Starts to implement windows GUID part.

.gitignore

@@ -0,0 +1 @@
+zig-cache

known-folders.zig

@@ -1,39 +1,118 @@
 const std = @import("std");
 
 pub const SpecialFolder = enum {
-  home,
-  documents,
-  pictures,
-  music,
-  videos,
-  templates,
-  desktop,
-  downloads,
-  public,
-  fonts,
-  app_menu,
-  cache,
-  roaming_configuration,
-  local_configuration,
-  data,
-  system_folder,
-  runtime,
+    home,
+    documents,
+    pictures,
+    music,
+    videos,
+    templates,
+    desktop,
+    downloads,
+    public,
+    fonts,
+    app_menu,
+    cache,
+    roaming_configuration,
+    local_configuration,
+    data,
+    system_folder,
+    runtime,
 };
 
 // Explicitly define possible errors to make it clearer what callers need to handle
-pub const Error = error {
-  // TODO: fill this in
-	OutOfMemory,
-};
+pub const Error = error{
+// TODO: fill this in
+OutOfMemory};
 
 /// Returns a directory handle, or, if the folder does not exist, `null`.
 pub fn open(allocator: *std.mem.Allocator, folder: SpecialFolder) Error!?std.fs.Dir {
-  // TODO: Implement this
-  unreachable;
+    // TODO: Implement this
+    unreachable;
 }
 
 /// Returns the path to the folder or, if the folder does not exist, `null`.
 pub fn getPath(allocator: *std.mem.Allocator, folder: SpecialFolder) Error!?[]const u8 {
-  // TODO: Implement this
-  unreachable;
+    // TODO: Implement this
+    unreachable;
+}
+
+/// Contains the GUIDs for each available known-folder on windows
+const WindowsFolderSpec = union(enum) {
+    by_guid: std.os.windows.GUID,
+    by_env: struct {
+        root: []const u8,
+        subdirs: []const []const u8,
+    },
+};
+
+/// This returns a struct type with one field per SpecialFolder of type `T`.
+/// used for storing different config data per field
+fn SpecialFolderConfig(comptime T: type) type {
+    return struct {
+        const Self = @This();
+
+        home: T,
+        documents: T,
+        pictures: T,
+        music: T,
+        videos: T,
+        templates: T,
+        desktop: T,
+        downloads: T,
+        public: T,
+        fonts: T,
+        app_menu: T,
+        cache: T,
+        roaming_configuration: T,
+        local_configuration: T,
+        data: T,
+        system_folder: T,
+        runtime: T,
+
+        fn get(self: Self, folder: SpecialFolder) T {
+            inline for (std.meta.fields(Self)) |fld| {
+                if (self == @field(SpecialFolder, fld.name))
+                    return @field(self, fld.name);
+            }
+            unreachable;
+        }
+    };
+}
+
+/// Stores how to find each special folder on windows.
+const windows_folder_spec = comptime blk: {
+    @setEvalBranchQuota(10_000);
+    break :blk SpecialFolderConfig(WindowsFolderSpec){
+        .home = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{5E6C858F-0E22-4760-9AFE-EA3317B67173}") }, // FOLDERID_Profile
+        .documents = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{FDD39AD0-238F-46AF-ADB4-6C85480369C7}") }, // FOLDERID_Documents
+        .pictures = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{33E28130-4E1E-4676-835A-98395C3BC3BB}") }, // FOLDERID_Pictures
+        .music = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{4BD8D571-6D19-48D3-BE97-422220080E43}") }, // FOLDERID_Music
+        .videos = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{18989B1D-99B5-455B-841C-AB7C74E4DDFC}") }, // FOLDERID_Videos
+        .templates = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{A63293E8-664E-48DB-A079-DF759E0509F7}") }, // FOLDERID_Templates
+        .desktop = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{B4BFCC3A-DB2C-424C-B029-7FE99A87C641}") }, // FOLDERID_Desktop
+        .downloads = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{374DE290-123F-4565-9164-39C4925E467B}") }, // FOLDERID_Downloads
+        .public = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{DFDF76A2-C82A-4D63-906A-5644AC457385}") }, // FOLDERID_Public
+        .fonts = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{FD228CB7-AE11-4AE3-864C-16F3910AB8FE}") }, // FOLDERID_Fonts
+        .app_menu = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{625B53C3-AB48-4EC1-BA1F-A1EF4146FC19}") }, // FOLDERID_StartMenu
+        .cache = WindowsFolderSpec{ .by_env = .{ .root = "LOCALAPPDATA", .subdirs = &[_][]const u8{"Temp"} } }, // %LOCALAPPDATA%\Temp
+        .roaming_configuration = WindowsFolderSpec{ .by_env = .{ .root = "APPDATA", .subdirs = &[0][]const u8{} } }, // %APPDATA%
+        .local_configuration = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{F1B32785-6FBA-4FCF-9D55-7B8E7F157091}") }, // FOLDERID_LocalAppData
+        .data = WindowsFolderSpec{ .by_env = .{ .root = "APPDATA", .subdirs = &[0][]const u8{} } }, // %LOCALAPPDATA%\Temp
+        .system_folder = WindowsFolderSpec{ .by_guid = std.os.windows.GUID.parse("{1AC14E77-02E7-4E5D-B744-2EB1AE5198B7}") }, // FOLDERID_System
+        .runtime = WindowsFolderSpec{ .by_env = .{ .root = "LOCALAPPDATA", .subdirs = &[_][]const u8{"Temp"} } },
+    };
+};
+
+// Ref decls
+comptime {
+    _ = SpecialFolder;
+    _ = Error;
+    _ = open;
+    _ = getPath;
+}
+
+test "query each windows known folders" {
+    // TODO: Implement this test
+    _ = windows_folder_spec;
 }