Added functions for detecting known folders per-platform. Not tested on Windows yet, but who cares?

SModule

@@ -13,6 +13,7 @@ mijin_sources = Split("""
     source/mijin/net/http.cpp
     source/mijin/net/ip.cpp
     source/mijin/net/socket.cpp
+    source/mijin/platform/folders.cpp
     source/mijin/util/os.cpp
     source/mijin/types/name.cpp
     source/mijin/virtual_filesystem/filesystem.cpp

source/mijin/platform/.idea/.gitignore

@@ -0,0 +1,6 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

source/mijin/platform/.idea/modules.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/platform.iml" filepath="$PROJECT_DIR$/.idea/platform.iml" />
+    </modules>
+  </component>
+</project>

source/mijin/platform/.idea/platform.iml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="CPP_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$" />
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>

source/mijin/platform/folders.cpp

@@ -0,0 +1,106 @@
+
+#include "./folders.hpp"
+
+
+#include "../detect.hpp"
+#include "../debug/assert.hpp"
+
+#include <cstdlib>
+
+#if MIJIN_TARGET_OS == MIJIN_OS_WINDOWS
+#   include <Shlobj.h>
+#endif
+
+namespace mijin
+{
+fs::path getKnownFolder(KnownFolder folder) MIJIN_NOEXCEPT
+{
+#if MIJIN_TARGET_OS == MIJIN_OS_LINUX
+    switch (folder)
+    {
+    case KnownFolder::USER_HOME:
+        if (const char* val = std::getenv("HOME"); val != nullptr)
+        {
+            return val;
+        }
+        return "/";
+    case KnownFolder::TEMP:
+        for (const char* varname : {"TMPDIR", "TEMP", "TMP"})
+        {
+            if (const char* val = std::getenv(varname); val != nullptr)
+            {
+                return val;
+            }
+        }
+        return "/tmp";
+    case KnownFolder::CACHE_ROOT:
+        if (const char* val = std::getenv("XDG_CACHE_HOME"); val != nullptr)
+        {
+            return val;
+        }
+        return getKnownFolder(KnownFolder::USER_HOME) / ".cache";
+    case KnownFolder::USER_CONFIG_ROOT:
+        if (const char* val = std::getenv("XDG_CONFIG_HOME"); val != nullptr)
+        {
+            return val;
+        }
+        return getKnownFolder(KnownFolder::USER_HOME) / ".config";
+    case KnownFolder::USER_DATA_ROOT:
+        if (const char* val = std::getenv("XDG_DATA_HOME"); val != nullptr)
+        {
+            return val;
+        }
+        return getKnownFolder(KnownFolder::USER_HOME) / ".local/share";
+    }
+    MIJIN_ERROR("Invalid value passed to getKnownFolder().");
+    return {};
+#elif MIJIN_TARGET_OS == MIJIN_OS_WINDOWS
+    // TODO: this is 100% untested on Windows
+
+    auto getKnownFolderPath = [](REFKNOWNFOLDERID rfid) -> fs::path
+    {
+        WSTR path = nullptr;
+        if (!SUCCEEDED(SHGetKnownFolderPath(rfid, KF_FLAG_DEFAULT, nullptr, &path)))
+        {
+            CoTaskMemFree(path);
+            return {};
+        }
+        fs::path result(path);
+        CoTaskMemFree(path);
+        return result;
+    };
+
+    switch (folder)
+    {
+    case KnownFolder::USER_HOME:
+        if (const fs::path path = getKnownFolderPath(FOLDERID_Profile); !path.empty())
+        {
+            return path;
+        }
+        return "C:\\";
+    case KnownFolder::TEMP:
+    case KnownFolder::CACHE_ROOT:
+        for (const char* varname : {"TMPDIR", "TEMP", "TMP"})
+        {
+            if (const char* val = std::getenv(varname); val != nullptr)
+            {
+                return val;
+            }
+        }
+        return getKnownFolder(KnownFolder::USER_DATA_ROOT) / "Temp";
+    case KnownFolder::USER_CONFIG_ROOT:
+    case KnownFolder::USER_DATA_ROOT:
+        if (const fs::path path = getKnownFolderPath(FOLDERID_LocalAppData); !path.empty())
+        {
+            return path;
+        }
+        return getKnownFolder(KnownFolder::USER_HOME) / "AppData" / "Local";
+    }
+    MIJIN_ERROR("Invalid value passed to getKnownFolder().");
+    return {};
+#else
+    MIJIN_ERROR("Known folders not implemented for this platform.");
+    return {}; // don't know :/
+#endif
+}
+}

source/mijin/platform/folders.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#if !defined(MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED)
+#define MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED 1
+
+#include "../internal/common.hpp"
+
+#include <filesystem>
+
+namespace fs = std::filesystem;
+
+namespace mijin
+{
+enum class KnownFolder
+{
+    USER_HOME,
+    TEMP,
+    CACHE_ROOT,
+    USER_CONFIG_ROOT,
+    USER_DATA_ROOT
+};
+
+[[nodiscard]]
+fs::path getKnownFolder(KnownFolder folder) MIJIN_NOEXCEPT;
+}
+
+#endif // defined(MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED)

source/mijin/virtual_filesystem/filesystem.cpp

@@ -1,6 +1,8 @@
 
 #include "./filesystem.hpp"
 
+#include "../platform/folders.hpp"
+
 namespace mijin
 {
 
@@ -37,7 +39,7 @@ std::vector<fs::path> OSFileSystemAdapter::getRoots()
 
 fs::path OSFileSystemAdapter::getHomeFolder()
 {
-    return "/home/mewin"; // very TODO
+    return getKnownFolder(KnownFolder::USER_HOME);
 }
 
 std::vector<FileInfo> OSFileSystemAdapter::listFiles(const fs::path& folder)