ENH: Add C++ script to add in-class {} member initializers to ITK

The script that was used for the following pull requests:

pull request InsightSoftwareConsortium#3851
"STYLE: Add in-class `{}` member initializers to objects created by New()"

pull request InsightSoftwareConsortium#3913
"STYLE: Add in-class `{}` initializers to classes with virtual functions"

pull request InsightSoftwareConsortium#3917
"STYLE: Add in-class `{}` initializers to classes with override = default"

pull request InsightSoftwareConsortium#3941
"STYLE: Add in-class `{}` member initializers to 3-letter data members"

pull request InsightSoftwareConsortium#3945
"STYLE: Add in-class `{}` member initializers having trailing comments"

Utilities/Maintenance/AddEmptyDefaultMemberInitializers.cxx

@@ -0,0 +1,242 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// Script to add in-class {} member initializers to ITK classes that have one or more virtual member function,
+// itkNewMacro, itkSimpleNewMacro, or itkCreateAnotherMacro calls.
+//
+// Tested with Visual Studio 2022 (C++14).
+//
+// Needs to have the directory path to the ITK sources as command-line argument, for example:
+//
+//     AddEmptyDefaultMemberInitializers.exe D:\src\ITK\Modules
+//
+// Initial version by Niels Dekker, LKEB, Leiden University Medical Center, 2023
+
+#define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
+
+#include <cassert>
+#include <cctype>
+#include <cstring>
+#include <deque>
+#include <experimental/filesystem>
+#include <fstream>
+#include <iostream>
+#include <regex>
+#include <sstream>
+#include <string>
+
+using namespace std::experimental::filesystem::v1;
+
+namespace
+{
+using Lines = std::deque<std::string>;
+
+auto
+ReadFile(const path & filePath)
+{
+  Lines result;
+
+  std::ifstream inputFileStream{ filePath };
+  std::string   line;
+  while (std::getline(inputFileStream, line))
+  {
+    result.push_back(line);
+  }
+  return result;
+}
+
+void
+WriteFile(const path & filePath, const Lines & lines)
+{
+  std::ofstream outputFileStream{ filePath };
+  for (const auto & line : lines)
+  {
+    outputFileStream << line << '\n';
+  }
+}
+
+template <unsigned int VLength>
+bool
+StringStartsWith(const std::string & str, const char (&substr)[VLength])
+{
+  assert(substr[VLength - 1] == '\0');
+  return str.compare(0, VLength - 1, substr) == 0;
+}
+
+template <unsigned int VLength>
+bool
+StringEndsWith(const std::string & str, const char (&substr)[VLength])
+{
+  assert(substr[VLength - 1] == '\0');
+  return str.size() >= VLength && str.compare(str.size() + 1 - VLength, VLength - 1, substr) == 0;
+}
+
+unsigned int
+AddInitializers(Lines & lines)
+{
+  auto numberOfAddedInitializers = 0u;
+
+  bool shouldThisClassHaveInitializers{ false };
+
+  for (auto & line : lines)
+  {
+    const auto lineStartsWith = [&line](const auto & substr) { return StringStartsWith(line, substr); };
+    const auto lineEndsWith = [&line](const auto & substr) { return StringEndsWith(line, substr); };
+    const auto lineContains = [&line](const auto & substr) { return line.find(substr) != std::string::npos; };
+
+    const auto numberOfChars = line.size();
+
+    if (numberOfChars > 0)
+    {
+      if (lineStartsWith("  itkNewMacro(") || lineStartsWith("  itkSimpleNewMacro(") ||
+          lineStartsWith("  itkCreateAnotherMacro(") || lineStartsWith("  virtual ") || lineEndsWith(" override") ||
+          lineEndsWith(" override;") || lineEndsWith(" override = default;"))
+      {
+        // We assume that a class should *certainly* have in-class data member initializers when it has a call to one
+        // of those macro's (itkNewMacro, itkSimpleNewMacro, or itkCreateAnotherMacro), or when it has a virtual member
+        // function. The creation of an object of such a class is already quite expensive (relative to a simple data
+        // struct), so the extra potential performance penalty of initializing all of its data should be neglectable.
+        shouldThisClassHaveInitializers = true;
+      }
+      else
+      {
+        if (shouldThisClassHaveInitializers)
+        {
+          if (lineStartsWith("};"))
+          {
+            // Class definition ended here.
+            shouldThisClassHaveInitializers = false;
+          }
+          else
+          {
+            // Note: Data members of type std::unique_ptr<T> or itk::SmartPointer<T> are excluded from automatically
