[vcpkg] Use XDG/LOCALAPPDATA for default binary caching path

toolsrc/include/vcpkg/base/system.h

@@ -9,7 +9,14 @@ namespace vcpkg::System
 {
     Optional<std::string> get_environment_variable(ZStringView varname) noexcept;
 
-    ExpectedS<std::string> get_home_dir() noexcept;
+    const ExpectedS<fs::path>& get_home_dir() noexcept;
+
+    const ExpectedS<fs::path>& get_platform_cache_home() noexcept;
+
+    const ExpectedS<fs::path>& get_appdata_local() noexcept;
+    const ExpectedS<fs::path>& get_xdg_config_home() noexcept;
+    const ExpectedS<fs::path>& get_xdg_cache_home() noexcept;
+    const ExpectedS<fs::path>& get_xdg_data_home() noexcept;
 
     Optional<std::string> get_registry_string(void* base_hkey, StringView subkey, StringView valuename);
 

toolsrc/src/vcpkg/base/system.cpp

@@ -84,6 +84,15 @@ namespace vcpkg
         return supported_architectures;
     }
 
+    const ExpectedS<fs::path>& System::get_platform_cache_home() noexcept
+    {
+#ifdef _WIN32
+        return System::get_appdata_local();
+#else
+        return System::get_xdg_cache_home();
+#endif
+    }
+
     Optional<std::string> System::get_environment_variable(ZStringView varname) noexcept
     {
 #if defined(_WIN32)
@@ -105,17 +114,100 @@ namespace vcpkg
 #endif // defined(_WIN32)
     }
 
-    ExpectedS<std::string> System::get_home_dir() noexcept
+    const ExpectedS<fs::path>& System::get_home_dir() noexcept
     {
+        static ExpectedS<fs::path> s_home = []() -> ExpectedS<fs::path> {
 #ifdef _WIN32
-        auto maybe_home = System::get_environment_variable("USERPROFILE");
-        if (!maybe_home.has_value() || maybe_home.get()->empty())
-            return {"unable to read %USERPROFILE%", ExpectedRightTag{}};
+#define HOMEVAR "%USERPROFILE%"
+            auto maybe_home = System::get_environment_variable("USERPROFILE");
+            if (!maybe_home.has_value() || maybe_home.get()->empty())
+                return {"unable to read " HOMEVAR, ExpectedRightTag{}};
 #else
-        auto maybe_home = System::get_environment_variable("HOME");
-        if (!maybe_home.has_value() || maybe_home.get()->empty()) return {"unable to read $HOME", ExpectedRightTag{}};
+#define HOMEVAR "$HOME"
+            auto maybe_home = System::get_environment_variable("HOME");
+            if (!maybe_home.has_value() || maybe_home.get()->empty())
+                return {"unable to read " HOMEVAR, ExpectedRightTag{}};
 #endif
-        return {std::move(*maybe_home.get()), ExpectedLeftTag{}};
+
+            auto p = fs::u8path(*maybe_home.get());
+            if (!p.is_absolute()) return {HOMEVAR " was not an absolute path", ExpectedRightTag{}};
+
+            return {std::move(p), ExpectedLeftTag{}};
+        }();
+        return s_home;
+#undef HOMEVAR
+    }
+
+    const ExpectedS<fs::path>& System::get_appdata_local() noexcept
+    {
+        static ExpectedS<fs::path> s_home = []() -> ExpectedS<fs::path> {
+            auto maybe_home = System::get_environment_variable("LOCALAPPDATA");
+            if (!maybe_home.has_value() || maybe_home.get()->empty())
+                return {"unable to read %LOCALAPPDATA%", ExpectedRightTag{}};
+
+            auto p = fs::u8path(*maybe_home.get());
+            if (!p.is_absolute()) return {"%LOCALAPPDATA% was not an absolute path", ExpectedRightTag{}};
+
+            return {std::move(p), ExpectedLeftTag{}};
+        }();
+        return s_home;
+    }
+
+    const ExpectedS<fs::path>& get_xdg_config_home() noexcept
+    {
+        static ExpectedS<fs::path> s_home = [] {
+            auto maybe_home = System::get_environment_variable("XDG_CONFIG_HOME");
+            if (auto p = maybe_home.get())
+            {
+                return ExpectedS<fs::path>(fs::u8path(*p));
+            }
+            else
+            {
+                return System::get_home_dir().map([](fs::path home) {
+                    home.append(".config");
+                    return home;
+                });
+            }
+        }();
+        return s_home;
+    }
+
+    const ExpectedS<fs::path>& get_xdg_cache_home() noexcept
+    {
+        static ExpectedS<fs::path> s_home = [] {
+            auto maybe_home = System::get_environment_variable("XDG_CACHE_HOME");
+            if (auto p = maybe_home.get())
+            {
+                return ExpectedS<fs::path>(fs::u8path(*p));
+            }
+            else
+            {
+                return System::get_home_dir().map([](fs::path home) {
+                    home.append(".cache");
+                    return home;
+                });
+            }
+        }();
+        return s_home;
+    }
+
+    const ExpectedS<fs::path>& get_xdg_data_home() noexcept
+    {
+        static ExpectedS<fs::path> s_home = [] {
+            auto maybe_home = System::get_environment_variable("XDG_DATA_HOME");
+            if (auto p = maybe_home.get())
+            {
+                return ExpectedS<fs::path>(fs::u8path(*p));
+            }
+            else
+            {
+                return System::get_home_dir().map([](fs::path home) {
+                    home.append(".local").append(".share");
+                    return home;
+                });
+            }
+        }();
+        return s_home;
     }
 
 #if defined(_WIN32)

toolsrc/src/vcpkg/binarycaching.cpp

@@ -392,10 +392,11 @@ ExpectedS<std::unique_ptr<IBinaryProvider>> vcpkg::create_binary_provider_from_c
                     return add_error("unexpected arguments: binary config 'default' does not take more than 1 argument",
                                      segments[0].first);
 
-                auto maybe_home = System::get_home_dir();
+                auto&& maybe_home = System::get_platform_cache_home();
                 if (!maybe_home.has_value()) return add_error(maybe_home.error(), segments[0].first);
 
-                auto p = fs::u8path(maybe_home.value_or_exit(VCPKG_LINE_INFO)) / fs::u8path(".vcpkg/archives");
+                auto p = *maybe_home.get();
+                p.append("vcpkg").append("archives");
                 if (!p.is_absolute())
                     return add_error("default path was not absolute: " + p.u8string(), segments[0].first);
                 if (segments.size() == 2)