Allow relative paths on non-existent directories

[tresf]

Switch SampleBuffer::tryToMakeRelative(...) to use cleanPath instead of canonicalFilePath.

canonicalFilePath has several limitations including:

1. Failure to handle a non-existant path (#4267)
2. Possible undesired symlink handling

[PhysSong]

Just a reminder, .replace( QDir::separator(), '/' ) can be removed when Qt4 support is completely dropped later.

[tresf]

Just a reminder, .replace( QDir::separator(), '/' ) can be removed when Qt4 support is completely dropped later.

Good to know... can you elaborate? Is the default behavior to use / in Qt5? If so where is this documented and is this across all Qt functions?

[PhysSong]

Documented in http://doc.qt.io/qt-5/qdir.html#cleanPath

[tresf]

Documented in http://doc.qt.io/qt-5/qdir.html#cleanPath

Yeah that doesn't have any "since qt5" warnings, so I just thought it was an example. Thanks for clarification.

[tresf]

For comparison:

4.8:

Removes all multiple directory separators "/" and resolves any "."s or ".."s found in the path, path.

5.x:

Returns path with directory separators normalized (converted to "/") and redundant ones removed, and "."s and ".."s resolved (as far as possible).

So I hope you understand my hesitation. :)

[tresf]

Hmm.... Here's the code for posterity...

static QString qt_cleanPath(const QString &path, bool *ok)
--
{
if (path.isEmpty())
return path;
QString name = path;
QChar dir_separator = QDir::separator();
if (dir_separator != QLatin1Char('/'))
name.replace(dir_separator, QLatin1Char('/'));
 
QString ret = qt_normalizePathSegments(name, OSSupportsUncPaths, ok);
 
// Strip away last slash except for root directories
if (ret.length() > 1 && ret.endsWith(QLatin1Char('/'))) {
#if defined (Q_OS_WIN)
#  if defined(Q_OS_WINRT)
if (!((ret.length() == 3 \|\| ret.length() == QDir::rootPath().length()) && ret.at(1) == QLatin1Char(':')))
#  else
if (!(ret.length() == 3 && ret.at(1) == QLatin1Char(':')))
#  endif
#endif
ret.chop(1);
}
 
return ret;
}

The only function that seems like it would touch \\ would be the qt_normalizePathSegments.cpp, but that specifically says in the source

// This method is shared with QUrl, so it doesn't deal with QDir::separator() ...

I guess I'll take your word for it. :)

[Wallacoloo]

@tresf it's about a third of the way down in that qt_cleanPath function:

name.replace(dir_separator, QLatin1Char('/'));

How do you feel about adding a short code comment explaining why we run .replace( QDir::separator(), '/' ) (maybe just linking to #4271 ) so that nobody else accidentally removes it, forgetting about Qt4 support?

[PhysSong]

Looking into Qt4's code, I found that even Qt 4.0 has the replacement logic. So we can safely remove that.

[tresf]

dir_separator, got it! Missed that one. Thanks!

So we can safely remove that.

Agreed. Will do.

[tresf]

I haven't actually tested any of this code myself (e.g for regressions to #4267). For starters, I was confused that QDir::cleanPath(...) actually returns a file path and not the parent folder. Fortunately the unit tests caught my mistake.

@PhysSong I'll let you merge this one since you're the bug submitter and the most likely to have tested this. :)

[tresf]

Seems like a lot of chatter over a string replacement, but this knowledge is only going to benefit the project for years to come. Thanks for the digging.

[PhysSong]

I found some more places where cleanPath can be used. Should I replace them in a separate PR?

[Wallacoloo]

@PhysSong Given this PR is from a tresf branch, I don't think you can easily add your own changes on top of this PR. I would say merge this one and then create a new PR for your changes.

[tresf]

Actually GitHub allows PRs to be modified now. It's a great feature especially for abandoned ones. we do it fairly often now. :)

[PhysSong]

What I'd like to do is using QDir::cleanPath to normalize data:/ search paths.

index 141085dd2..62bebff7c 100644
--- a/src/core/SampleBuffer.cpp
+++ b/src/core/SampleBuffer.cpp
@@ -1425,7 +1425,7 @@ QString SampleBuffer::tryToMakeRelative( const QString & file )
                // Iterate over all valid "data:/" searchPaths
                for ( const QString & path : QDir::searchPaths( "data" ) )
                {
-                       QString samplesPath = QString( path + samplesSuffix ).replace( QDir::separator(), '/' );
+                       QString samplesPath = QDir::cleanPath( path + samplesSuffix ) + "/";
                        if ( f.startsWith( samplesPath ) )
                        {
                                return QString( f ).mid( samplesPath.length() );

[tresf]

Not sure how well the data: portion is handled, but if it works, we can add it here.

[tresf]

I believe ensureTrailingSlash may be better here. The previous logic doesn't add any slashes.

[PhysSong]

Maybe, but don't have to be. QDir::cleanPath always strips trailing slash and previous logic always gives a path with trailing slash.
BTW, ensureTrailingSlash is defined in ConfigManager.cpp. If you want to use that function, you should move that into an header first.

[tresf]

Didn't know about trailing slash strip. That's nice. Looks good then. Merge?