Re-enabled address sanitizer.

Found out what was wrong: I fed boost::regex_search() the pointer to a substring
that was created in-place. match[2] was a pointer to a substring inside that.

The problem was, that match was declared outside of the if-block. So after the
if-block match[2] would point to a now freed memory address. It didn't have any
effects because I didn't use match afterwards.

I rewrote the whole thing with iterators. Slightly less readable, slightly
better performance (probably).

cmake/debug_flags.cmake

@@ -25,7 +25,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang"
     "-Wformat=2"
     "-ftrapv"
     "-fsanitize=undefined"
-    # "-fsanitize=address"
+    "-fsanitize=address"
     "-Og"
     "-fno-omit-frame-pointer")
   if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
@@ -47,8 +47,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang"
 
   list(APPEND tmp_LDFLAGS
     "-fsanitize=undefined"
-    # "-fsanitize=address"
-    )
+    "-fsanitize=address")
   # add_link_options was introduced in version 3.13.
   if(${CMAKE_VERSION} VERSION_LESS 3.13)
     set(CMAKE_SHARED_LINKER_FLAGS_DEBUG "${tmp_LDFLAGS}")

src/search.cpp

@@ -149,12 +149,16 @@ void cleanup_text(string &text)
         else if (text.substr(pos, 6) == "<span ")
         {
             auto endpos{text.find('>')};
-            boost::match_results<const char *> match;
-            if (boost::regex_search(text.substr(pos, endpos - pos).data(),
-                                    match, re_pagebreak))
+
+            boost::match_results<string::const_iterator> match;
+            using it_size_t = string::const_iterator::difference_type;
+            string::const_iterator begin{text.begin()
+                                         + static_cast<it_size_t>(pos)};
+            string::const_iterator end{text.end()
+                                       + static_cast<it_size_t>(endpos)};
+
+            if (boost::regex_search(begin, end, match, re_pagebreak))
             {
-                // FIXME: -fsanitize=address is complaining about this. ↓ 🤷
-                //        Could not reproduce it.
                 replacement = format("<PAGE {0:s}>", match[2].str());
             }
         }
@@ -240,9 +244,9 @@ match_context context(const boost::match_results<string::const_iterator> &match,
         words -= 1;
     }
 
-    const std::string before_reversed(rbegin_before, pos_before);
+    const string before_reversed(rbegin_before, pos_before);
     string before(before_reversed.rbegin(), before_reversed.rend());
-    std::string after(begin_after, pos_after);
+    string after(begin_after, pos_after);
     while (helpers::is_whitespace(*before.begin()))
     {
         before.erase(0, 1);