andrewrk/microsoft_craziness.h

## microsoft_craziness.h
//
// Author:   Jonathan Blow
// Version:  1
// Date:     31 August, 2018
//
// This code is released under the MIT license, which you can find at
//
//          https://opensource.org/licenses/MIT
//
//
//
// See the comments for how to use this library just below the includes.
//


#include <windows.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <stdio.h>
#include <sys/stat.h>

#include <stdint.h>
#include <io.h>         // For _get_osfhandle


//
// HOW TO USE THIS CODE
//
// The purpose of this file is to find the folders that contain libraries
// you may need to link against, on Windows, if you are linking with any
// compiled C or C++ code. This will be necessary for many non-C++ programming
// language environments that want to provide compatibility.
//
// We find the place where the Visual Studio libraries live (for example,
// libvcruntime.lib), where the linker and compiler executables live
// (for example, link.exe), and where the Windows SDK libraries reside
// (kernel32.lib, libucrt.lib).
//
// We all wish you didn't have to worry about so many weird dependencies,
// but we don't really have a choice about this, sadly.
//
// I don't claim that this is the absolute best way to solve this problem,
// and so far we punt on things (if you have multiple versions of Visual Studio
// installed, we return the first one, rather than the newest). But it
// will solve the basic problem for you as simply as I know how to do it,
// and because there isn't too much code here, it's easy to modify and expand.
//
//
// Here is the API you need to know about:
//

struct Find_Result {
    int windows_sdk_version;   // Zero if no Windows SDK found.

    wchar_t *windows_sdk_root              = NULL;
    wchar_t *windows_sdk_um_library_path   = NULL;
    wchar_t *windows_sdk_ucrt_library_path = NULL;

    wchar_t *vs_exe_path = NULL;
    wchar_t *vs_library_path = NULL;
};

Find_Result find_visual_studio_and_windows_sdk();

void free_resources(Find_Result *result) {
    free(result->windows_sdk_root);
    free(result->windows_sdk_um_library_path);
    free(result->windows_sdk_ucrt_library_path);
    free(result->vs_exe_path);
    free(result->vs_library_path);
}

//
// Call find_visual_studio_and_windows_sdk, look at the resulting
// paths, then call free_resources on the result.
//
// Everything else in this file is implementation details that you
// don't need to care about.
//

//
// This file was about 400 lines before we started adding these comments.
// You might think that's way too much code to do something as simple
// as finding a few library and executable paths. I agree. However,
// Microsoft's own solution to this problem, called "vswhere", is a
// mere EIGHT THOUSAND LINE PROGRAM, spread across 70 files,
// that they posted to github *unironically*.
//
// I am not making this up: https://github.com/Microsoft/vswhere
//
// Several people have therefore found the need to solve this problem
// themselves. We referred to some of these other solutions when
// figuring out what to do, most prominently ziglang's version,
// by Ryan Saunderson.
//
// I hate this kind of code. The fact that we have to do this at all
// is stupid, and the actual maneuvers we need to go through
// are just painful. If programming were like this all the time,
// I would quit.
//
// Because this is such an absurd waste of time, I felt it would be
// useful to package the code in an easily-reusable way, in the
// style of the stb libraries. We haven't gone as all-out as some
// of the stb libraries do (which compile in C with no includes, often).
// For this version you need C++ and the headers at the top of the file.
//
// We return the strings as Windows wide character strings. Aesthetically
// I don't like that (I think most sane programs are UTF-8 internally),
// but apparently, not all valid Windows file paths can even be converted
// correctly to UTF-8. So have fun with that. It felt safest and simplest
// to stay with wchar_t since all of this code is fully ensconced in
// Windows crazy-land.
//
// One other shortcut I took is that this is hardcoded to return the
// folders for x64 libraries. If you want x86 or arm, you can make
// slight edits to the code below, or, if enough people want this,
// I can work it in here.
//

// Defer macro/thing.

#define CONCAT_INTERNAL(x,y) x##y
#define CONCAT(x,y) CONCAT_INTERNAL(x,y)

template<typename T>
struct ExitScope {
    T lambda;
    ExitScope(T lambda):lambda(lambda){}
    ~ExitScope(){lambda();}
    ExitScope(const ExitScope&);
  private:
    ExitScope& operator =(const ExitScope&);
};

class ExitScopeHelp {
  public:
    template<typename T>
        ExitScope<T> operator+(T t){ return t;}
};

#define defer const auto& CONCAT(defer__, __LINE__) = ExitScopeHelp() + [&]()


// COM objects for the ridiculous Microsoft craziness.

