InnoSetup: don't uninstall changed files - inno-setup

Question

How to tell InnoSetup to not uninstall (text) files which had been changed by the user (== are different from those installed by InnoSetup)?
Or maybe more difficult: when installing a new version over an existing, InnoSetup should ask the user whether to overwrite the changed file, but on a pure uninstall, it should uninstall it without asking.

Answer 1

I recently had a similar problem. This was my solution to detect if a text file (profile) has been changed from the one installed during the last installation run:
Use ISPP (Inno Setup Pre-Processor) to create the list of text files and their hashes at compile time:
[Files]
; ...
#define FindHandle
#define FindResult
#define Mask "Profiles\*.ini"
#sub ProcessFoundFile
#define FileName "Profiles\" + FindGetFileName(FindHandle)
#define FileMd5 GetMd5OfFile(FileName)
Source: {#FileName}; DestDir: {app}\Profiles; Components: profiles; \
Check: ProfileCheck('{#FileMd5}'); AfterInstall: ProfileAfterInstall('{#FileMd5}');
#endsub
#for {FindHandle = FindResult = FindFirst(Mask, 0); FindResult; FindResult = FindNext(FindHandle)} ProcessFoundFile
At the top of the "Code" section I define some useful things:
[Code]
var
PreviousDataCache : tStringList;
function InitializeSetup() : boolean;
begin
// Initialize global variable
PreviousDataCache := tStringList.Create();
result := TRUE;
end;
function BoolToStr( Value : boolean ) : string;
begin
if ( not Value ) then
result := 'false'
else
result := 'true';
end;
In the "Check" event handler I compare the hashes of previous install and current file:
function ProfileCheck( FileMd5 : string ) : boolean;
var
TargetFileName, TargetFileMd5, PreviousFileMd5 : string;
r : integer;
begin
result := FALSE;
TargetFileName := ExpandConstant(CurrentFileName());
Log('Running check procedure for file: ' + TargetFileName);
if not FileExists(TargetFileName) then
begin
Log('Check result: Target file does not exist yet.');
result := TRUE;
exit;
end;
try
TargetFileMd5 := GetMd5OfFile(TargetFileName);
except
TargetFileMd5 := '(error)';
end;
if ( CompareText(TargetFileMd5, FileMd5) = 0 ) then
begin
Log('Check result: Target matches file from setup.');
result := TRUE;
exit;
end;
PreviousFileMd5 := GetPreviousData(ExtractFileName(TargetFileName), '');
if ( PreviousFileMd5 = '' ) then
begin
r := MsgBox(TargetFileName + #10#10 +
'The existing file is different from the one Setup is trying to install. ' +
'It is recommended that you keep the existing file.' + #10#10 +
'Do you want to keep the existing file?', mbConfirmation, MB_YESNO);
result := (r = idNo);
Log('Check result: ' + BoolToStr(result));
end
else if ( CompareText(PreviousFileMd5, TargetFileMd5) <> 0 ) then
begin
r := MsgBox(TargetFileName + #10#10 +
'The existing file has been modified since the last run of Setup. ' +
'It is recommended that you keep the existing file.' + #10#10 +
'Do you want to keep the existing file?', mbConfirmation, MB_YESNO);
result := (r = idNo);
Log('Check result: ' + BoolToStr(result));
end
else
begin
Log('Check result: Existing target has no local modifications.');
result := TRUE;
end;
end;
In the "AfterInstall" event handler I mark the file hash to be stored in
Registry later. Because in my tests the event was triggered even if the file move failed (target file is read-only) I compare the hash again to find out if the file move was successful:
procedure ProfileAfterInstall( FileMd5 : string );
var
TargetFileName, TargetFileMd5 : string;
begin
TargetFileName := ExpandConstant(CurrentFileName());
try
TargetFileMd5 := GetMd5OfFile(TargetFileName);
except
TargetFileMd5 := '(error)';
end;
if ( CompareText(TargetFileMd5, FileMd5) = 0 ) then
begin
Log('Storing hash of installed file: ' + TargetFileName);
PreviousDataCache.Add(ExtractFileName(TargetFileName) + '=' + FileMd5);
end;
end;
procedure RegisterPreviousData( PreviousDataKey : integer );
var
Name, Value : string;
i, n : integer;
begin
for i := 0 to PreviousDataCache.Count-1 do
begin
Value := PreviousDataCache.Strings[i];
n := Pos('=', Value);
if ( n > 0 ) then
begin
Name := Copy(Value, 1, n-1);
Value := Copy(Value, n+1, MaxInt);
SetPreviousData(PreviousDataKey, Name, Value);
end;
end;
end;

Answer 2

Inno can't do this check natively.
To not replace changed files during install, you'll need to use custom [Code] to do a checksum and compare against a known good value that is precomputed or saved from the previous install.
To avoid removing them during uninstall, you'll need to disable Inno's own uninstall for that file and check against the same checksum before removing them, again in [Code].
Note that it's better to keep any files the user can edit outside of the setup to handle this situation better and to correctly adhere to the application guidelines.