+            // adding initializers, because they _might_ get compilation errors from GCC (prior to GCC release 9.2) when
+            // the template argument T is an incomplete type (a forwarded class) as addressed by Simon Rit:
+            // - pull request https://github.com/InsightSoftwareConsortium/ITK/pull/3877
+            // - commit eac289d25221d8e080a0ad6d2e6ce6ff0a2c576a
+            // - "COMP: Remove in-class {} member initializers of unique_ptr"
+            // - pull request https://github.com/InsightSoftwareConsortium/ITK/pull/3927
+            // - commit f5f83678755319e35c225bfe563fb26ef1d0197e
+            // - "COMP: Remove in class init of SmartPointer of forward declaration"
+            // Data members of a C++ reference type (" & m_") and `static` data members are also excluded.
+            // `m_ColorTable` was excluded, to avoid GCC warnings saying "const/copy propagation disabled " and " GCSE
+            // disabled " [-Wdisabled-optimization], at line
+            // https://github.com/InsightSoftwareConsortium/ITK/blob/v5.3.0/Modules/Core/Common/include/itkOctree.h#L222
+
+            if (lineStartsWith("  ") && lineContains(" m_") && !lineContains(" & m_") && !lineContains(" static ") &&
+                !lineContains(" std::unique_ptr<") && !lineContains("SmartPointer<") &&
+                !lineContains("m_ColorTable[ColorTableSize];"))
+            {
+              // The regular expression explicitly skips lines of code that have a `)` at the end, like
+              // `  itkSetVectorMacro(NumberOfIterations, unsigned int, m_NumberOfLevels);`, from
+              // https://github.com/InsightSoftwareConsortium/ITK/blob/v5.3.0/Modules/Registration/PDEDeformable/include/itkMultiResolutionPDEDeformableRegistration.h#L224
+
+              if (std::regex_match(line, std::regex{ R"delimiter(  \w.* m_\w([^{}=]*[^{}=\)])?;)delimiter" }))
+              {
+                line.pop_back();
+                line.append("{};");
+                std::cout << line << '\n';
+                ++numberOfAddedInitializers;
+              }
+              else
+              {
+                // Address lines of code that have a trailing C++ comment.
+                std::match_results<std::string::const_iterator> results;
+                if (std::regex_match(
+                      line,
+                      results,
+                      std::regex{ R"delimiter((  \w.* m_\w(?:[^{}=]*[^{}=\)])?);([ ]+/[/\*].+))delimiter" }) &&
+                    results.size() == 3)
+                {
+                  line = results[1].str() + "{};" + results[2].str();
+                  std::cout << line << '\n';
+                  ++numberOfAddedInitializers;
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+  return numberOfAddedInitializers;
+}
+
+auto
+ProcessFile(const path & filePath)
+{
+  auto       lines = ReadFile(filePath);
+  const auto numberOfAddedInitializers = AddInitializers(lines);
+  if (numberOfAddedInitializers > 0)
+  {
+    std::cout << "Added " << numberOfAddedInitializers << " initializer(s) to " << filePath.string() << std::endl;
+    WriteFile(filePath, lines);
+  }
+  return numberOfAddedInitializers;
+}
+
+void
+ProcessDirectory(const path & directoryPath)
+{
+  auto numberOfAddedInitializers = 0u;
+
+  for (const auto & entry : recursive_directory_iterator{ directoryPath })
+  {
+    const auto & path = entry.path();
+    const auto & extension = path.extension();
+
+    if ((!extension.empty()) && extension.string() == ".h" && StringStartsWith(path.stem().string(), "itk") &&
+        is_regular_file(path))
+    {
+      numberOfAddedInitializers += ProcessFile(path);
+    }
+  }
+  std::cout << "Added in total " << numberOfAddedInitializers << " initializer(s) to " << directoryPath.string()
+            << std::endl;
+}
+} // namespace
+
+
+int
+main(int argc, char ** argv)
+{
+  if (argc != 2)
+  {
+    std::cout << "Please specify the source directory path as command-line argument."
+                 "\nNote: This program will modify the source files in-place!!!"
+              << std::endl;
+  }
+  else
+  {
+    if (argv == nullptr)
+    {
+      return EXIT_FAILURE;
+    }
+    const char * const arg = argv[1];
+
+    if (arg == nullptr)
+    {
+      return EXIT_FAILURE;
+    }
+    ProcessDirectory(arg);
+  }
+
+  std::cout << "Press anything to continue" << std::endl;
+  std::cin.get();
+  return EXIT_SUCCESS;
+}