struct DECLSPEC_UUID("B41463C3-8866-43B5-BC33-2B0676F7F42E") DECLSPEC_NOVTABLE ISetupInstance : public IUnknown
{
    STDMETHOD(GetInstanceId)(_Out_ BSTR* pbstrInstanceId) = 0;
    STDMETHOD(GetInstallDate)(_Out_ LPFILETIME pInstallDate) = 0;
    STDMETHOD(GetInstallationName)(_Out_ BSTR* pbstrInstallationName) = 0;
    STDMETHOD(GetInstallationPath)(_Out_ BSTR* pbstrInstallationPath) = 0;
    STDMETHOD(GetInstallationVersion)(_Out_ BSTR* pbstrInstallationVersion) = 0;
    STDMETHOD(GetDisplayName)(_In_ LCID lcid, _Out_ BSTR* pbstrDisplayName) = 0;
    STDMETHOD(GetDescription)(_In_ LCID lcid, _Out_ BSTR* pbstrDescription) = 0;
    STDMETHOD(ResolvePath)(_In_opt_z_ LPCOLESTR pwszRelativePath, _Out_ BSTR* pbstrAbsolutePath) = 0;
};

struct DECLSPEC_UUID("6380BCFF-41D3-4B2E-8B2E-BF8A6810C848") DECLSPEC_NOVTABLE IEnumSetupInstances : public IUnknown
{
    STDMETHOD(Next)(_In_ ULONG celt, _Out_writes_to_(celt, *pceltFetched) ISetupInstance** rgelt, _Out_opt_ _Deref_out_range_(0, celt) ULONG* pceltFetched) = 0;
    STDMETHOD(Skip)(_In_ ULONG celt) = 0;
    STDMETHOD(Reset)(void) = 0;
    STDMETHOD(Clone)(_Deref_out_opt_ IEnumSetupInstances** ppenum) = 0;
};

struct DECLSPEC_UUID("42843719-DB4C-46C2-8E7C-64F1816EFD5B") DECLSPEC_NOVTABLE ISetupConfiguration : public IUnknown
{
    STDMETHOD(EnumInstances)(_Out_ IEnumSetupInstances** ppEnumInstances) = 0;
    STDMETHOD(GetInstanceForCurrentProcess)(_Out_ ISetupInstance** ppInstance) = 0;
    STDMETHOD(GetInstanceForPath)(_In_z_ LPCWSTR wzPath, _Out_ ISetupInstance** ppInstance) = 0;
};


// The beginning of the actual code that does things.

struct Version_Data {
    int32_t best_version[4];  // For Windows 8 versions, only two of these numbers are used.
    wchar_t *best_name;
};

bool os_file_exists(wchar_t *name) {
    // @Robustness: What flags do we really want to check here?

    auto attrib = GetFileAttributesW(name);
    if (attrib == INVALID_FILE_ATTRIBUTES) return false;
    if (attrib & FILE_ATTRIBUTE_DIRECTORY) return false;

    return true;
}

wchar_t *concat(wchar_t *a, wchar_t *b, wchar_t *c = nullptr, wchar_t *d = nullptr) {
    // Concatenate up to 4 wide strings together. Allocated with malloc.
    // If you don't like that, use a programming language that actually
    // helps you with using custom allocators. Or just edit the code.

    auto len_a = wcslen(a);
    auto len_b = wcslen(b);

    auto len_c = 0;
    if (c) len_c = wcslen(c);

    auto len_d = 0;
    if (d) len_d = wcslen(d);

    wchar_t *result = (wchar_t *)malloc((len_a + len_b + len_c + len_d + 1) * 2);
    memcpy(result, a, len_a*2);
    memcpy(result + len_a, b, len_b*2);

    if (c) memcpy(result + len_a + len_b, c, len_c * 2);
    if (d) memcpy(result + len_a + len_b + len_c, d, len_d * 2);

    result[len_a + len_b + len_c + len_d] = 0;

    return result;
}

typedef void (*Visit_Proc_W)(wchar_t *short_name, wchar_t *full_name, Version_Data *data);
bool visit_files_w(wchar_t *dir_name, Version_Data *data, Visit_Proc_W proc) {

    // Visit everything in one folder (non-recursively). If it's a directory
    // that doesn't start with ".", call the visit proc on it. The visit proc
    // will see if the filename conforms to the expected versioning pattern.

    auto wildcard_name = concat(dir_name, L"\\*");
    defer { free(wildcard_name); };

    WIN32_FIND_DATAW find_data;
    auto handle = FindFirstFileW(wildcard_name, &find_data);
    if (handle == INVALID_HANDLE_VALUE) return false;

    while (true) {
        if ((find_data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) && (find_data.cFileName[0] != '.')) {
            auto full_name = concat(dir_name, L"\\", find_data.cFileName);
            defer { free(full_name); };

            proc(find_data.cFileName, full_name, data);
        }

        auto success = FindNextFileW(handle, &find_data);
        if (!success) break;
    }

    FindClose(handle);

    return true;
}


wchar_t *find_windows_kit_root(HKEY key, wchar_t *version) {
    // Given a key to an already opened registry entry,
    // get the value stored under the 'version' subkey.
    // If that's not the right terminology, hey, I never do registry stuff.

