[ML] Correct the way internal linkage of constants is achieved (elastic#102)

1. There's no need for constants declared in unnamed namespaces
   to be declared static - they already have internal linkage.
2. Constants of type char* pointing to literals should be
   declared const char* const - declaring them const char* does
   not result in internal linkage because it allows them to be
   changed to point at something completely different!

Author: David Roberts

include/core/COsFileFuncs.h

@@ -70,7 +70,7 @@ class CORE_EXPORT COsFileFuncs : private CNonInstantiatable {
     static const int EXECUTABLE;
 
     //! The name of the magic file that discards everything written to it
-    static const char* NULL_FILENAME;
+    static const char* const NULL_FILENAME;
 
 public:
     //! Signed size type (to be used instead of ssize_t)

include/core/CProcess.h

@@ -40,10 +40,10 @@ namespace core {
 class CORE_EXPORT CProcess : private CNonCopyable {
 public:
     //! These messages need to be 100% standard across all services
-    static const char* STARTING_MSG;
-    static const char* STARTED_MSG;
-    static const char* STOPPING_MSG;
-    static const char* STOPPED_MSG;
+    static const char* const STARTING_MSG;
+    static const char* const STARTED_MSG;
+    static const char* const STOPPING_MSG;
+    static const char* const STOPPED_MSG;
 
 public:
     //! Prototype of the mlMain() function

include/core/CWordDictionary.h

@@ -149,7 +149,7 @@ class CORE_EXPORT CWordDictionary : private CNonCopyable {
 
 private:
     //! Name of the file to load that contains the dictionary words.
-    static const char* DICTIONARY_FILE;
+    static const char* const DICTIONARY_FILE;
 
     //! The constructor loads a file, and hence may take a while.  This
     //! mutex prevents the singleton object being constructed simultaneously

include/core/CXmlParser.h

@@ -59,7 +59,7 @@ class CORE_EXPORT CXmlParser : public CXmlParserIntf {
     static const std::string ATTRIBUTE_EQUALS;
     static const size_t DEFAULT_INDENT_SPACES;
     static const size_t MAX_INDENT_SPACES;
-    static const char* INDENT_SPACE_STR;
+    static const char* const INDENT_SPACE_STR;
 
 public:
     using TStrVec = std::vector<std::string>;

include/core/CoreTypes.h

@@ -17,17 +17,12 @@ using TTime = time_t;
 
 //! The standard line ending for the platform - DON'T make this std::string as
 //! that would cause many strings to be constructed (since the variable is
-//! static const at the namespace level, so is internal to each file this
-//! header is included in)
+//! const at the namespace level, so is internal to each file this header is
+//! included in)
 #ifdef Windows
-static const char* LINE_ENDING = "\r\n";
+const char* const LINE_ENDING = "\r\n";
 #else
-#ifdef __GNUC__
-// Tell g++ that it's reasonable that this variable isn't used
-__attribute__((unused)) static const char* LINE_ENDING = "\n";
-#else
-static const char* LINE_ENDING = "\n";
-#endif
+const char* const LINE_ENDING = "\n";
 #endif
 }
 }

include/model/ModelTypes.h

@@ -701,7 +701,7 @@ enum EMetricCategory {
 };
 
 //! Must correspond to the number of enumeration values of EMetricCategory
-static const size_t NUM_METRIC_CATEGORIES = 9;
+const size_t NUM_METRIC_CATEGORIES = 9;
 
 //! Get the metric feature data corresponding to \p feature
 //! if there is one.

lib/api/unittest/CIoManagerTest.cc

@@ -25,19 +25,19 @@ const uint32_t PAUSE_TIME_MS = 10;
 const size_t MAX_ATTEMPTS = 100;
 const size_t TEST_SIZE = 10000;
 const char TEST_CHAR = 'a';
-const char* GOOD_INPUT_FILE_NAME = "testfiles/good_input_file";
-const char* GOOD_OUTPUT_FILE_NAME = "testfiles/good_output_file";
+const char* const GOOD_INPUT_FILE_NAME = "testfiles/good_input_file";
+const char* const GOOD_OUTPUT_FILE_NAME = "testfiles/good_output_file";
 #ifdef Windows
-const char* GOOD_INPUT_PIPE_NAME = "\\\\.\\pipe\\good_input_pipe";
-const char* GOOD_OUTPUT_PIPE_NAME = "\\\\.\\pipe\\good_output_pipe";
+const char* const GOOD_INPUT_PIPE_NAME = "\\\\.\\pipe\\good_input_pipe";
+const char* const GOOD_OUTPUT_PIPE_NAME = "\\\\.\\pipe\\good_output_pipe";
 #else
-const char* GOOD_INPUT_PIPE_NAME = "testfiles/good_input_pipe";
-const char* GOOD_OUTPUT_PIPE_NAME = "testfiles/good_output_pipe";
+const char* const GOOD_INPUT_PIPE_NAME = "testfiles/good_input_pipe";
+const char* const GOOD_OUTPUT_PIPE_NAME = "testfiles/good_output_pipe";
 #endif
-const char* BAD_INPUT_FILE_NAME = "can't_create_a_file_here/bad_input_file";
-const char* BAD_OUTPUT_FILE_NAME = "can't_create_a_file_here/bad_output_file";
-const char* BAD_INPUT_PIPE_NAME = "can't_create_a_pipe_here/bad_input_pipe";
-const char* BAD_OUTPUT_PIPE_NAME = "can't_create_a_pipe_here/bad_output_pipe";
+const char* const BAD_INPUT_FILE_NAME = "can't_create_a_file_here/bad_input_file";
+const char* const BAD_OUTPUT_FILE_NAME = "can't_create_a_file_here/bad_output_file";
+const char* const BAD_INPUT_PIPE_NAME = "can't_create_a_pipe_here/bad_input_pipe";
+const char* const BAD_OUTPUT_PIPE_NAME = "can't_create_a_pipe_here/bad_output_pipe";
 
 class CThreadDataWriter : public ml::core::CThread {
 public:

lib/core/CMutex_Windows.cc

@@ -8,7 +8,7 @@
 namespace {
 // 4000 is a value that Microsoft uses in some of their code, so it's
 // hopefully a reasonably sensible setting
-static const DWORD SPIN_COUNT(4000);
+const DWORD SPIN_COUNT(4000);
 }
 
 namespace ml {

lib/core/COsFileFuncs.cc

@@ -27,7 +27,7 @@ const int COsFileFuncs::READABLE(R_OK);
 const int COsFileFuncs::WRITABLE(W_OK);
 const int COsFileFuncs::EXECUTABLE(X_OK);
 
-const char* COsFileFuncs::NULL_FILENAME("/dev/null");
+const char* const COsFileFuncs::NULL_FILENAME("/dev/null");
 
 int COsFileFuncs::open(const char* path, int oflag) {
     return ::open(path, oflag);

lib/core/COsFileFuncs_Windows.cc

@@ -51,7 +51,7 @@ const int COsFileFuncs::WRITABLE(2);
 // For Windows, consider "executable" the same as "readable" for the time being
 const int COsFileFuncs::EXECUTABLE(4);
 
-const char* COsFileFuncs::NULL_FILENAME("nul");
+const char* const COsFileFuncs::NULL_FILENAME("nul");
 
 int COsFileFuncs::open(const char* path, int oflag) {
     return COsFileFuncs::open(path, oflag, 0);