Document source_location

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 This documentation is
 
-* Copyright 2002, 2007, 2014, 2017 Peter Dimov
+* Copyright 2002, 2007, 2014, 2017, 2019 Peter Dimov
 * Copyright 2011 Beman Dawes
 * Copyright 2015 Ion Gaztañaga
 * Distributed under the http://www.boost.org/LICENSE_1_0.txt[Boost Software License, Version 1.0].

doc/source_location.adoc

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+////
+Copyright 2019 Peter Dimov
+Distributed under the Boost Software License, Version 1.0.
+http://www.boost.org/LICENSE_1_0.txt
+////
+
+# Source Location Support, <boost/assert/source_location.hpp>
+:toc:
+:toc-title:
+:idprefix:
+
+## Description
+
+The header `<boost/assert/source_location.hpp>` defines `source_location`,
+a class representing a source location and containing file, line, function
+and column information. It's similar to `std::source_location` from {cpp}20,
+but only requires {cpp}03.
+
+The macro `BOOST_CURRENT_LOCATION` creates a `source_location` object
+containing information about the current source location.
+
+## Synopsis
+
+```
+namespace boost
+{
+
+struct source_location
+{
+  constexpr source_location() noexcept;
+  constexpr source_location(char const* file, uint_least32_t line,
+    char const* function, uint_least32_t column = 0) noexcept;
+
+  constexpr char const* file_name() const noexcept;
+  constexpr char const* function_name() const noexcept;
+  constexpr uint_least32_t line() const noexcept;
+  constexpr uint_least32_t column() const noexcept;
+};
+
+} // namespace boost
+
+#define BOOST_CURRENT_LOCATION \
+  ::boost::source_location(__FILE__, __LINE__, BOOST_CURRENT_FUNCTION)
+```
+
+## source_location
+
+```
+constexpr source_location() noexcept;
+```
+
+Effects: :: Constructs a `source_location` object for which `file_name()`
+and `function_name()` return `"(unknown)"`, and `line()` and `column()`
+return `0`.
+
+```
+constexpr source_location(char const* file, uint_least32_t line,
+  char const* function, uint_least32_t column = 0) noexcept;
+```
+
+Effects: :: Constructs a `source_location` object for which `file_name()`
+returns `file`, `function_name()` returns `function`, `line()` returns the
+`line` argument and `column()` returns the `column` argument.
+
+## BOOST_CURRENT_LOCATION
+
+When `BOOST_DISABLE_CURRENT_LOCATION` is not defined, the definition of
+`BOOST_CURRENT_LOCATION` is:
+
+```
+#define BOOST_CURRENT_LOCATION \
+  ::boost::source_location(__FILE__, __LINE__, BOOST_CURRENT_FUNCTION)
+```
+
+Otherwise, `BOOST_CURRENT_LOCATION` is defined as:
+
+```
+#define BOOST_CURRENT_LOCATION ::boost::source_location()
+```
+
+This allows producing executables that contain no identifying information,
+for security reasons.