    DWORD required_length;
    auto rc = RegQueryValueExW(key, version, NULL, NULL, NULL, &required_length);
    if (rc != 0)  return NULL;

    DWORD length = required_length + 2;  // The +2 is for the maybe optional zero later on. Probably we are over-allocating.
    wchar_t *value = (wchar_t *)malloc(length);
    if (!value) return NULL;

    rc = RegQueryValueExW(key, version, NULL, NULL, (LPBYTE)value, &length);  // We know that version is zero-terminated...
    if (rc != 0)  return NULL;

    // The documentation says that if the string for some reason was not stored
    // with zero-termination, we need to manually terminate it. Sigh!!

    if (value[length]) {
        value[length+1] = 0;
    }

    return value;
}

void win10_best(wchar_t *short_name, wchar_t *full_name, Version_Data *data) {
    // Find the Windows 10 subdirectory with the highest version number.

    int i0, i1, i2, i3;
    auto success = swscanf_s(short_name, L"%d.%d.%d.%d", &i0, &i1, &i2, &i3);
    if (success < 4) return;

    if (i0 < data->best_version[0]) return;
    else if (i0 == data->best_version[0]) {
        if (i1 < data->best_version[1]) return;
        else if (i1 == data->best_version[1]) {
            if (i2 < data->best_version[2]) return;
            else if (i2 == data->best_version[2]) {
                if (i3 < data->best_version[3]) return;
            }
        }
    }

    // we have to copy_string and free here because visit_files free's the full_name string
    // after we execute this function, so Win*_Data would contain an invalid pointer.
    if (data->best_name) free(data->best_name);
    data->best_name = _wcsdup(full_name);

    if (data->best_name) {
        data->best_version[0] = i0;
        data->best_version[1] = i1;
        data->best_version[2] = i2;
        data->best_version[3] = i3;
    }
}

void win8_best(wchar_t *short_name, wchar_t *full_name, Version_Data *data) {
    // Find the Windows 8 subdirectory with the highest version number.

    int i0, i1;
    auto success = swscanf_s(short_name, L"winv%d.%d", &i0, &i1);
    if (success < 2) return;

    if (i0 < data->best_version[0]) return;
    else if (i0 == data->best_version[0]) {
        if (i1 < data->best_version[1]) return;
    }

    // we have to copy_string and free here because visit_files free's the full_name string
    // after we execute this function, so Win*_Data would contain an invalid pointer.
    if (data->best_name) free(data->best_name);
    data->best_name = _wcsdup(full_name);

    if (data->best_name) {
        data->best_version[0] = i0;
        data->best_version[1] = i1;
    }
}

void find_windows_kit_root(Find_Result *result) {
    // Information about the Windows 10 and Windows 8 development kits
    // is stored in the same place in the registry. We open a key
    // to that place, first checking preferntially for a Windows 10 kit,
    // then, if that's not found, a Windows 8 kit.

    HKEY main_key;

    auto rc = RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\Windows Kits\\Installed Roots",
                            0, KEY_QUERY_VALUE | KEY_WOW64_32KEY | KEY_ENUMERATE_SUB_KEYS, &main_key);
    if (rc != S_OK) return;
    defer { RegCloseKey(main_key); };

    // Look for a Windows 10 entry.
    auto windows10_root = find_windows_kit_root(main_key, L"KitsRoot10");

    if (windows10_root) {
        defer { free(windows10_root); };
        Version_Data data = {0};
        auto windows10_lib = concat(windows10_root, L"Lib");
        defer { free(windows10_lib); };

        visit_files_w(windows10_lib, &data, win10_best);
        if (data.best_name) {
            result->windows_sdk_version = 10;
            result->windows_sdk_root = data.best_name;
            return;
        }
    }

    // Look for a Windows 8 entry.
    auto windows8_root = find_windows_kit_root(main_key, L"KitsRoot81");

    if (windows8_root) {
        defer { free(windows8_root); };

        auto windows8_lib = concat(windows8_root, L"Lib");
        defer { free(windows8_lib); };

        Version_Data data = {0};
        visit_files_w(windows8_lib, &data, win8_best);
        if (data.best_name) {
            result->windows_sdk_version = 8;
            result->windows_sdk_root = data.best_name;
            return;
        }
    }

    // If we get here, we failed to find anything.
}


void find_visual_studio_by_fighting_through_microsoft_craziness(Find_Result *result) {
    // The name of this procedure is kind of cryptic. Its purpose is
    // to fight through Microsoft craziness. The things that the fine
    // Visual Studio team want you to do, JUST TO FIND A SINGLE FOLDER
    // THAT EVERYONE NEEDS TO FIND, are ridiculous garbage.

    // For earlier versions of Visual Studio, you'd find this information in the registry,
    // similarly to the Windows Kits above. But no, now it's the future, so to ask the
    // question "Where is the Visual Studio folder?" you have to do a bunch of COM object
    // instantiation, enumeration, and querying. (For extra bonus points, try doing this in
    // a new, underdeveloped programming language where you don't have COM routines up
    // and running yet. So fun.)
    //
    // If all this COM object instantiation, enumeration, and querying doesn't give us
    // a useful result, we drop back to the registry-checking method.

    auto rc = CoInitialize(NULL);
    // "Subsequent valid calls return false." So ignore false.
    // if rc != S_OK  return false;

    GUID my_uid                   = {0x42843719, 0xDB4C, 0x46C2, {0x8E, 0x7C, 0x64, 0xF1, 0x81, 0x6E, 0xFD, 0x5B}};
    GUID CLSID_SetupConfiguration = {0x177F0C4A, 0x1CD3, 0x4DE7, {0xA3, 0x2C, 0x71, 0xDB, 0xBB, 0x9F, 0xA3, 0x6D}};

    ISetupConfiguration *config = NULL;
    auto hr = CoCreateInstance(CLSID_SetupConfiguration, NULL, CLSCTX_INPROC_SERVER, my_uid, (void **)&config);
    if (hr != 0)  return;
    defer { config->Release(); };

