Build a minimized Nix with MinGW

At this point many features are stripped out, but this works:

- Can run libnix{util,store,expr} unit tests
- Can run some Nix commands

Co-Authored-By volth <volth@volth.com>
Co-Authored-By Brian McKenna <brian@brianmckenna.org>

src/libutil/windows/environment-variables.cc

@@ -0,0 +1,17 @@
+#include "environment-variables.hh"
+
+#include "processenv.h"
+
+namespace nix {
+
+int unsetenv(const char *name)
+{
+    return -SetEnvironmentVariableA(name, nullptr);
+}
+
+int setEnv(const char * name, const char * value)
+{
+    return -SetEnvironmentVariableA(name, value);
+}
+
+}

src/libutil/windows/file-descriptor.cc

@@ -0,0 +1,148 @@
+#include "file-system.hh"
+#include "signals.hh"
+#include "finally.hh"
+#include "serialise.hh"
+#include "windows-error.hh"
+#include "file-path.hh"
+
+#include <fileapi.h>
+#include <error.h>
+#include <namedpipeapi.h>
+#include <namedpipeapi.h>
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+namespace nix {
+
+std::string readFile(HANDLE handle)
+{
+    LARGE_INTEGER li;
+    if (!GetFileSizeEx(handle, &li))
+        throw WinError("%s:%d statting file", __FILE__, __LINE__);
+
+    return drainFD(handle, true, li.QuadPart);
+}
+
+
+void readFull(HANDLE handle, char * buf, size_t count)
+{
+    while (count) {
+        checkInterrupt();
+        DWORD res;
+        if (!ReadFile(handle, (char *) buf, count, &res, NULL))
+            throw WinError("%s:%d reading from file", __FILE__, __LINE__);
+        if (res == 0) throw EndOfFile("unexpected end-of-file");
+        count -= res;
+        buf += res;
+    }
+}
+
+
+void writeFull(HANDLE handle, std::string_view s, bool allowInterrupts)
+{
+    while (!s.empty()) {
+        if (allowInterrupts) checkInterrupt();
+        DWORD res;
+#if _WIN32_WINNT >= 0x0600
+        auto path = handleToPath(handle); // debug; do it before becuase handleToPath changes lasterror
+        if (!WriteFile(handle, s.data(), s.size(), &res, NULL)) {
+            throw WinError("writing to file %1%:%2%", handle, path);
+        }
+#else
+        if (!WriteFile(handle, s.data(), s.size(), &res, NULL)) {
+            throw WinError("writing to file %1%", handle);
+        }
+#endif
+        if (res > 0)
+            s.remove_prefix(res);
+    }
+}
+
+
+std::string readLine(HANDLE handle)
+{
+    std::string s;
+    while (1) {
+        checkInterrupt();
+        char ch;
+        // FIXME: inefficient
+        DWORD rd;
+        if (!ReadFile(handle, &ch, 1, &rd, NULL)) {
+            throw WinError("reading a line");
+        } else if (rd == 0)
+            throw EndOfFile("unexpected EOF reading a line");
+        else {
+            if (ch == '\n') return s;
+            s += ch;
+        }
+    }
+}
+
+
+void drainFD(HANDLE handle, Sink & sink/*, bool block*/)
+{
+    std::vector<unsigned char> buf(64 * 1024);
+    while (1) {
+        checkInterrupt();
+        DWORD rd;
+        if (!ReadFile(handle, buf.data(), buf.size(), &rd, NULL)) {
+            WinError winError("%s:%d reading from handle %p", __FILE__, __LINE__, handle);
+            if (winError.lastError == ERROR_BROKEN_PIPE)
+                break;
+            throw winError;
+        }
+        else if (rd == 0) break;
+        sink({(char *) buf.data(), (size_t) rd});
+    }
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+
+void Pipe::create()
+{
+    SECURITY_ATTRIBUTES saAttr = {0};
+    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
+    saAttr.lpSecurityDescriptor = NULL;
+    saAttr.bInheritHandle = TRUE;
+
+    HANDLE hReadPipe, hWritePipe;
+    if (!CreatePipe(&hReadPipe, &hWritePipe, &saAttr, 0))
+        throw WinError("CreatePipe");
+
+    readSide = hReadPipe;
+    writeSide = hWritePipe;
+}
+
+
+//////////////////////////////////////////////////////////////////////
+
+#if _WIN32_WINNT >= 0x0600
+
+std::wstring handleToFileName(HANDLE handle) {
+    std::vector<wchar_t> buf(0x100);
+    DWORD dw = GetFinalPathNameByHandleW(handle, buf.data(), buf.size(), FILE_NAME_OPENED);
+    if (dw == 0) {
+        if (handle == GetStdHandle(STD_INPUT_HANDLE )) return L"<stdin>";
+        if (handle == GetStdHandle(STD_OUTPUT_HANDLE)) return L"<stdout>";
+        if (handle == GetStdHandle(STD_ERROR_HANDLE )) return L"<stderr>";
+        return (boost::wformat(L"<unnnamed handle %X>") % handle).str();
+    }
+    if (dw > buf.size()) {
+        buf.resize(dw);
+        if (GetFinalPathNameByHandleW(handle, buf.data(), buf.size(), FILE_NAME_OPENED) != dw-1)
+            throw WinError("GetFinalPathNameByHandleW");
+        dw -= 1;
+    }
+    return std::wstring(buf.data(), dw);
+}
+
+
+Path handleToPath(HANDLE handle) {
+    return os_string_to_string(handleToFileName(handle));
+}
+
+#endif
+
+}

