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feat: add msvc.cppm — robust Visual Studio / MSVC STL discovery
New module mcpp.toolchain.msvc with three discovery strategies: 1. vswhere.exe (Microsoft's official VS locator) — most reliable 2. Environment variables (VSINSTALLDIR, VS*COMNTOOLS) 3. Well-known paths (VS 2017-2025, all editions + BuildTools) Replaces the hardcoded VS2022 path in clang.cppm with msvc::find_std_module_source(). Fixes "no std module source" error on machines with non-standard VS installations. Also provides find_cl() for future MSVC toolchain support.
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‎.agents/docs/2026-05-20-msvc-stl-discovery-plan.md‎

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# MSVC STL Discovery — msvc.cppm 模块设计
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## 问题
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mcpp 在 Windows 上查找 `import std` 的 MSVC STL `std.ixx` 时硬编码了
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`C:\Program Files\Microsoft Visual Studio\2022`，导致非标准 VS 安装找不到。
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## 方案
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新建 `src/toolchain/msvc.cppm` 模块，提供 MSVC/Visual Studio 发现能力。
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### 查找策略（按优先级）
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1. **vswhere.exe** — 微软官方 VS 安装发现工具，最可靠
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- 路径: `C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe`
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- 命令: `vswhere -latest -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 -property installationPath`
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- 返回: VS 安装路径如 `C:\Program Files\Microsoft Visual Studio\2022\Community`
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2. **环境变量** — `VSINSTALLDIR`、`VS170COMNTOOLS`(2022)、`VS160COMNTOOLS`(2019)
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- 从 `VSINSTALLDIR` 直接得到 VS 根目录
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- 从 `VS*COMNTOOLS` 向上推算
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3. **固定路径扫描** — 兜底方案
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- `C:\Program Files\Microsoft Visual Studio\{2025,2022,2019}\{Enterprise,Professional,Community,BuildTools}`
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- `C:\Program Files (x86)\Microsoft Visual Studio\{2019,2017}\...`
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### std.ixx 路径推算
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从 VS 安装路径推算:
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```
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<VS_ROOT>/VC/Tools/MSVC/<version>/modules/std.ixx
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```
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`<version>` 通过遍历 `VC/Tools/MSVC/` 目录取最新版本。
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### 模块接口
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```cpp
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export module mcpp.toolchain.msvc;
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import std;
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export namespace mcpp::toolchain::msvc {
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// 查找 VS 安装路径（返回最新版本）
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std::optional<std::filesystem::path> find_vs_install_path();
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// 查找 MSVC 工具链根目录 (VC/Tools/MSVC/<ver>/)
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std::optional<std::filesystem::path> find_msvc_tools_dir();
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// 查找 std.ixx 模块源文件
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std::optional<std::filesystem::path> find_std_module_source();
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// 查找 cl.exe（未来 MSVC 工具链支持用）
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std::optional<std::filesystem::path> find_cl();
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}
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```
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### 改动点
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1. 新建 `src/toolchain/msvc.cppm`
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2. `src/toolchain/clang.cppm` — `enrich_toolchain` 中的硬编码 VS 路径改为调用 `msvc::find_std_module_source()`