    IEnumSetupInstances *instances = NULL;
    hr = config->EnumInstances(&instances);
    if (hr != 0)     return;
    if (!instances)  return;
    defer { instances->Release(); };

    while (1) {
        ULONG found = 0;
        ISetupInstance *instance = NULL;
        auto hr = instances->Next(1, &instance, &found);
        if (hr != S_OK) break;

        defer { instance->Release(); };

        BSTR bstr_inst_path;
        hr = instance->GetInstallationPath(&bstr_inst_path);
        if (hr != S_OK)  continue;
        defer { SysFreeString(bstr_inst_path); };

        auto tools_filename = concat(bstr_inst_path, L"\\VC\\Auxiliary\\Build\\Microsoft.VCToolsVersion.default.txt");
        defer { free(tools_filename); };

        FILE *f = nullptr;
        auto open_result = _wfopen_s(&f, tools_filename, L"rt");
        if (open_result != 0) continue;
        if (!f) continue;
        defer { fclose(f); };

        LARGE_INTEGER tools_file_size;
        auto file_handle = (HANDLE)_get_osfhandle(_fileno(f));
        BOOL success = GetFileSizeEx(file_handle, &tools_file_size);
        if (!success) continue;

        auto version_bytes = (tools_file_size.QuadPart + 1) * 2;  // Warning: This multiplication by 2 presumes there is no variable-length encoding in the wchars (wacky characters in the file could betray this expectation).
        wchar_t *version = (wchar_t *)malloc(version_bytes);
        defer { free(version); };

        auto read_result = fgetws(version, version_bytes, f);
        if (!read_result) continue;

        auto version_tail = wcschr(version, '\n');
        if (version_tail)  *version_tail = 0;  // Stomp the data, because nobody cares about it.

        auto library_path = concat(bstr_inst_path, L"\\VC\\Tools\\MSVC\\", version, L"\\lib\\x64");
        auto library_file = concat(library_path, L"\\vcruntime.lib");  // @Speed: Could have library_path point to this string, with a smaller count, to save on memory flailing!

        if (os_file_exists(library_file)) {
            auto link_exe_path = concat(bstr_inst_path, L"\\VC\\Tools\\MSVC\\", version, L"\\bin\\Hostx64\\x64");
            result->vs_exe_path     = link_exe_path;
            result->vs_library_path = library_path;
            return;
        }

        /*
           Ryan Saunderson said:
           "Clang uses the 'SetupInstance->GetInstallationVersion' / ISetupHelper->ParseVersion to find the newest version
           and then reads the tools file to define the tools path - which is definitely better than what i did."

           So... @Incomplete: Should probably pick the newest version...
        */
    }

    // If we get here, we didn't find Visual Studio 2017. Try earlier versions.

    HKEY vs7_key;
    rc = RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\VisualStudio\\SxS\\VS7", 0, KEY_QUERY_VALUE | KEY_WOW64_32KEY, &vs7_key);

    if (rc != S_OK)  return;
    defer { RegCloseKey(vs7_key); };

    // Hardcoded search for 4 prior Visual Studio versions. Is there something better to do here?
    wchar_t *versions[] = { L"14.0", L"12.0", L"11.0", L"10.0" };
    const int NUM_VERSIONS = sizeof(versions) / sizeof(versions[0]);

    for (int i = 0; i < NUM_VERSIONS; i++) {
        auto v = versions[i];

        DWORD dw_type;
        DWORD cb_data;

        auto rc = RegQueryValueExW(vs7_key, v, NULL, &dw_type, NULL, &cb_data);
        if ((rc == ERROR_FILE_NOT_FOUND) || (dw_type != REG_SZ)) {
            continue;
        }

        auto buffer = (wchar_t *)malloc(cb_data);
        if (!buffer)  return;
        defer { free(buffer); };

        rc = RegQueryValueExW(vs7_key, v, NULL, NULL, (LPBYTE)buffer, &cb_data);
        if (rc != 0)  continue;

        // @Robustness: Do the zero-termination thing suggested in the RegQueryValue docs?

        auto lib_path = concat(buffer, L"VC\\Lib\\amd64");

        // Check to see whether a vcruntime.lib actually exists here.
        auto vcruntime_filename = concat(lib_path, L"\\vcruntime.lib");
        defer { free(vcruntime_filename); };

        if (os_file_exists(vcruntime_filename)) {
            result->vs_exe_path     = concat(buffer, L"VC\\bin");
            result->vs_library_path = lib_path;
            return;
        }

        free(lib_path);
    }

    // If we get here, we failed to find anything.
}


Find_Result find_visual_studio_and_windows_sdk() {
    Find_Result result;

    find_windows_kit_root(&result);

    if (result.windows_sdk_root) {
        result.windows_sdk_um_library_path   = concat(result.windows_sdk_root, L"\\um\\x64");
        result.windows_sdk_ucrt_library_path = concat(result.windows_sdk_root, L"\\ucrt\\x64");
    }

    find_visual_studio_by_fighting_through_microsoft_craziness(&result);

    return result;
}
	//
	// Author: Jonathan Blow
	// Version: 1
	// Date: 31 August, 2018
	//
	// This code is released under the MIT license, which you can find at
	//
	// https://opensource.org/licenses/MIT
	//
	//
	//
	// See the comments for how to use this library just below the includes.
	//


