[libcalamares] Add isValid() to Settings

- settings can be invalid (missing data, whatever) and that
  can be used to shut things down early. Validity must be
  checked explicitly, though.

src/libcalamares/Settings.cpp

@@ -282,12 +282,6 @@ Settings::reconcileInstancesAndSequence()
     {
         for ( const auto& instanceKey : step.second )
         {
-            if ( !instanceKey.isValid() )
-            {
-                cWarning() << "Invalid instance key in *sequence*," << instanceKey;
-                continue;
-            }
-
             targetKey = instanceKey;
             const auto it = std::find_if( m_moduleInstances.constBegin(), m_moduleInstances.constEnd(), moduleFinder );
             if ( it == m_moduleInstances.constEnd() )
@@ -447,4 +441,25 @@ Settings::init( const QString& path )
     return new Calamares::Settings( path, true );
 }
 
+bool
+Settings::isValid() const
+{
+    if ( brandingComponentName().isEmpty() )
+    {
+        cWarning() << "No branding component is set";
+        return false;
+    }
+
+    const auto invalidDescriptor = []( const InstanceDescription& d ) { return !d.isValid(); };
+    const auto invalidDescriptorIt
+        = std::find_if( m_moduleInstances.constBegin(), m_moduleInstances.constEnd(), invalidDescriptor );
+    if ( invalidDescriptorIt != m_moduleInstances.constEnd() )
+    {
+        cWarning() << "Invalid module instance in *instances* or *sequence*";
+        return false;
+    }
+
+    return true;
+}
+
 }  // namespace Calamares

src/libcalamares/Settings.h

@@ -122,6 +122,13 @@ public:
 
     QString brandingComponentName() const;
 
+    /** @brief Are the settings consistent and valid?
+     *
+     * Checks that at least branding is set, and that the instances
+     * and sequence are valid.
+     */
+    bool isValid() const;
+
     /** @brief Is this a debugging run?
      *
      * Returns true if Calamares is in debug mode. In debug mode,

src/libcalamares/Tests.cpp

@@ -367,6 +367,7 @@ TestLibCalamares::testSettings()
     {
         Calamares::Settings s( false );
         QVERIFY( !s.debugMode() );
+        QVERIFY( !s.isValid() );
     }
     {
         Calamares::Settings s( true );
@@ -374,8 +375,10 @@ TestLibCalamares::testSettings()
         QVERIFY( s.moduleInstances().isEmpty() );
         QVERIFY( s.modulesSequence().isEmpty() );
         QVERIFY( s.brandingComponentName().isEmpty() );
+        QVERIFY( !s.isValid() );
 
         s.setConfiguration( R"(---
+branding: default  # needed for it to be considered valid
 instances:
     - module: welcome
       id: hi
@@ -397,7 +400,8 @@ sequence:
         QVERIFY( s.debugMode() );
         QCOMPARE( s.moduleInstances().count(), 4 );  // there are 4 module instances mentioned
         QCOMPARE( s.modulesSequence().count(), 2 );  // 2 steps (show, exec)
-        QVERIFY( s.brandingComponentName().isEmpty() );
+        QVERIFY( !s.brandingComponentName().isEmpty() );
+        QVERIFY( s.isValid() );
 
         // Make a lambda where we can adjust what it looks for from the outside,
         //   by capturing a reference.