Refine API for QgsProviderRegistry tests for preferred provider

for a URI to better handle ties, add direct method to determine
whether a particular provider should defer handling of a certain
URI to another (better equipped) provider

python/core/auto_generated/qgsproviderregistry.sip.in

@@ -281,20 +281,40 @@ Returns list of available providers by their keys
 Returns metadata of the provider or ``None`` if not found
 %End
 
-    QgsProviderMetadata *preferredProviderForUri( const QString &uri ) const;
+    QList< QgsProviderMetadata *> preferredProvidersForUri( const QString &uri ) const;
 %Docstring
-Returns the metadata for the preferred provider for opening the specified ``uri``.
+Returns the metadata for the preferred provider(s) for opening the specified ``uri``.
 
 The preferred provider is determined by comparing the priority returned by
 :py:func:`QgsProviderMetadata.priorityForUri()` for all registered providers, and selecting
 the provider with the largest non-zero priority.
 
-A ``None`` may be returned, which indicates that no providers are available which
+An empty list may be returned, which indicates that no providers are available which
 returned a non-zero priority for the specified URI.
 
 In the case that multiple providers returned the same priority for the URI then
-either of these providers will be returned. In this case the :py:func:`QgsProviderMetadata.priorityForUri()`
-implementation for the providers should be refined to avoid ties.
+all of these providers will be returned.
+
+.. seealso:: :py:func:`shouldDeferUriForOtherProviders`
+
+.. versionadded:: 3.18
+%End
+
+    bool shouldDeferUriForOtherProviders( const QString &uri, const QString &providerKey ) const;
+%Docstring
+Returns ``True`` if the provider with matching ``providerKey`` should defer handling of
+the specified ``uri`` to another provider.
+
+This method tests whether any providers are listed as the preferred provider for ``uri``
+(see :py:func:`~QgsProviderRegistry.preferredProvidersForUri`), and if so tests whether the specified provider is
+included in that preferred providers list. Returns ``True`` only if the specified provider
+is calculated as one of the preferred providers for the URI.
+
+In the case that there is no registered preferred provider for the URI then ``False`` will be
+returned, and the provider must use another metric to determine whether it should
+handle the URI.
+
+.. seealso:: :py:func:`preferredProvidersForUri`
 
 .. versionadded:: 3.18
 %End

src/core/qgsproviderregistry.cpp

@@ -746,18 +746,29 @@ QgsProviderMetadata *QgsProviderRegistry::providerMetadata( const QString &provi
   return findMetadata_( mProviders, providerKey );
 }
 
-QgsProviderMetadata *QgsProviderRegistry::preferredProviderForUri( const QString &uri ) const
+QList< QgsProviderMetadata * > QgsProviderRegistry::preferredProvidersForUri( const QString &uri ) const
 {
-  QgsProviderMetadata *res = nullptr;
+  QList< QgsProviderMetadata * > res;
   int maxPriority = 0;
   for ( auto it = mProviders.begin(); it != mProviders.end(); ++it )
   {
     const int thisProviderPriority = it->second->priorityForUri( uri );
     if ( thisProviderPriority > maxPriority )
     {
+      res.clear();
       maxPriority = thisProviderPriority;
-      res = it->second;
     }
+    if ( thisProviderPriority == maxPriority )
+      res.append( it->second );
   }
   return res;
 }
+
+bool QgsProviderRegistry::shouldDeferUriForOtherProviders( const QString &uri, const QString &providerKey ) const
+{
+  const QList< QgsProviderMetadata * > providers = preferredProvidersForUri( uri );
+  if ( providers.empty() )
+    return false;
+
+  return !providers.contains( QgsProviderRegistry::instance()->providerMetadata( providerKey ) );
+}

src/core/qgsproviderregistry.h

@@ -283,22 +283,40 @@ class CORE_EXPORT QgsProviderRegistry
     QgsProviderMetadata *providerMetadata( const QString &providerKey ) const;
 