	#include <windows.h>
	#include <stdlib.h>
	#include <string.h>
	#include <assert.h>
	#include <stdio.h>
	#include <sys/stat.h>

	#include <stdint.h>
	#include <io.h> // For _get_osfhandle


	//
	// HOW TO USE THIS CODE
	//
	// The purpose of this file is to find the folders that contain libraries
	// you may need to link against, on Windows, if you are linking with any
	// compiled C or C++ code. This will be necessary for many non-C++ programming
	// language environments that want to provide compatibility.
	//
	// We find the place where the Visual Studio libraries live (for example,
	// libvcruntime.lib), where the linker and compiler executables live
	// (for example, link.exe), and where the Windows SDK libraries reside
	// (kernel32.lib, libucrt.lib).
	//
	// We all wish you didn't have to worry about so many weird dependencies,
	// but we don't really have a choice about this, sadly.
	//
	// I don't claim that this is the absolute best way to solve this problem,
	// and so far we punt on things (if you have multiple versions of Visual Studio
	// installed, we return the first one, rather than the newest). But it
	// will solve the basic problem for you as simply as I know how to do it,
	// and because there isn't too much code here, it's easy to modify and expand.
	//
	//
	// Here is the API you need to know about:
	//

	struct Find_Result {
	int windows_sdk_version; // Zero if no Windows SDK found.

	wchar_t *windows_sdk_root = NULL;
	wchar_t *windows_sdk_um_library_path = NULL;
	wchar_t *windows_sdk_ucrt_library_path = NULL;

	wchar_t *vs_exe_path = NULL;
	wchar_t *vs_library_path = NULL;
	};

	Find_Result find_visual_studio_and_windows_sdk();

	void free_resources(Find_Result *result) {
	free(result->windows_sdk_root);
	free(result->windows_sdk_um_library_path);
	free(result->windows_sdk_ucrt_library_path);
	free(result->vs_exe_path);
	free(result->vs_library_path);
	}

	//
	// Call find_visual_studio_and_windows_sdk, look at the resulting
	// paths, then call free_resources on the result.
	//
	// Everything else in this file is implementation details that you
	// don't need to care about.
	//

	//
	// This file was about 400 lines before we started adding these comments.
	// You might think that's way too much code to do something as simple
	// as finding a few library and executable paths. I agree. However,
	// Microsoft's own solution to this problem, called "vswhere", is a
	// mere EIGHT THOUSAND LINE PROGRAM, spread across 70 files,
	// that they posted to github unironically.
	//
	// I am not making this up: https://github.com/Microsoft/vswhere
	//
	// Several people have therefore found the need to solve this problem
	// themselves. We referred to some of these other solutions when
	// figuring out what to do, most prominently ziglang's version,
	// by Ryan Saunderson.
	//
	// I hate this kind of code. The fact that we have to do this at all
	// is stupid, and the actual maneuvers we need to go through
	// are just painful. If programming were like this all the time,
	// I would quit.
	//
	// Because this is such an absurd waste of time, I felt it would be
	// useful to package the code in an easily-reusable way, in the
	// style of the stb libraries. We haven't gone as all-out as some
	// of the stb libraries do (which compile in C with no includes, often).
	// For this version you need C++ and the headers at the top of the file.
	//
	// We return the strings as Windows wide character strings. Aesthetically
	// I don't like that (I think most sane programs are UTF-8 internally),
	// but apparently, not all valid Windows file paths can even be converted
	// correctly to UTF-8. So have fun with that. It felt safest and simplest
	// to stay with wchar_t since all of this code is fully ensconced in
	// Windows crazy-land.
	//
	// One other shortcut I took is that this is hardcoded to return the
	// folders for x64 libraries. If you want x86 or arm, you can make
	// slight edits to the code below, or, if enough people want this,
	// I can work it in here.
	//

	// Defer macro/thing.

	#define CONCAT_INTERNAL(x,y) x##y
	#define CONCAT(x,y) CONCAT_INTERNAL(x,y)

	template<typename T>
	struct ExitScope {
	T lambda;
	ExitScope(T lambda):lambda(lambda){}
	~ExitScope(){lambda();}
	ExitScope(const ExitScope&);
	private:
	ExitScope& operator =(const ExitScope&);
	};

	class ExitScopeHelp {
	public:
	template<typename T>
	ExitScope<T> operator+(T t){ return t;}
	};

	#define defer const auto& CONCAT(defer__, __LINE__) = ExitScopeHelp() + [&]()


	// COM objects for the ridiculous Microsoft craziness.

