Nim: Do not crash on empty nimprojects

Create a Nim Application using the wizard, remove main.nim, open.
Without this patch creator crashes.

Change-Id: Ia1628c67525e2fe9bb8dd9c76f62d7074844ccc4
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/nim/project/nimbuildconfigurationfactory.cpp

@@ -108,7 +108,9 @@ BuildConfiguration *NimBuildConfigurationFactory::create(Target *parent, const B
             break;
         }
         nimCompilerBuildStep->setDefaultCompilerOptions(defaultOption);
-        nimCompilerBuildStep->setTargetNimFile(project->nimFiles().first());
+        Utils::FileNameList nimFiles = project->nimFiles();
+        if (!nimFiles.isEmpty())
+            nimCompilerBuildStep->setTargetNimFile(nimFiles.first());
         buildSteps->appendStep(nimCompilerBuildStep);
     }
 

src/plugins/nim/project/nimcompilerbuildstep.cpp

@@ -26,6 +26,7 @@
 #include "nimcompilerbuildstep.h"
 #include "nimbuildconfiguration.h"
 #include "nimcompilerbuildstepconfigwidget.h"
+#include "nimproject.h"
 
 #include "../nimconstants.h"
 
@@ -50,6 +51,8 @@ NimCompilerBuildStep::NimCompilerBuildStep(BuildStepList *parentList)
             this, &NimCompilerBuildStep::updateProcessParameters);
     connect(this, &NimCompilerBuildStep::outFilePathChanged,
             bc, &NimBuildConfiguration::outFilePathChanged);
+    connect(bc->target()->project(), &ProjectExplorer::Project::fileListChanged,
+            this, &NimCompilerBuildStep::updateTargetNimFile);
     updateProcessParameters();
 }
 
@@ -202,5 +205,13 @@ void NimCompilerBuildStep::updateEnvironment()
     processParameters()->setEnvironment(bc->environment());
 }
 
+void NimCompilerBuildStep::updateTargetNimFile()
+{
+    if (!m_targetNimFile.isEmpty())
+        return;
+    const Utils::FileNameList nimFiles = static_cast<NimProject *>(project())->nimFiles();
+    if (!nimFiles.isEmpty())
+        setTargetNimFile(nimFiles.at(0));
 }
 
+} // namespace Nim

src/plugins/nim/project/nimcompilerbuildstep.h

@@ -74,6 +74,8 @@ private:
     void updateArguments();
     void updateEnvironment();
 
+    void updateTargetNimFile();
+
     DefaultBuildOptions m_defaultOptions;
     QStringList m_userCompilerOptions;
     Utils::FileName m_targetNimFile;