src/libutil/windows/file-path.cc

@@ -0,0 +1,52 @@
+#include <algorithm>
+#include <codecvt>
+#include <iostream>
+#include <locale>
+
+#include "file-path.hh"
+#include "file-path-impl.hh"
+#include "util.hh"
+
+namespace nix {
+
+std::string os_string_to_string(PathViewNG::string_view path)
+{
+    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
+    return converter.to_bytes(PathNG::string_type { path });
+}
+
+PathNG::string_type string_to_os_string(std::string_view s)
+{
+    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
+    return converter.from_bytes(std::string { s });
+}
+
+std::optional<PathNG> maybePathNG(PathView path)
+{
+    if (path.length() >= 3 && (('A' <= path[0] && path[0] <= 'Z') || ('a' <= path[0] && path[0] <= 'z')) && path[1] == ':' && WindowsPathTrait<char>::isPathSep(path[2])) {
+        PathNG::string_type sw = string_to_os_string(
+            std::string { "\\\\?\\" } + path);
+        std::replace(sw.begin(), sw.end(), '/', '\\');
+        return sw;
+    }
+    if (path.length() >= 7 && path[0] == '\\' && path[1] == '\\' && (path[2] == '.' || path[2] == '?') && path[3] == '\\' &&
+               ('A' <= path[4] && path[4] <= 'Z') && path[5] == ':' && WindowsPathTrait<char>::isPathSep(path[6])) {
+        PathNG::string_type sw = string_to_os_string(path);
+        std::replace(sw.begin(), sw.end(), '/', '\\');
+        return sw;
+    }
+    return std::optional<PathNG::string_type>();
+}
+
+PathNG pathNG(PathView path)
+{
+    std::optional<PathNG::string_type> sw = maybePathNG(path);
+    if (!sw) {
+        // FIXME why are we not using the regular error handling?
+        std::cerr << "invalid path for WinAPI call ["<<path<<"]"<<std::endl;
+        _exit(111);
+    }
+    return *sw;
+}
+
+}

src/libutil/windows/processes.cc

@@ -0,0 +1,48 @@
+#include "current-process.hh"
+#include "environment-variables.hh"
+#include "signals.hh"
+#include "processes.hh"
+#include "finally.hh"
+#include "serialise.hh"
+
+#include <cerrno>
+#include <cstdlib>
+#include <cstring>
+#include <future>
+#include <iostream>
+#include <sstream>
+#include <thread>
+
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef __APPLE__
+# include <sys/syscall.h>
+#endif
+
+#ifdef __linux__
+# include <sys/prctl.h>
+# include <sys/mman.h>
+#endif
+
+
+namespace nix {
+
+std::string runProgram(Path program, bool searchPath, const Strings & args,
+    const std::optional<std::string> & input, bool isInteractive)
+{
+    throw UnimplementedError("Cannot shell out to git on Windows yet");
+}
+
+// Output = error code + "standard out" output stream
+std::pair<int, std::string> runProgram(RunOptions && options)
+{
+    throw UnimplementedError("Cannot shell out to git on Windows yet");
+}
+
+void runProgram2(const RunOptions & options)
+{
+    throw UnimplementedError("Cannot shell out to git on Windows yet");
+}
+
+}

