[patch] improve error output

[Georg Baum]

The investigation of bug 9139 showed that the error message we give when a 
file operation fails is not too clever. The attached patch improves this. It 
is still not optimal (since qt has a very limited set of error causes that 
are reported), but if we want to get the real error from the OS we have to 
implement it in a platform specific way.

In my experience error messages that are as exact as possible help a lot 
when investigating bug reports: You need to ask less questions, since the 
bug report itself will contain more information. OK to go in?

Georg
diff --git a/src/support/FileName.cpp b/src/support/FileName.cpp
index 9506666..3423972 100644
--- a/src/support/FileName.cpp
+++ b/src/support/FileName.cpp
@@ -238,10 +238,17 @@ bool FileName::copyTo(FileName const & name, bool keepsymlink,
 		return copyTo(target, true);
 	}
 	QFile::remove(name.d->fi.absoluteFilePath());
-	bool success = QFile::copy(d->fi.absoluteFilePath(), name.d->fi.absoluteFilePath());
-	if (!success)
-		LYXERR0("FileName::copyTo(): Could not copy file "
-			<< *this << " to " << name);
+	QFile f(d->fi.absoluteFilePath());
+	bool const success = f.copy(name.d->fi.absoluteFilePath());
+	if (!success) {
+		QString const error(f.errorString());
+		if (error.isEmpty())
+			LYXERR0("FileName::copyTo(): Could not copy file "
+				<< *this << " to " << name);
+		else
+			LYXERR0("FileName::copyTo(): Could not copy file "
+				<< *this << " to " << name << ": " << fromqstr(error));
+	}
 	return success;
 }
 
@@ -249,9 +256,16 @@ bool FileName::copyTo(FileName const & name, bool keepsymlink,
 bool FileName::renameTo(FileName const & name) const
 {
 	LYXERR(Debug::FILES, "Renaming " << name << " as " << *this);
-	bool success = QFile::rename(d->fi.absoluteFilePath(), name.d->fi.absoluteFilePath());
-	if (!success)
-		LYXERR0("Could not rename file " << *this << " to " << name);
+	QFile f(d->fi.absoluteFilePath());
+	bool const success = f.rename( name.d->fi.absoluteFilePath());
+	if (!success) {
+		QString const error(f.errorString());
+		if (error.isEmpty())
+			LYXERR0("Could not rename file " << *this << " to " << name);
+		else
+			LYXERR0("Could not rename file " << *this << " to "
+				<< name << ": " << fromqstr(error));
+	}
 	return success;
 }
 
@@ -261,10 +275,16 @@ bool FileName::moveTo(FileName const & name) const
 	LYXERR(Debug::FILES, "Moving " << name << " to " << *this);
 	QFile::remove(name.d->fi.absoluteFilePath());
 
-	bool success = QFile::rename(d->fi.absoluteFilePath(),
-		name.d->fi.absoluteFilePath());
-	if (!success)
-		LYXERR0("Could not move file " << *this << " to " << name);
+	QFile f(d->fi.absoluteFilePath());
+	bool const success = f.rename(name.d->fi.absoluteFilePath());
+	if (!success) {
+		QString const error(f.errorString());
+		if (error.isEmpty())
+			LYXERR0("Could not move file " << *this << " to " << name);
+		else
+			LYXERR0("Could not move file " << *this << " to "
+				<< name << ": " << fromqstr(error));
+	}
 	return success;
 }