SL-10077: Save correct uninstall directory and (un)install mode.

Curiously, the value of $INSTDIR is correct before MULTIUSER_UNINIT, but is
made incorrect by MULTIUSER_UNINIT. Save and restore the correct value.

Saving $MultiUser.InstallMode in the registry (by setting relevant macros
examined by MultiUser.nsh) is susceptible to overwriting if the user installs
multiple viewers with the same channel name. Instead, write an InstallMode.txt
in the install directory, and read it back on uninstall. Of course, add it to
the files to be deleted on uninstall.

indra/newview/installers/windows/installer_template.nsi

@@ -117,9 +117,12 @@ AutoCloseWindow true					# After all files install, close window
 # should make MultiUser.nsh initialization read existing INSTDIR from registry
 !define MULTIUSER_INSTALLMODE_INSTDIR_REGISTRY_KEY "${INSTNAME_KEY}"
 !define MULTIUSER_INSTALLMODE_INSTDIR_REGISTRY_VALUENAME ""
-# should make MultiUser.nsh initialization write $MultiUser.InstallMode to registry
-!define MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_KEY "${INSTNAME_KEY}"
-!define MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_VALUENAME "InstallMode"
+# Don't set MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_KEY and
+# MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_VALUENAME to cause the installer to
+# write $MultiUser.InstallMode to the registry, because when the user installs
+# multiple viewers with the same channel (same ${INSTNAME}, hence same
+# ${INSTNAME_KEY}), the registry entry is overwritten. Instead we'll write a
+# little file into the install directory -- see .onInstSuccess and un.onInit.
 !include MultiUser.nsh
 !include MUI2.nsh
 !define MUI_BGCOLOR FFFFFF
@@ -239,7 +242,21 @@ FunctionEnd
 ;; Prep Uninstaller Section
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 Function un.onInit
-!insertmacro MULTIUSER_UNINIT
+    # Save $INSTDIR -- it appears to have the correct value before
+    # MULTIUSER_UNINIT, but then gets munged by MULTIUSER_UNINIT?!
+    Push $INSTDIR
+    !insertmacro MULTIUSER_UNINIT
+    Pop $INSTDIR
+
+    # Now read InstallMode.txt from $INSTDIR
+    Push $0
+    ClearErrors
+    FileOpen $0 "$INSTDIR\InstallMode.txt" r
+    IfErrors skipread
+    FileRead $0 $MultiUser.InstallMode
+    FileClose $0
+skipread:
+    Pop $0
 
 %%ENGAGEREGISTRY%%
 
@@ -248,10 +265,10 @@ Function un.onInit
     IfErrors lbl_end
 	StrCpy $LANGUAGE $0
 lbl_end:
-    Return
 
-    # Does MultiUser.nsh init read back
-    # MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_KEY into $MultiUser.InstallMode?
+##  MessageBox MB_OK "After restoring:$\n$$INSTDIR = '$INSTDIR'$\n$$MultiUser.InstallMode = '$MultiUser.InstallMode'$\n$$LANGUAGE = '$LANGUAGE'"
+
+    Return
 
 FunctionEnd
 
@@ -417,8 +434,10 @@ StrCpy $INSTSHORTCUT "${SHORTCUT}"
 # MULTIUSER_INSTALLMODE_DEFAULT_REGISTRY_VALUENAME
 # Couln't get NSIS to expand $MultiUser.InstallMode into the function name at Call time
 ${If} $MultiUser.InstallMode == 'AllUsers'
+##MessageBox MB_OK "Uninstalling for all users"
   Call un.MultiUser.InstallMode.AllUsers
 ${Else}
+##MessageBox MB_OK "Uninstalling for current user"
   Call un.MultiUser.InstallMode.CurrentUser
 ${EndIf}
 
@@ -626,6 +645,9 @@ Function un.ProgramFiles
 # This placeholder is replaced by the complete list of files to uninstall by viewer_manifest.py
 %%DELETE_FILES%%
 
+# our InstallMode.txt
+Delete "$INSTDIR\InstallMode.txt"
+
 # Optional/obsolete files.  Delete won't fail if they don't exist.
 Delete "$INSTDIR\autorun.bat"
 Delete "$INSTDIR\dronesettings.ini"
@@ -675,7 +697,13 @@ FunctionEnd
 ;; After install completes, launch app
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 Function .onInstSuccess
-        Call CheckWindowsServPack		# Warn if not on the latest SP before asking to launch.
+        Push $0
+        FileOpen $0 "$INSTDIR\InstallMode.txt" w
+        # No newline -- this is for our use, not for users to read.
+        FileWrite $0 "$MultiUser.InstallMode"
+        FileClose $0
+        Pop $0
+
         Push $R0
         Push $0
         ;; MAINT-7812: Only write nsis.winstall file with /marker switch
@@ -694,7 +722,8 @@ Function .onInstSuccess
         ClearErrors
         Pop $0
         Pop $R0
-        Push $R0					# Option value, unused# 
+
+        Call CheckWindowsServPack		# Warn if not on the latest SP before asking to launch.
         StrCmp $SKIP_AUTORUN "true" +2;
         # Assumes SetOutPath $INSTDIR
         # Run INSTEXE (our updater), passing VIEWER_EXE plus the command-line
@@ -711,7 +740,6 @@ Function .onInstSuccess
         # must be a distinct command-line token, but DO NOT quote the language
         # string because it must decompose into separate command-line tokens.
         Exec '"$INSTDIR\$INSTEXE" precheck "$INSTDIR\$VIEWER_EXE" $SHORTCUT_LANG_PARAM'
-        Pop $R0
 # 
 FunctionEnd