	struct DECLSPEC_UUID("B41463C3-8866-43B5-BC33-2B0676F7F42E") DECLSPEC_NOVTABLE ISetupInstance : public IUnknown
	{
	STDMETHOD(GetInstanceId)(_Out_ BSTR* pbstrInstanceId) = 0;
	STDMETHOD(GetInstallDate)(_Out_ LPFILETIME pInstallDate) = 0;
	STDMETHOD(GetInstallationName)(_Out_ BSTR* pbstrInstallationName) = 0;
	STDMETHOD(GetInstallationPath)(_Out_ BSTR* pbstrInstallationPath) = 0;
	STDMETHOD(GetInstallationVersion)(_Out_ BSTR* pbstrInstallationVersion) = 0;
	STDMETHOD(GetDisplayName)(_In_ LCID lcid, _Out_ BSTR* pbstrDisplayName) = 0;
	STDMETHOD(GetDescription)(_In_ LCID lcid, _Out_ BSTR* pbstrDescription) = 0;
	STDMETHOD(ResolvePath)(_In_opt_z_ LPCOLESTR pwszRelativePath, _Out_ BSTR* pbstrAbsolutePath) = 0;
	};

	struct DECLSPEC_UUID("6380BCFF-41D3-4B2E-8B2E-BF8A6810C848") DECLSPEC_NOVTABLE IEnumSetupInstances : public IUnknown
	{
	STDMETHOD(Next)(_In_ ULONG celt, _Out_writes_to_(celt, pceltFetched) ISetupInstance* rgelt, _Out_opt_ _Deref_out_range_(0, celt) ULONG* pceltFetched) = 0;
	STDMETHOD(Skip)(_In_ ULONG celt) = 0;
	STDMETHOD(Reset)(void) = 0;
	STDMETHOD(Clone)(_Deref_out_opt_ IEnumSetupInstances** ppenum) = 0;
	};

	struct DECLSPEC_UUID("42843719-DB4C-46C2-8E7C-64F1816EFD5B") DECLSPEC_NOVTABLE ISetupConfiguration : public IUnknown
	{
	STDMETHOD(EnumInstances)(_Out_ IEnumSetupInstances** ppEnumInstances) = 0;
	STDMETHOD(GetInstanceForCurrentProcess)(_Out_ ISetupInstance** ppInstance) = 0;
	STDMETHOD(GetInstanceForPath)(_In_z_ LPCWSTR wzPath, _Out_ ISetupInstance** ppInstance) = 0;
	};


	// The beginning of the actual code that does things.

	struct Version_Data {
	int32_t best_version[4]; // For Windows 8 versions, only two of these numbers are used.
	wchar_t *best_name;
	};

	bool os_file_exists(wchar_t *name) {
	// @Robustness: What flags do we really want to check here?

	auto attrib = GetFileAttributesW(name);
	if (attrib == INVALID_FILE_ATTRIBUTES) return false;
	if (attrib & FILE_ATTRIBUTE_DIRECTORY) return false;

	return true;
	}

	wchar_t concat(wchar_t a, wchar_t b, wchar_t c = nullptr, wchar_t *d = nullptr) {
	// Concatenate up to 4 wide strings together. Allocated with malloc.
	// If you don't like that, use a programming language that actually
	// helps you with using custom allocators. Or just edit the code.

	auto len_a = wcslen(a);
	auto len_b = wcslen(b);

	auto len_c = 0;
	if (c) len_c = wcslen(c);

	auto len_d = 0;
	if (d) len_d = wcslen(d);

	wchar_t result = (wchar_t )malloc((len_a + len_b + len_c + len_d + 1) * 2);
	memcpy(result, a, len_a*2);
	memcpy(result + len_a, b, len_b*2);

	if (c) memcpy(result + len_a + len_b, c, len_c * 2);
	if (d) memcpy(result + len_a + len_b + len_c, d, len_d * 2);

	result[len_a + len_b + len_c + len_d] = 0;

	return result;
	}

	typedef void (Visit_Proc_W)(wchar_t short_name, wchar_t full_name, Version_Data data);
	bool visit_files_w(wchar_t dir_name, Version_Data data, Visit_Proc_W proc) {

	// Visit everything in one folder (non-recursively). If it's a directory
	// that doesn't start with ".", call the visit proc on it. The visit proc
	// will see if the filename conforms to the expected versioning pattern.

	auto wildcard_name = concat(dir_name, L"\\*");
	defer { free(wildcard_name); };

	WIN32_FIND_DATAW find_data;
	auto handle = FindFirstFileW(wildcard_name, &find_data);
	if (handle == INVALID_HANDLE_VALUE) return false;

	while (true) {
	if ((find_data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) && (find_data.cFileName[0] != '.')) {
	auto full_name = concat(dir_name, L"\\", find_data.cFileName);
	defer { free(full_name); };

	proc(find_data.cFileName, full_name, data);
	}

	auto success = FindNextFileW(handle, &find_data);
	if (!success) break;
	}

	FindClose(handle);

	return true;
	}


	wchar_t find_windows_kit_root(HKEY key, wchar_t version) {
	// Given a key to an already opened registry entry,
	// get the value stored under the 'version' subkey.
	// If that's not the right terminology, hey, I never do registry stuff.

