cmGeneratorTarget: add method to get a filesystem-safe export name

C++ module support puts the export name in a filename. Export names with
`:` in them are not valid filenames on Windows. Add a method to escape
names as necessary.

See: #25828

Source/cmGeneratorTarget.cxx

@@ -367,6 +367,16 @@ std::string cmGeneratorTarget::GetExportName() const
   return this->GetName();
 }
 
+std::string cmGeneratorTarget::GetFilesystemExportName() const
+{
+  auto fs_safe = this->GetExportName();
+  // First escape any `_` characters to avoid collisions.
+  cmSystemTools::ReplaceString(fs_safe, "_", "__");
+  // Escape other characters that are not generally filesystem-safe.
+  cmSystemTools::ReplaceString(fs_safe, ":", "_c");
+  return fs_safe;
+}
+
 cmValue cmGeneratorTarget::GetProperty(const std::string& prop) const
 {
   if (cmValue result =

Source/cmGeneratorTarget.h

@@ -99,6 +99,7 @@ public:
   cmStateEnums::TargetType GetType() const;
   const std::string& GetName() const;
   std::string GetExportName() const;
+  std::string GetFilesystemExportName() const;
 
   std::vector<std::string> GetPropertyKeys() const;
   //! Might return a nullptr if the property is not set or invalid