eth, node: use APPDATA env to support cygwin/msys correctly

[hackmod]

since windows XP $APPDATA (%APPDATA%) is used.
Please see also

• http://environmentvariables.org/AppData
• https://www.askvg.com/list-of-environment-variables-in-windows-xp-vista-and-7/

for normal windows native environment, %HOME%(C:\Users\foobar) + \AppData\Roaming is correctly interpreted as %APPDATA%, but for cygwin/msys2 environment or powershell, %HOME% is /home/foobar/ and %HOME% + \AppData\Roaming is not %APPDATA% anymore.

Simply using %APPDATA% fix this issue.

[fjl]

Sorry for not following up with this last two weeks. I support this change, but fear that people will complain because geth doesn't find their old datadir anymore. Could you add a check to see whether there is a datadir at the old location? We already have backwards-compatibility checks like that for files inside datadir here.

While we're at it, there is an old issue about this: #2239. It says we shouldn't use AppData\Roaming because that might be located on a network drive.

[hackmod]

we can use %LOCALAPPDATA% env variable for AppData/Local, but %LOCALAPPDATA% env is only available above WIN Vista.

• for Ethash cache dir case - %LOCALAPPDATA% is more applicable.
• other %APPDATA% cases - since Win XP, %APPDATA% env is supported and using %APPDATA% is more reasonable but need to check previously saved data like as you already pointed out isOldGethResource related method. (or we can ignore for XP case)

[hackmod]

now, we can see %LOCALAPPDATA% is the right place for datadir.

how about this?

@@ -59,12 +62,28 @@ func DefaultDataDir() string {
                if runtime.GOOS == "darwin" {
                        return filepath.Join(home, "Library", "Ethereum")
                } else if runtime.GOOS == "windows" {
+                       dataDir := filepath.Join(home, "AppData", "Roaming", "Ethereum")
+                       if common.FileExist(filepath.Join(dataDir, "chaindata")) {
+                               log.Warn(fmt.Sprintf("XXX"))
+                               return dataDir
+                       }
                        appdata := os.Getenv("APPDATA")
                        if appdata != "" {
-                               return filepath.Join(appdata, "Ethereum")
+                               dataDir = filepath.Join(appdata, "Ethereum")
+                       } else {
+                               dataDir = filepath.Join(home, "AppData", "Roaming", "Ethereum")
+                       }
+                       if common.FileExist(filepath.Join(dataDir, "chaindata")) {
+                               log.Warn(fmt.Sprintf("XXX"))
+                               return dataDir
+                       }
+                       localappdata := os.Getenv("LOCALAPPDATA")
+                       if localappdata != "" {
+                               dataDir = filepath.Join(localappdata, "Ethereum")
                        } else {
-                               return filepath.Join(home, "AppData", "Roaming", "Ethereum")
+                               dataDir = filepath.Join(home, "AppData", "Local", "Ethereum")
                        }
+                       return dataDir
                } else {
                        return filepath.Join(home, ".ethereum")
                }

it looks somewhat ugly, but happy for old users and less issue for newcomers.

[holiman]

Changing this also involves Mist, which (at least historically) has sometimes interacted directly with the keystore folder (although I don't remember exactly under what circumstances, maybe during import). cc @evertonfraga what would happen if we move the keystore ?