presets: Convert allowNoFiles to enum class

This improves readability at the call site when "yes" is desired.

Source/QtDialog/QCMake.cxx

@@ -541,7 +541,8 @@ void QCMake::setUpEnvironment() const
 void QCMake::loadPresets()
 {
   auto result = this->CMakePresetsGraph.ReadProjectPresets(
-    this->SourceDirectory.toStdString(), true);
+    this->SourceDirectory.toStdString(),
+    cmCMakePresetsGraph::ReadOption::AllowNoFiles);
   if (!result) {
     emit this->presetLoadError(
       this->SourceDirectory,

Source/cmCMakePresetsGraph.cxx

@@ -1142,12 +1142,12 @@ std::string cmCMakePresetsGraph::GetUserFilename(std::string const& sourceDir)
 }
 
 bool cmCMakePresetsGraph::ReadProjectPresets(std::string const& sourceDir,
-                                             bool allowNoFiles)
+                                             ReadOption readFilesOption)
 {
   this->SourceDir = cmSystemTools::CollapseFullPath(sourceDir);
   this->ClearPresets();
 
-  if (!this->ReadProjectPresetsInternal(allowNoFiles)) {
+  if (!this->ReadProjectPresetsInternal(readFilesOption)) {
     this->ClearPresets();
     return false;
   }
@@ -1183,7 +1183,8 @@ std::string cmCMakePresetsGraph::GetGeneratorForPreset(
   return {};
 }
 
-bool cmCMakePresetsGraph::ReadProjectPresetsInternal(bool allowNoFiles)
+bool cmCMakePresetsGraph::ReadProjectPresetsInternal(
+  ReadOption readFilesOption)
 {
   bool haveOneFile = false;
 
@@ -1209,7 +1210,7 @@ bool cmCMakePresetsGraph::ReadProjectPresetsInternal(bool allowNoFiles)
   assert(inProgressFiles.empty());
 
   if (!haveOneFile) {
-    if (allowNoFiles) {
+    if (readFilesOption == ReadOption::AllowNoFiles) {
       return true;
     }
     cmCMakePresetsErrors::FILE_NOT_FOUND(filename, &this->parseState);

Source/cmCMakePresetsGraph.h

@@ -453,8 +453,15 @@ public:
     return preset.OriginFile->Version;
   }
 
-  bool ReadProjectPresets(std::string const& sourceDir,
-                          bool allowNoFiles = false);
+  enum class ReadOption
+  {
+    RequireFiles,
+    AllowNoFiles,
+  };
+
+  bool ReadProjectPresets(
+    std::string const& sourceDir,
+    ReadOption readFilesOption = ReadOption::RequireFiles);
 
   std::string GetGeneratorForPreset(std::string const& presetName) const;
 
@@ -482,7 +489,7 @@ private:
     Included,
   };
 
-  bool ReadProjectPresetsInternal(bool allowNoFiles);
+  bool ReadProjectPresetsInternal(ReadOption readFilesOption);
   bool ReadJSONFile(std::string const& filename, RootType rootType,
                     ReadReason readReason, std::vector<File*>& inProgressFiles,
                     File*& file, std::string& errMsg);