(Suggest to) uninstall previous versions

Author: chyndman

ElixirWeb.iss

@@ -90,6 +90,7 @@ Filename: "{tmp}\ISCC.exe"; Parameters: "/dSkipWelcome /dNoCompression Elixir.is
 Filename: "{tmp}\Output\elixir-v{#StrInspectScriptConst('CacheSelectedRelease.Version')}-setup.exe"; Flags: nowait; StatusMsg: "Starting Elixir installer..."
 
 [Tasks]
+Name: "unins_previous"; Description: "Uninstall previous version at {#StrInspectScriptConst('GetPreviousAppPath')} (Recommended)"; Check: CheckPreviousVersionExists
 Name: "erlang"; Description: "Install Erlang"; Check: CheckToInstallErlang
 Name: "erlang\32"; Description: "{#StrInspectScriptConst('GlobalErlangData.Name32')}"; Flags: exclusive
 Name: "erlang\64"; Description: "{#StrInspectScriptConst('GlobalErlangData.Name64')}"; Flags: exclusive; Check: IsWin64
@@ -103,6 +104,7 @@ Name: "existingpath"; Description: "Append {#StrInspectScriptConst('GetLatestErl
 #include "src\elixir_lookup.iss"
 #include "src\erlang_data.iss"
 #include "src\erlang_env.iss"
+#include "src\unins_previous.iss"
 
 var
   GlobalPageSelRelease: TInputOptionWizardPage;
@@ -129,10 +131,14 @@ end;
 procedure CurPageChanged(CurPageID: Integer);
 var
   ListBoxesToCheck: array[0..1] of TNewCheckListBox;
+  _int: Integer;
 begin
   if CurPageID = wpPreparing then begin
     // We're on the page after the "Ready To Install" page but before [Files] and [Run] are processed
     
+    if IsTaskSelected('unins_previous') then
+      ExecAsOriginalUser(GetPreviousUninsExe, '/SILENT', '', SW_SHOW, ewWaitUntilTerminated, _int);
+
     with GlobalErlangData do begin
       if IsTaskSelected('erlang\32') then
         // 32-bit OTP needs to be downloaded before it's installed

src/unins_previous.iss

@@ -0,0 +1,43 @@
+// unins_previous.iss - Functionality to check for previous Elixir installations
+// Copyright 2014 Chris Hyndman
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//       http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+
+[Code]
+
+function GetPreviousUninsExe: String;
+var
+  UninsPath: String;
+begin
+  UninsPath := '';
+  Result := '';
+  if RegQueryStringValue(HKLM, 'SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\Elixir_is1', 'UninstallString', UninsPath) then begin
+    Result := RemoveQuotes(UninsPath);
+  end else if RegQueryStringValue(HKLM, 'SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Elixir_is1', 'UninstallString', UninsPath) then begin
+    Result := RemoveQuotes(UninsPath);
+  end else if RegQueryStringValue(HKCU, 'Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\Elixir_is1', 'UninstallString', UninsPath) then begin
+    Result := RemoveQuotes(UninsPath); 
+  end else if RegQueryStringValue(HKCU, 'Software\Microsoft\Windows\CurrentVersion\Uninstall\Elixir_is1', 'UninstallString', UninsPath) then begin
+    Result := RemoveQuotes(UninsPath);
+  end;  
+end;
+
+function GetPreviousAppPath: String;
+begin
+  Result := RemoveBackslashUnlessRoot(ExtractFilePath(GetPreviousUninsExe));
+end;
+
+function CheckPreviousVersionExists: Boolean;
+begin
+  Result := (GetPreviousUninsExe <> '');
+end;