‎src/toolchain/clang.cppm‎

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import std;
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import mcpp.toolchain.model;
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import mcpp.toolchain.msvc;
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import mcpp.toolchain.probe;
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import mcpp.xlings;
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import mcpp.platform;
@@ -146,26 +147,11 @@ void enrich_toolchain(Toolchain& tc, const std::string& envPrefix) {
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#if defined(_WIN32)
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// Fallback: if libc++ std.cppm not found, look for MSVC STL's std.ixx.
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// This happens when Clang targets x86_64-pc-windows-msvc.
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// Uses msvc.cppm which searches via vswhere, env vars, and known paths.
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if (!tc.hasImportStd && msvTarget) {
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// Search Visual Studio installations for std.ixx
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// Typical path: C:\Program Files\Microsoft Visual Studio\2022\*\VC\Tools\MSVC\*\modules\std.ixx
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std::error_code ec;
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std::filesystem::path vsBase = "C:\\Program Files\\Microsoft Visual Studio\\2022";
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if (std::filesystem::exists(vsBase, ec)) {
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for (auto& edition : std::filesystem::directory_iterator(vsBase, ec)) {
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auto vcTools = edition.path() / "VC" / "Tools" / "MSVC";
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if (!std::filesystem::exists(vcTools, ec)) continue;
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for (auto& ver : std::filesystem::directory_iterator(vcTools, ec)) {
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auto stdIxx = ver.path() / "modules" / "std.ixx";
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if (std::filesystem::exists(stdIxx, ec)) {
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tc.stdModuleSource = stdIxx;
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tc.hasImportStd = true;
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break;
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}
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}
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if (tc.hasImportStd) break;
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}
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if (auto p = mcpp::toolchain::msvc::find_std_module_source()) {
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tc.stdModuleSource = *p;
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tc.hasImportStd = true;
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}
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}
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#endif

