errordesc.cc: Correctly append a single character to a std::string

The idiom
    char c = ...;
    _userMsg.append( &c );
is not correct C++, because it treats the address of 'c' as a NUL-
terminated C string.  However, this is not guaranteed.

When building and testing on Debian Stretch with AddressSanitizer:
    ASAN_OPTIONS="detect_leaks=false" CXX="clang++" CC=clang CXXFLAGS="-fsanitize=address" LDFLAGS="-fsanitize=address" cmake .. -DSC_ENABLE_TESTING=ON  -DSC_BUILD_SCHEMAS="ifc2x3;ap214e3;ap209"
    ASAN_OPTIONS="detect_leaks=false" make
    ASAN_OPTIONS="detect_leaks=false" ctest . --output-on-failure
an error like the following is encountered:

==15739==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffeb2ca7621 at pc 0x00000043c943 bp 0x7ffeb2ca75d0 sp 0x7ffeb2ca6d80
READ of size 33 at 0x7ffeb2ca7621 thread T0
    #0 0x43c942 in __interceptor_strlen.part.45 (/home/jepler/src/stepcode/build/bin/lazy_sdai_ap214e3+0x43c942)
    #1 0x7fb9056e6143 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::append(char const*) (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0x11f143)
    #2 0x7fb905b677c3 in ErrorDescriptor::AppendToDetailMsg(char) /home/jepler/src/stepcode/src/clutils/errordesc.cc:150:5

Address 0x7ffeb2ca7621 is located in stack of thread T0 at offset 33 in frame
    #0 0x7fb905b676af in ErrorDescriptor::AppendToDetailMsg(char) /home/jepler/src/stepcode/src/clutils/errordesc.cc:149

  This frame has 1 object(s):
    [32, 33) '' <== Memory access at offset 33 overflows this variable

A similar problem with AppendToUserMsg is found by inspection.

After this change, all 200 tests pass under the AddressSanitizer
configuration

cmake/SC_Config_Headers.cmake

@@ -80,7 +80,7 @@ std::cout << \"1s is \"<< std::chrono::duration_cast<std::chrono::milliseconds>(
   set( TEST_NULLPTR "
 #include <cstddef>
 std::nullptr_t f() {return nullptr;}
-int main() {return !!f();}
+int main() {return !(f() == f());}
   " )
   cmake_push_check_state()
   if( UNIX )

src/clutils/errordesc.cc

@@ -131,7 +131,7 @@ void ErrorDescriptor::PrependToUserMsg( const char * msg ) {
 }
 
 void ErrorDescriptor::AppendToUserMsg( const char c ) {
-    _userMsg.append( &c );
+    _userMsg.push_back( c );
 }
 
 void ErrorDescriptor::AppendToUserMsg( const char * msg ) {
@@ -147,7 +147,7 @@ void ErrorDescriptor::PrependToDetailMsg( const char * msg ) {
 }
 
 void ErrorDescriptor::AppendToDetailMsg( const char c ) {
-    _detailMsg.append( &c );
+    _detailMsg.push_back( c );
 }
 
 void ErrorDescriptor::AppendToDetailMsg( const char * msg ) {

src/express/error.c

@@ -67,6 +67,9 @@
 #include "express/info.h"
 #include "express/linklist.h"
 
+#if defined( _WIN32 ) || defined ( __WIN32__ )
+#  define snprintf _snprintf
+#endif
 
 bool __ERROR_buffer_errors = false;
 const char * current_filename = "stdin";
@@ -112,6 +115,7 @@ static struct heap_element {
 static int ERROR_with_lines = 0;    /**< number of warnings & errors that have occurred with a line number */
 static char * ERROR_string;
 static char * ERROR_string_base;
+static char * ERROR_string_end;
 
 static bool ERROR_unsafe = false;
 static jmp_buf ERROR_safe_env;
@@ -119,6 +123,34 @@ static jmp_buf ERROR_safe_env;
 
 #define error_file stderr /**< message buffer file */
 
+static int ERROR_vprintf( const char *format, va_list ap ) {
+    int result = snprintf( ERROR_string, ERROR_string_end - ERROR_string, format, ap );
+    if(result < 0) {
+        ERROR_string = ERROR_string_end;
+    } else if(result > (ERROR_string_end - ERROR_string)) {
+        ERROR_string = ERROR_string_end;
+    } else {
+        ERROR_string = ERROR_string + result;
+    }
+    return result;
+}
+
+static int ERROR_printf( const char *format, ... ) {
+    int result;
+    va_list ap;
+    va_start( ap, format );
+    result = ERROR_vprintf( format, ap );
+    va_end( ap );
+    return result;
+}
+
+static void ERROR_nexterror() {
+    if( ERROR_string == ERROR_string_end ) {
+        return;
+    }
+    ERROR_string++;
+}
+
 /** Initialize the Error module */
 void ERRORinitialize( void ) {
     ERROR_subordinate_failed =
@@ -127,6 +159,7 @@ void ERRORinitialize( void ) {
         ERRORcreate( "%s, expecting %s in %s %s", SEVERITY_EXIT );
 
     ERROR_string_base = ( char * )sc_malloc( ERROR_MAX_SPACE );
+    ERROR_string_end = ERROR_string_base + ERROR_MAX_SPACE;
     ERROR_start_message_buffer();
 
 
@@ -377,20 +410,14 @@ va_dcl {
             heap[child].msg = ERROR_string;
 
             if( what->severity >= SEVERITY_ERROR ) {
-                sprintf( ERROR_string, "%s:%d: --ERROR PE%03d: ", sym->filename, sym->line, what->serial );
-                ERROR_string += strlen( ERROR_string );
-                vsprintf( ERROR_string, what->message, args );
-                ERROR_string += strlen( ERROR_string );
-                *ERROR_string++ = '\n';
-                *ERROR_string++ = '\0';
+                ERROR_printf( "%s:%d: --ERROR PE%03d: ", sym->filename, sym->line, what->serial );
+                ERROR_vprintf( what->message, args );
+                ERROR_nexterror();
                 ERRORoccurred = true;
             } else {
-                sprintf( ERROR_string, "%s:%d: WARNING PW%03d: ", sym->filename, sym->line, what->serial );
-                ERROR_string += strlen( ERROR_string );
-                vsprintf( ERROR_string, what->message, args );
-                ERROR_string += strlen( ERROR_string );
-                *ERROR_string++ = '\n';
-                *ERROR_string++ = '\0';
+                ERROR_printf( "%s:%d: WARNING PW%03d: ", sym->filename, sym->line, what->serial );
+                ERROR_vprintf( what->message, args );
+                ERROR_nexterror();
             }
             if( what->severity >= SEVERITY_EXIT ||
                     ERROR_string + ERROR_MAX_STRLEN > ERROR_string_base + ERROR_MAX_SPACE ||
@@ -410,7 +437,6 @@ va_dcl {
                 ERRORoccurred = true;
             } else {
                 fprintf( error_file, "%s:%d: WARNING PW%03d: ", sym->filename, sym->line, what->serial );
-                ERROR_string += strlen( ERROR_string ) + 1;
                 vfprintf( error_file, what->message, args );
                 fprintf( error_file, "\n" );
             }