is(std::errc::broken_pipe) || e.is(std::errc::connection_reset)) {
debug("GC socket disconnected");
fdRootsSocket->close();
goto restart;
Expand Down Expand Up @@ -280,9 +280,10 @@ void LocalStore::findRoots(const Path & path, std::filesystem::file_type type, R
throw;
}

catch (SysError & e) {
catch (SystemError & e) {
/* We only ignore permanent failures. */
if (e.errNo == EACCES || e.errNo == ENOENT || e.errNo == ENOTDIR)
if (e.is(std::errc::permission_denied) || e.is(std::errc::no_such_file_or_directory)
|| e.is(std::errc::not_a_directory))
printInfo("cannot read potential root '%1%'", path);
else
throw;
Expand Down Expand Up @@ -347,8 +348,8 @@ static void readFileRoots(const std::filesystem::path & path, UncheckedRoots & r
{
try {
roots[readFile(path)].emplace(path.string());
} catch (SysError & e) {
if (e.errNo != ENOENT && e.errNo != EACCES)
} catch (SystemError & e) {
if (!e.is(std::errc::no_such_file_or_directory) && !e.is(std::errc::permission_denied))
throw;
}
}
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4 changes: 2 additions & 2 deletions src/libstore/local-store.cc
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Expand Up @@ -234,8 +234,8 @@ LocalStore::LocalStore(ref<const Config> config)
Path globalLockPath = dbDir + "/big-lock";
try {
globalLock = openLockFile(globalLockPath.c_str(), true);
} catch (SysError & e) {
if (e.errNo == EACCES || e.errNo == EPERM) {
} catch (SystemError & e) {
if (e.is(std::errc::permission_denied) || e.is(std::errc::operation_not_permitted)) {
e.addTrace(
{},
"This command may have been run as non-root in a single-user Nix installation,\n"
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4 changes: 2 additions & 2 deletions src/libstore/remote-store.cc
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Expand Up @@ -377,10 +377,10 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
}
}
conn.processStderr();
} catch (SysError & e) {
} catch (SystemError & e) {
/* Daemon closed while we were sending the path. Probably OOM
or I/O error. */
if (e.errNo == EPIPE)
if (e.is(std::errc::broken_pipe))
try {
conn.processStderr();
} catch (EndOfFile & e) {
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4 changes: 2 additions & 2 deletions src/libutil/file-system.cc
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Expand Up @@ -236,9 +236,9 @@ bool pathAccessible(const std::filesystem::path & path)
{
try {
return pathExists(path.string());
} catch (SysError & e) {
} catch (SystemError & e) {
// swallow EPERM
if (e.errNo == EPERM)
if (e.is(std::errc::operation_not_permitted))
return false;
throw;
}
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4 changes: 2 additions & 2 deletions src/nix/build-remote/build-remote.cc
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Expand Up @@ -264,8 +264,8 @@ static int main_build_remote(int argc, char ** argv)
};
try {
setUpdateLock(storeUri);
} catch (SysError & e) {
if (e.errNo != ENAMETOOLONG)
} catch (SystemError & e) {
if (!e.is(std::errc::filename_too_long))
throw;
// Try again hashing the store URL so we have a shorter path
auto h = hashString(HashAlgorithm::MD5, storeUri);
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