libipa: awb: Fix non-virtual destructor warning in AwbStats

The AwbStats structure has virtual functions but a publicly accessible
non-virtual destructors. This can cause undefined behaviour if deleting
a derived class instance through a pointer to the base AwbStats class.

The problem is theoretical only as no code in libcamera is expected to
perform such deletion, but compilers can't know that and will emit a
warning if the -Wnon-virtual-dtor option is enabled.

Fixing this can be done by declaring a virtual public destructor in the
AwbStats class. A more efficient alternative is to declare a protected
non-virtual destructor, ensuring that instances can't be deleted through
a pointer to the base class. Do so, and mark the derived RkISP1AwbStats
as final to avoid the same warning.

Fixes: 6f663990a0 ("libipa: Add AWB algorithm base class")
Reported-by: Milan Zamazal <mzamazal@redhat.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>
Tested-by: Milan Zamazal <mzamazal@redhat.com>

src/ipa/libipa/awb.h

@@ -27,6 +27,9 @@ struct AwbResult {
 struct AwbStats {
 	virtual double computeColourError(const RGB<double> &gains) const = 0;
 	virtual RGB<double> rgbMeans() const = 0;
+
+protected:
+	~AwbStats() = default;
 };
 
 class AwbAlgorithm

src/ipa/rkisp1/algorithms/awb.cpp

@@ -42,7 +42,7 @@ constexpr int32_t kDefaultColourTemperature = 5000;
 /* Minimum mean value below which AWB can't operate. */
 constexpr double kMeanMinThreshold = 2.0;
 
-class RkISP1AwbStats : public AwbStats
+class RkISP1AwbStats final : public AwbStats
 {
 public:
 	RkISP1AwbStats(const RGB<double> &rgbMeans)