     /**
-     * Returns the metadata for the preferred provider for opening the specified \a uri.
+     * Returns the metadata for the preferred provider(s) for opening the specified \a uri.
      *
      * The preferred provider is determined by comparing the priority returned by
      * QgsProviderMetadata::priorityForUri() for all registered providers, and selecting
      * the provider with the largest non-zero priority.
      *
-     * A NULLPTR may be returned, which indicates that no providers are available which
+     * An empty list may be returned, which indicates that no providers are available which
      * returned a non-zero priority for the specified URI.
      *
      * In the case that multiple providers returned the same priority for the URI then
-     * either of these providers will be returned. In this case the QgsProviderMetadata::priorityForUri()
-     * implementation for the providers should be refined to avoid ties.
+     * all of these providers will be returned.
      *
+     * \see shouldDeferUriForOtherProviders()
      * \since QGIS 3.18
      */
-    QgsProviderMetadata *preferredProviderForUri( const QString &uri ) const;
+    QList< QgsProviderMetadata *> preferredProvidersForUri( const QString &uri ) const;
+
+    /**
+     * Returns TRUE if the provider with matching \a providerKey should defer handling of
+     * the specified \a uri to another provider.
+     *
+     * This method tests whether any providers are listed as the preferred provider for \a uri
+     * (see preferredProvidersForUri()), and if so tests whether the specified provider is
+     * included in that preferred providers list. Returns TRUE only if the specified provider
+     * is calculated as one of the preferred providers for the URI.
+     *
+     * In the case that there is no registered preferred provider for the URI then FALSE will be
+     * returned, and the provider must use another metric to determine whether it should
+     * handle the URI.
+     *
+     * \see preferredProvidersForUri()
+     * \since QGIS 3.18
+     */
+    bool shouldDeferUriForOtherProviders( const QString &uri, const QString &providerKey ) const;
 
     /**
      * Returns a file filter string for supported vector files.

tests/src/providers/testqgseptprovider.cpp

@@ -112,8 +112,11 @@ void TestQgsEptProvider::decodeUri()
 void TestQgsEptProvider::preferredUri()
 {
   // test that EPT is the preferred provider for ept.json uris
-  QCOMPARE( QgsProviderRegistry::instance()->preferredProviderForUri( QStringLiteral( "/home/test/ept.json" ) )->key(), QStringLiteral( "ept" ) );
-  QCOMPARE( QgsProviderRegistry::instance()->preferredProviderForUri( QStringLiteral( "/home/test/EPT.JSON" ) )->key(), QStringLiteral( "ept" ) );
+  QCOMPARE( QgsProviderRegistry::instance()->preferredProvidersForUri( QStringLiteral( "/home/test/ept.json" ) ), QList< QgsProviderMetadata * >() << QgsProviderRegistry::instance()->providerMetadata( QStringLiteral( "ept" ) ) );
+  QCOMPARE( QgsProviderRegistry::instance()->preferredProvidersForUri( QStringLiteral( "/home/test/EPT.JSON" ) ), QList< QgsProviderMetadata * >() << QgsProviderRegistry::instance()->providerMetadata( QStringLiteral( "ept" ) ) );
+
+  QVERIFY( !QgsProviderRegistry::instance()->shouldDeferUriForOtherProviders( QStringLiteral( "/home/test/ept.json" ), QStringLiteral( "ept" ) ) );
+  QVERIFY( QgsProviderRegistry::instance()->shouldDeferUriForOtherProviders( QStringLiteral( "/home/test/ept.json" ), QStringLiteral( "ogr" ) ) );
 }
 
 

tests/src/python/test_qgsproviderregistry.py

@@ -61,6 +61,11 @@ def testCreateProvider(self):
 
         self.assertIsNone(QgsProviderRegistry.instance().createProvider('asdasdasdasdasd', ''))
 
+    def testShouldDeferUriForOtherProviders(self):
+        self.assertTrue(QgsProviderRegistry.instance().shouldDeferUriForOtherProviders('/home/nyall/ept.json', 'ogr'))
+        self.assertFalse(QgsProviderRegistry.instance().shouldDeferUriForOtherProviders('/home/nyall/ept.json', 'ept'))
+        self.assertFalse(QgsProviderRegistry.instance().shouldDeferUriForOtherProviders('/home/nyall/my.json', 'ogr'))
+
 
 if __name__ == '__main__':
     unittest.main()