Split shapefile CPG/LDID based encoding detection to separate methods

src/core/qgsogrutils.cpp

@@ -750,6 +750,15 @@ QgsCoordinateReferenceSystem QgsOgrUtils::OGRSpatialReferenceToCrs( OGRSpatialRe
 }
 
 QString QgsOgrUtils::readShapefileEncoding( const QString &path )
+{
+  const QString cpgEncoding = readShapefileEncodingFromCpg( path );
+  if ( !cpgEncoding.isEmpty() )
+    return cpgEncoding;
+
+  return readShapefileEncodingFromLdid( path );
+}
+
+QString QgsOgrUtils::readShapefileEncodingFromCpg( const QString &path )
 {
   // unfortunately OGR's routines for calculating the shapefile encoding aren't exposed anywhere in the GDAL c api, so
   // re-implement them here...
@@ -798,6 +807,24 @@ QString QgsOgrUtils::readShapefileEncoding( const QString &path )
     }
   }
 
+  return QString();
+}
+
+QString QgsOgrUtils::readShapefileEncodingFromLdid( const QString &path )
+{
+  // unfortunately OGR's routines for calculating the shapefile encoding aren't exposed anywhere in the GDAL c api, so
+  // re-implement them here...
+
+  // from OGRShapeLayer::ConvertCodePage
+  // https://github.com/OSGeo/gdal/blob/master/gdal/ogr/ogrsf_frmts/shape/ogrshapelayer.cpp#L342
+
+  if ( !QFileInfo::exists( path ) )
+    return QString();
+
+  // first try to read cpg file, if present
+  const QFileInfo fi( path );
+  const QString baseName = fi.completeBaseName();
+
   // fallback to LDID value, read from DBF file
   const QString dbfPath = fi.dir().filePath( QStringLiteral( "%1.%2" ).arg( baseName, fi.suffix() == QLatin1String( "SHP" ) ? QStringLiteral( "DBF" ) : QStringLiteral( "dbf" ) ) );
   if ( QFile::exists( dbfPath ) )

src/core/qgsogrutils.h

@@ -290,9 +290,36 @@ class CORE_EXPORT QgsOgrUtils
      * Reads the encoding of the shapefile at the specified \a path (where \a path is the
      * location of the ".shp" file).
      *
+     * This method considers both the CPG specified encoding and the DBF LDID encoding
+     * (priority goes to CPG based encoding)
+     *
+     * \see readShapefileEncodingFromCpg()
+     * \see readShapefileEncodingFromLdid()
      * \since QGIS 3.12
      */
     static QString readShapefileEncoding( const QString &path );
+
+    /**
+     * Reads the encoding of the shapefile at the specified \a path (where \a path is the
+     * location of the ".shp" file), from the CPG specified encoding.
+     *
+     * Return an empty string if CPG based encoding was not found.
+     *
+     * \see readShapefileEncoding()
+     * \since QGIS 3.12
+     */
+    static QString readShapefileEncodingFromCpg( const QString &path );
+
+    /**
+     * Reads the encoding of the shapefile at the specified \a path (where \a path is the
+     * location of the ".shp" file), from the DBF LDID encoding.
+     *
+     * Return an empty string if LDID based encoding was not found.
+     *
+     * \see readShapefileEncoding()
+     * \since QGIS 3.12
+     */
+    static QString readShapefileEncodingFromLdid( const QString &path );
 };
 
 #endif // QGSOGRUTILS_H