‎src/toolchain/msvc.cppm‎

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// mcpp.toolchain.msvc — MSVC / Visual Studio discovery on Windows.
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//
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// Provides reliable discovery of Visual Studio installations and MSVC
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// toolchain components (std.ixx, cl.exe, lib.exe, etc.) using multiple
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// strategies:
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// 1. vswhere.exe (Microsoft's official VS locator)
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// 2. Environment variables (VSINSTALLDIR, VS*COMNTOOLS)
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// 3. Well-known installation paths (fallback)
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//
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// This module is used by clang.cppm to find MSVC STL's std.ixx when
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// Clang targets x86_64-pc-windows-msvc. It will also serve as the
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// foundation for future native MSVC (cl.exe) toolchain support.
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module;
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#include <cstdio>
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#include <cstdlib>
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#if defined(_WIN32)
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#define popen _popen
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#define pclose _pclose
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#endif
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export module mcpp.toolchain.msvc;
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import std;
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export namespace mcpp::toolchain::msvc {
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// Find a Visual Studio installation path (returns the newest found).
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std::optional<std::filesystem::path> find_vs_install_path();
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// Find the MSVC tools directory: <VS>/VC/Tools/MSVC/<latest_version>/
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std::optional<std::filesystem::path> find_msvc_tools_dir();
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// Find MSVC STL's std.ixx module source file.
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std::optional<std::filesystem::path> find_std_module_source();
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// Find cl.exe (for future MSVC toolchain support).
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std::optional<std::filesystem::path> find_cl();
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} // namespace mcpp::toolchain::msvc
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namespace mcpp::toolchain::msvc {
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namespace {
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#if defined(_WIN32)
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// Run a command and capture stdout (first line, trimmed).
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std::string run_capture_line(const std::string& cmd) {
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std::array<char, 4096> buf{};
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std::string out;
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std::FILE* fp = ::popen(cmd.c_str(), "r");
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if (!fp) return {};
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while (std::fgets(buf.data(), buf.size(), fp) != nullptr)
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out += buf.data();
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::pclose(fp);
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// Trim trailing whitespace/newlines
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while (!out.empty() && (out.back() == '\n' || out.back() == '\r' || out.back() == ' '))
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out.pop_back();
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// Take first line only
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auto nl = out.find('\n');
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if (nl != std::string::npos) out.resize(nl);
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return out;
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}
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// Strategy 1: Use vswhere.exe to find VS installation.
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std::optional<std::filesystem::path> find_vs_via_vswhere() {
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// vswhere.exe ships with the VS Installer at a well-known path
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std::filesystem::path vswhere =
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"C:\\Program Files (x86)\\Microsoft Visual Studio\\Installer\\vswhere.exe";
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if (!std::filesystem::exists(vswhere)) return std::nullopt;
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auto result = run_capture_line(
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"\"" + vswhere.string() + "\" -latest -products * "
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"-requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 "
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"-property installationPath 2>nul");
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if (!result.empty() && std::filesystem::exists(result))
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return std::filesystem::path(result);
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return std::nullopt;
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}
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// Strategy 2: Use environment variables.
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std::optional<std::filesystem::path> find_vs_via_env() {
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// VSINSTALLDIR is set inside VS Developer Command Prompt
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if (auto* dir = std::getenv("VSINSTALLDIR"); dir && *dir) {
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std::filesystem::path p{dir};
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if (std::filesystem::exists(p / "VC" / "Tools" / "MSVC"))
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return p;
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}
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// VS*COMNTOOLS: VS170COMNTOOLS (2022), VS160COMNTOOLS (2019), VS150COMNTOOLS (2017)
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for (auto* var : {"VS170COMNTOOLS", "VS160COMNTOOLS", "VS150COMNTOOLS"}) {
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if (auto* val = std::getenv(var); val && *val) {
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// Common7/Tools/ → go up two levels to VS root
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std::filesystem::path p{val};
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auto root = p.parent_path().parent_path();
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if (std::filesystem::exists(root / "VC" / "Tools" / "MSVC"))
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return root;
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}
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}
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return std::nullopt;
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}
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// Strategy 3: Scan well-known paths.
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std::optional<std::filesystem::path> find_vs_via_paths() {
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static constexpr std::string_view bases[] = {
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"C:\\Program Files\\Microsoft Visual Studio",
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"C:\\Program Files (x86)\\Microsoft Visual Studio",
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};
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static constexpr std::string_view years[] = {"2025", "2022", "2019", "2017"};
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static constexpr std::string_view editions[] = {
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"Enterprise", "Professional", "Community", "BuildTools", "Preview"
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};
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std::error_code ec;
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for (auto base : bases) {
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for (auto year : years) {
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for (auto edition : editions) {
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auto p = std::filesystem::path(base) / std::string(year) / std::string(edition);
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if (std::filesystem::exists(p / "VC" / "Tools" / "MSVC", ec))
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return p;
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}
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}
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}
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return std::nullopt;
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}
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// From a VS install path, find the latest MSVC tools version directory.
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std::optional<std::filesystem::path> find_latest_msvc_tools(const std::filesystem::path& vsRoot) {
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auto vcTools = vsRoot / "VC" / "Tools" / "MSVC";
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std::error_code ec;
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if (!std::filesystem::exists(vcTools, ec)) return std::nullopt;
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std::filesystem::path latest;
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std::string latestVer;
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for (auto& entry : std::filesystem::directory_iterator(vcTools, ec)) {
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if (!entry.is_directory()) continue;
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auto ver = entry.path().filename().string();
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if (ver > latestVer) {
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latestVer = ver;
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latest = entry.path();
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}
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}
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return latest.empty() ? std::nullopt : std::optional{latest};
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}
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#endif // _WIN32
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} // namespace
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std::optional<std::filesystem::path> find_vs_install_path() {
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#if defined(_WIN32)
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// Try strategies in order of reliability
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if (auto p = find_vs_via_vswhere()) return p;
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if (auto p = find_vs_via_env()) return p;
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if (auto p = find_vs_via_paths()) return p;
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#endif
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return std::nullopt;
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}
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std::optional<std::filesystem::path> find_msvc_tools_dir() {
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#if defined(_WIN32)
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auto vs = find_vs_install_path();
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if (!vs) return std::nullopt;
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return find_latest_msvc_tools(*vs);
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#else
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return std::nullopt;
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#endif
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}
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std::optional<std::filesystem::path> find_std_module_source() {
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#if defined(_WIN32)
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auto tools = find_msvc_tools_dir();
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if (!tools) return std::nullopt;
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auto stdIxx = *tools / "modules" / "std.ixx";
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if (std::filesystem::exists(stdIxx))
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return stdIxx;
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#endif
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return std::nullopt;
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}
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std::optional<std::filesystem::path> find_cl() {
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#if defined(_WIN32)
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auto tools = find_msvc_tools_dir();
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if (!tools) return std::nullopt;
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// cl.exe is at <tools>/bin/Hostx64/x64/cl.exe
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auto cl = *tools / "bin" / "Hostx64" / "x64" / "cl.exe";
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if (std::filesystem::exists(cl))
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return cl;
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#endif
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return std::nullopt;
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}
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} // namespace mcpp::toolchain::msvc

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