	DWORD required_length;
	auto rc = RegQueryValueExW(key, version, NULL, NULL, NULL, &required_length);
	if (rc != 0) return NULL;

	DWORD length = required_length + 2; // The +2 is for the maybe optional zero later on. Probably we are over-allocating.
	wchar_t value = (wchar_t )malloc(length);
	if (!value) return NULL;

	rc = RegQueryValueExW(key, version, NULL, NULL, (LPBYTE)value, &length); // We know that version is zero-terminated...
	if (rc != 0) return NULL;

	// The documentation says that if the string for some reason was not stored
	// with zero-termination, we need to manually terminate it. Sigh!!

	if (value[length]) {
	value[length+1] = 0;
	}

	return value;
	}

	void win10_best(wchar_t short_name, wchar_t full_name, Version_Data *data) {
	// Find the Windows 10 subdirectory with the highest version number.

	int i0, i1, i2, i3;
	auto success = swscanf_s(short_name, L"%d.%d.%d.%d", &i0, &i1, &i2, &i3);
	if (success < 4) return;

	if (i0 < data->best_version[0]) return;
	else if (i0 == data->best_version[0]) {
	if (i1 < data->best_version[1]) return;
	else if (i1 == data->best_version[1]) {
	if (i2 < data->best_version[2]) return;
	else if (i2 == data->best_version[2]) {
	if (i3 < data->best_version[3]) return;
	}
	}
	}

	// we have to copy_string and free here because visit_files free's the full_name string
	// after we execute this function, so Win*_Data would contain an invalid pointer.
	if (data->best_name) free(data->best_name);
	data->best_name = _wcsdup(full_name);

	if (data->best_name) {
	data->best_version[0] = i0;
	data->best_version[1] = i1;
	data->best_version[2] = i2;
	data->best_version[3] = i3;
	}
	}

	void win8_best(wchar_t short_name, wchar_t full_name, Version_Data *data) {
	// Find the Windows 8 subdirectory with the highest version number.

	int i0, i1;
	auto success = swscanf_s(short_name, L"winv%d.%d", &i0, &i1);
	if (success < 2) return;

	if (i0 < data->best_version[0]) return;
	else if (i0 == data->best_version[0]) {
	if (i1 < data->best_version[1]) return;
	}

	// we have to copy_string and free here because visit_files free's the full_name string
	// after we execute this function, so Win*_Data would contain an invalid pointer.
	if (data->best_name) free(data->best_name);
	data->best_name = _wcsdup(full_name);

	if (data->best_name) {
	data->best_version[0] = i0;
	data->best_version[1] = i1;
	}
	}

	void find_windows_kit_root(Find_Result *result) {
	// Information about the Windows 10 and Windows 8 development kits
	// is stored in the same place in the registry. We open a key
	// to that place, first checking preferntially for a Windows 10 kit,
	// then, if that's not found, a Windows 8 kit.

	HKEY main_key;

	auto rc = RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\Windows Kits\\Installed Roots",
	0, KEY_QUERY_VALUE \| KEY_WOW64_32KEY \| KEY_ENUMERATE_SUB_KEYS, &main_key);
	if (rc != S_OK) return;
	defer { RegCloseKey(main_key); };

	// Look for a Windows 10 entry.
	auto windows10_root = find_windows_kit_root(main_key, L"KitsRoot10");

	if (windows10_root) {
	defer { free(windows10_root); };
	Version_Data data = {0};
	auto windows10_lib = concat(windows10_root, L"Lib");
	defer { free(windows10_lib); };

	visit_files_w(windows10_lib, &data, win10_best);
	if (data.best_name) {
	result->windows_sdk_version = 10;
	result->windows_sdk_root = data.best_name;
	return;
	}
	}

	// Look for a Windows 8 entry.
	auto windows8_root = find_windows_kit_root(main_key, L"KitsRoot81");

	if (windows8_root) {
	defer { free(windows8_root); };

	auto windows8_lib = concat(windows8_root, L"Lib");
	defer { free(windows8_lib); };

	Version_Data data = {0};
	visit_files_w(windows8_lib, &data, win8_best);
	if (data.best_name) {
	result->windows_sdk_version = 8;
	result->windows_sdk_root = data.best_name;
	return;
	}
	}

	// If we get here, we failed to find anything.
	}


	void find_visual_studio_by_fighting_through_microsoft_craziness(Find_Result *result) {
	// The name of this procedure is kind of cryptic. Its purpose is
	// to fight through Microsoft craziness. The things that the fine
	// Visual Studio team want you to do, JUST TO FIND A SINGLE FOLDER
	// THAT EVERYONE NEEDS TO FIND, are ridiculous garbage.

	// For earlier versions of Visual Studio, you'd find this information in the registry,
	// similarly to the Windows Kits above. But no, now it's the future, so to ask the
	// question "Where is the Visual Studio folder?" you have to do a bunch of COM object
	// instantiation, enumeration, and querying. (For extra bonus points, try doing this in
	// a new, underdeveloped programming language where you don't have COM routines up
	// and running yet. So fun.)
	//
	// If all this COM object instantiation, enumeration, and querying doesn't give us
	// a useful result, we drop back to the registry-checking method.

	auto rc = CoInitialize(NULL);
	// "Subsequent valid calls return false." So ignore false.
	// if rc != S_OK return false;

	GUID my_uid = {0x42843719, 0xDB4C, 0x46C2, {0x8E, 0x7C, 0x64, 0xF1, 0x81, 0x6E, 0xFD, 0x5B}};
	GUID CLSID_SetupConfiguration = {0x177F0C4A, 0x1CD3, 0x4DE7, {0xA3, 0x2C, 0x71, 0xDB, 0xBB, 0x9F, 0xA3, 0x6D}};

	ISetupConfiguration *config = NULL;
	auto hr = CoCreateInstance(CLSID_SetupConfiguration, NULL, CLSCTX_INPROC_SERVER, my_uid, (void **)&config);
	if (hr != 0) return;
	defer { config->Release(); };