src/libutil/windows/signals-impl.hh

@@ -0,0 +1,41 @@
+#pragma once
+///@file
+
+#include "types.hh"
+
+namespace nix {
+
+/* User interruption. */
+
+static inline void setInterrupted(bool isInterrupted)
+{
+    /* Do nothing for now */
+}
+
+static inline bool getInterrupted()
+{
+    return false;
+}
+
+inline void setInterruptThrown()
+{
+    /* Do nothing for now */
+}
+
+void inline checkInterrupt()
+{
+    /* Do nothing for now */
+}
+
+/**
+ * Does nothing, unlike Unix counterpart, but allows avoiding C++
+ */
+struct ReceiveInterrupts
+{
+    /**
+     * Explicit destructor avoids dead code warnings.
+     */
+    ~ReceiveInterrupts() {}
+};
+
+}

src/libutil/windows/users.cc

@@ -0,0 +1,50 @@
+#include "util.hh"
+#include "users.hh"
+#include "environment-variables.hh"
+#include "file-system.hh"
+#include "windows-error.hh"
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+namespace nix {
+
+std::string getUserName()
+{
+    // Get the required buffer size
+    DWORD size = 0;
+    if (!GetUserNameA(nullptr, &size)) {
+        auto lastError = GetLastError();
+        if (lastError != ERROR_INSUFFICIENT_BUFFER)
+            throw WinError(lastError, "cannot figure out size of user name");
+    }
+
+    std::string name;
+    // Allocate a buffer of sufficient size
+    //
+    // - 1 because no need for null byte
+    name.resize(size - 1);
+
+    // Retrieve the username
+    if (!GetUserNameA(&name[0], &size))
+        throw WinError("cannot figure out user name");
+
+    return name;
+}
+
+Path getHome()
+{
+    static Path homeDir = []()
+    {
+        Path homeDir = getEnv("USERPROFILE").value_or("C:\\Users\\Default");
+        assert(!homeDir.empty());
+        return canonPath(homeDir);
+    }();
+    return homeDir;
+}
+
+bool isRootUser() {
+    return false;
+}
+
+}

src/libutil/windows/windows-error.cc

@@ -0,0 +1,31 @@
+#include "windows-error.hh"
+
+#include <error.h>
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+namespace nix {
+
+std::string WinError::renderError(DWORD lastError)
+{
+    LPSTR errorText = NULL;
+
+    FormatMessageA( FORMAT_MESSAGE_FROM_SYSTEM // use system message tables to retrieve error text
+                   |FORMAT_MESSAGE_ALLOCATE_BUFFER // allocate buffer on local heap for error text
+                   |FORMAT_MESSAGE_IGNORE_INSERTS,   // Important! will fail otherwise, since we're not  (and CANNOT) pass insertion parameters
+                    NULL,    // unused with FORMAT_MESSAGE_FROM_SYSTEM
+                    lastError,
+                    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                    (LPTSTR)&errorText,  // output
+                    0, // minimum size for output buffer
+                    NULL);   // arguments - see note
+
+    if (NULL != errorText ) {
+        std::string s2 { errorText };
+        LocalFree(errorText);
+        return s2;
+    }
+    return fmt("CODE=%d", lastError);
+}
+
+}

src/libutil/windows/windows-error.hh

@@ -0,0 +1,51 @@
+#pragma once
+///@file
+
+#include <errhandlingapi.h>
+
+#include "error.hh"
+
+namespace nix {
+
+/**
+ * Windows Error type.
+ *
+ * Unless you need to catch a specific error number, don't catch this in
+ * portable code. Catch `SystemError` instead.
+ */
+class WinError : public SystemError
+{
+public:
+    DWORD lastError;
+
+    /**
+     * Construct using the explicitly-provided error number.
+     * `FormatMessageA` will be used to try to add additional
+     * information to the message.
+     */
+    template<typename... Args>
+    WinError(DWORD lastError, const Args & ... args)
+        : SystemError(""), lastError(lastError)
+    {
+        auto hf = HintFmt(args...);
+        err.msg = HintFmt("%1%: %2%", Uncolored(hf.str()), renderError(lastError));
+    }
+
+    /**
+     * Construct using `GetLastError()` and the ambient "last error".
+     *
+     * Be sure to not perform another last-error-modifying operation
+     * before calling this constructor!
+     */
+    template<typename... Args>
+    WinError(const Args & ... args)
+        : WinError(GetLastError(), args ...)
+    {
+    }
+
+private:
+
+    std::string renderError(DWORD lastError);
+};
+
+}