Merge bitcoin/bitcoin#27064: system: use %LOCALAPPDATA% as default datadir on windows

84900ac doc: add release-notes-27064.md (Matthew Zipkin)
855dd8d system: use %LOCALAPPDATA% as default datadir on windows (Matthew Zipkin)

Pull request description:

  Closes bitcoin/bitcoin#2391

  This PR changes the default datadir location on Windows from `C:\Users\Username\AppData\Roaming\Bitcoin` to `C:\Users\Username\AppData\Local\Bitcoin`. This change only applies to fresh installs. To preserve backwards compatibility, on startup we check for the existence of `C:\Users\Username\AppData\Roaming\Bitcoin\chainstate` and if it is there, we continue using the "Roaming" directory as the default datadir location.

  [Note that in Windows 11 this change may be moot:](https://learn.microsoft.com/en-us/uwp/api/windows.storage.applicationdata.roamingfolder?view=winrt-22621)

  > Roaming data and settings is no longer supported as of Windows 11. The recommended replacement is [Azure App Service](https://learn.microsoft.com/en-us/azure/app-service/). Azure App Service is widely supported, well documented, reliable, and supports cross-platform/cross-ecosystem scenarios such as iOS, Android and web. Settings stored here no longer roam (as of Windows 11), but the settings store is still available.

ACKs for top commit:
  achow101:
    ACK 84900ac
  BenWestgate:
    crACK bitcoin/bitcoin@84900ac
  hebasto:
    re-ACK 84900ac, only addressed feedback since my recent [review](bitcoin/bitcoin#27064 (review)).

Tree-SHA512: 807c6e89571287e2c8f4934229aec91ef28e7d0a675234acf1b7d085c24c7b73a08b6e345fbfc9038e6239187b6b69c08490ddaa1c057de5ea975c4a000bba42

Author: achow101

doc/bitcoin-conf.md

@@ -59,7 +59,7 @@ The `includeconf=<file>` option in the `bitcoin.conf` file can be used to includ
 
 Operating System | Data Directory | Example Path
 -- | -- | --
-Windows | `%APPDATA%\Bitcoin\` | `C:\Users\username\AppData\Roaming\Bitcoin\bitcoin.conf`
+Windows | `%LOCALAPPDATA%\Bitcoin\` | `C:\Users\username\AppData\Local\Bitcoin\bitcoin.conf`
 Linux | `$HOME/.bitcoin/` | `/home/username/.bitcoin/bitcoin.conf`
 macOS | `$HOME/Library/Application Support/Bitcoin/` | `/Users/username/Library/Application Support/Bitcoin/bitcoin.conf`
 

doc/files.md

@@ -28,7 +28,7 @@ Platform | Data directory path
 ---------|--------------------
 Linux    | `$HOME/.bitcoin/`
 macOS    | `$HOME/Library/Application Support/Bitcoin/`
-Windows  | `%APPDATA%\Bitcoin\` <sup>[\[1\]](#note1)</sup>
+Windows  | `%LOCALAPPDATA%\Bitcoin\` <sup>[\[1\]](#note1)</sup>
 
 2. A custom data directory path can be specified with the `-datadir` option.
 

doc/managing-wallets.md

@@ -20,7 +20,7 @@ By default, wallets are created in the `wallets` folder of the data directory, w
 | Operating System | Default wallet directory                                    |
 | -----------------|:------------------------------------------------------------|
 | Linux            | `/home/<user>/.bitcoin/wallets`                             |
-| Windows          | `C:\Users\<user>\AppData\Roaming\Bitcoin\wallets`           |
+| Windows          | `C:\Users\<user>\AppData\Local\Bitcoin\wallets`             |
 | macOS            | `/Users/<user>/Library/Application Support/Bitcoin/wallets` |
 
 ### 1.2 Encrypting the Wallet

doc/release-notes/release-notes-27064.md

@@ -0,0 +1,7 @@
+Files
+-----
+
+The default data directory on Windows has been moved from `C:\Users\Username\AppData\Roaming\Bitcoin`
+to `C:\Users\Username\AppData\Local\Bitcoin`. Bitcoin Core will check the existence
+of the old directory first and continue to use that directory for backwards
+compatibility if it is present.

src/common/args.cpp

@@ -696,12 +696,19 @@ bool HasTestOption(const ArgsManager& args, const std::string& test_option)
 
 fs::path GetDefaultDataDir()
 {
-    // Windows: C:\Users\Username\AppData\Roaming\Bitcoin
+    // Windows:
+    //   old: C:\Users\Username\AppData\Roaming\Bitcoin
+    //   new: C:\Users\Username\AppData\Local\Bitcoin
     // macOS: ~/Library/Application Support/Bitcoin
     // Unix-like: ~/.bitcoin
 #ifdef WIN32
     // Windows
-    return GetSpecialFolderPath(CSIDL_APPDATA) / "Bitcoin";
+    // Check for existence of datadir in old location and keep it there
+    fs::path legacy_path = GetSpecialFolderPath(CSIDL_APPDATA) / "Bitcoin";
+    if (fs::exists(legacy_path)) return legacy_path;
+
+    // Otherwise, fresh installs can start in the new, "proper" location
+    return GetSpecialFolderPath(CSIDL_LOCAL_APPDATA) / "Bitcoin";
 #else
     fs::path pathRet;
     char* pszHome = getenv("HOME");