	IEnumSetupInstances *instances = NULL;
	hr = config->EnumInstances(&instances);
	if (hr != 0) return;
	if (!instances) return;
	defer { instances->Release(); };

	while (1) {
	ULONG found = 0;
	ISetupInstance *instance = NULL;
	auto hr = instances->Next(1, &instance, &found);
	if (hr != S_OK) break;

	defer { instance->Release(); };

	BSTR bstr_inst_path;
	hr = instance->GetInstallationPath(&bstr_inst_path);
	if (hr != S_OK) continue;
	defer { SysFreeString(bstr_inst_path); };

	auto tools_filename = concat(bstr_inst_path, L"\\VC\\Auxiliary\\Build\\Microsoft.VCToolsVersion.default.txt");
	defer { free(tools_filename); };

	FILE *f = nullptr;
	auto open_result = _wfopen_s(&f, tools_filename, L"rt");
	if (open_result != 0) continue;
	if (!f) continue;
	defer { fclose(f); };

	LARGE_INTEGER tools_file_size;
	auto file_handle = (HANDLE)_get_osfhandle(_fileno(f));
	BOOL success = GetFileSizeEx(file_handle, &tools_file_size);
	if (!success) continue;

	auto version_bytes = (tools_file_size.QuadPart + 1) * 2; // Warning: This multiplication by 2 presumes there is no variable-length encoding in the wchars (wacky characters in the file could betray this expectation).
	wchar_t version = (wchar_t )malloc(version_bytes);
	defer { free(version); };

	auto read_result = fgetws(version, version_bytes, f);
	if (!read_result) continue;

	auto version_tail = wcschr(version, '\n');
	if (version_tail) *version_tail = 0; // Stomp the data, because nobody cares about it.

	auto library_path = concat(bstr_inst_path, L"\\VC\\Tools\\MSVC\\", version, L"\\lib\\x64");
	auto library_file = concat(library_path, L"\\vcruntime.lib"); // @Speed: Could have library_path point to this string, with a smaller count, to save on memory flailing!

	if (os_file_exists(library_file)) {
	auto link_exe_path = concat(bstr_inst_path, L"\\VC\\Tools\\MSVC\\", version, L"\\bin\\Hostx64\\x64");
	result->vs_exe_path = link_exe_path;
	result->vs_library_path = library_path;
	return;
	}

	/*
	Ryan Saunderson said:
	"Clang uses the 'SetupInstance->GetInstallationVersion' / ISetupHelper->ParseVersion to find the newest version
	and then reads the tools file to define the tools path - which is definitely better than what i did."

	So... @Incomplete: Should probably pick the newest version...
	*/
	}

	// If we get here, we didn't find Visual Studio 2017. Try earlier versions.

	HKEY vs7_key;
	rc = RegOpenKeyExA(HKEY_LOCAL_MACHINE, "SOFTWARE\\Microsoft\\VisualStudio\\SxS\\VS7", 0, KEY_QUERY_VALUE \| KEY_WOW64_32KEY, &vs7_key);

	if (rc != S_OK) return;
	defer { RegCloseKey(vs7_key); };

	// Hardcoded search for 4 prior Visual Studio versions. Is there something better to do here?
	wchar_t *versions[] = { L"14.0", L"12.0", L"11.0", L"10.0" };
	const int NUM_VERSIONS = sizeof(versions) / sizeof(versions[0]);

	for (int i = 0; i < NUM_VERSIONS; i++) {
	auto v = versions[i];

	DWORD dw_type;
	DWORD cb_data;

	auto rc = RegQueryValueExW(vs7_key, v, NULL, &dw_type, NULL, &cb_data);
	if ((rc == ERROR_FILE_NOT_FOUND) \|\| (dw_type != REG_SZ)) {
	continue;
	}

	auto buffer = (wchar_t *)malloc(cb_data);
	if (!buffer) return;
	defer { free(buffer); };

	rc = RegQueryValueExW(vs7_key, v, NULL, NULL, (LPBYTE)buffer, &cb_data);
	if (rc != 0) continue;

	// @Robustness: Do the zero-termination thing suggested in the RegQueryValue docs?

	auto lib_path = concat(buffer, L"VC\\Lib\\amd64");

	// Check to see whether a vcruntime.lib actually exists here.
	auto vcruntime_filename = concat(lib_path, L"\\vcruntime.lib");
	defer { free(vcruntime_filename); };

	if (os_file_exists(vcruntime_filename)) {
	result->vs_exe_path = concat(buffer, L"VC\\bin");
	result->vs_library_path = lib_path;
	return;
	}

	free(lib_path);
	}

	// If we get here, we failed to find anything.
	}


	Find_Result find_visual_studio_and_windows_sdk() {
	Find_Result result;

	find_windows_kit_root(&result);

	if (result.windows_sdk_root) {
	result.windows_sdk_um_library_path = concat(result.windows_sdk_root, L"\\um\\x64");
	result.windows_sdk_ucrt_library_path = concat(result.windows_sdk_root, L"\\ucrt\\x64");
	}

	find_visual_studio_by_fighting_through_microsoft_craziness(&result);

	return result;
	}