[RFC][libc++][test] Improves testing diagnostics.

libcxx/docs/TestingLibcxx.rst

@@ -329,6 +329,33 @@ additional headers.
           Since it is not expected to add this to existing tests no effort was
           taken to make it work in earlier language versions.
 
+The Standard does not provide a ``operator<<`` for ``std::source_location`` this
+header adds one. Using ``std::source_location`` allows printing messages that
+are easier to trace to the origin. When the expected result is not unique, the
+origin of the call in the source file can be written to the output. For example:
+
+.. code-block:: cpp
+
+  void test(int input,
+            int expected,
+            std::source_location loc = std::source_location::current()) {
+    int result = ...;
+    TEST_REQUIRE(result == expected,
+                TEST_WRITE_CONCATENATED(loc,
+                                        "\nExpected output ",
+                                        expected,
+                                        "\nActual output   ",
+                                        result,
+                                        '\n'));
+
+    }
+
+    int main(int, char**) {
+      test(10, 100);
+      test(20, 100);
+
+      return 0;
+    }
 
 Test names
 ----------

libcxx/test/libcxx/time/time.zone/time.zone.timezone/time.zone.members/get_info.sys_time.rule_selection.pass.cpp

@@ -83,19 +83,19 @@ static const std::chrono::tzdb& parse(std::string_view input) {
   return std::chrono::time_point_cast<std::chrono::seconds>(static_cast<std::chrono::sys_days>(result)) + h + m + s;
 }
 
-static void assert_equal(const std::chrono::sys_info& lhs, const std::chrono::sys_info& rhs) {
+static void assert_equal(const std::chrono::sys_info& lhs, const std::chrono::sys_info& rhs, std::source_location loc = std::source_location::current()) {
   TEST_REQUIRE(lhs.begin == rhs.begin,
-               TEST_WRITE_CONCATENATED("\nBegin:\nExpected output ", lhs.begin, "\nActual output   ", rhs.begin, '\n'));
+               TEST_WRITE_CONCATENATED(loc,"\nBegin:\nExpected output ", lhs.begin, "\nActual output   ", rhs.begin, '\n'));
   TEST_REQUIRE(lhs.end == rhs.end,
-               TEST_WRITE_CONCATENATED("\nEnd:\nExpected output ", lhs.end, "\nActual output   ", rhs.end, '\n'));
+               TEST_WRITE_CONCATENATED(loc,"\nEnd:\nExpected output ", lhs.end, "\nActual output   ", rhs.end, '\n'));
   TEST_REQUIRE(
       lhs.offset == rhs.offset,
-      TEST_WRITE_CONCATENATED("\nOffset:\nExpected output ", lhs.offset, "\nActual output   ", rhs.offset, '\n'));
+      TEST_WRITE_CONCATENATED(loc,"\nOffset:\nExpected output ", lhs.offset, "\nActual output   ", rhs.offset, '\n'));
   TEST_REQUIRE(lhs.save == rhs.save,
-               TEST_WRITE_CONCATENATED("\nSave:\nExpected output ", lhs.save, "\nActual output   ", rhs.save, '\n'));
+               TEST_WRITE_CONCATENATED(loc,"\nSave:\nExpected output ", lhs.save, "\nActual output   ", rhs.save, '\n'));
   TEST_REQUIRE(
       lhs.abbrev == rhs.abbrev,
-      TEST_WRITE_CONCATENATED("\nAbbrev:\nExpected output ", lhs.abbrev, "\nActual output   ", rhs.abbrev, '\n'));
+      TEST_WRITE_CONCATENATED(loc,"\nAbbrev:\nExpected output ", lhs.abbrev, "\nActual output   ", rhs.abbrev, '\n'));
 }
 
 /***** ***** TESTS ***** *****/
@@ -109,7 +109,7 @@ int main(int, const char**) {
 Z Test 0 -     LMT      1900
 0 Rule %s
 
-R Rule 1900 max - Mar 1 2u 1 Summer
+R Rule 1900 max - Mar 1 2u 1 sUMMER
 R Rule 1900 max - Oct 1 2u 0 Winter
 )");
 

libcxx/test/support/concat_macros.h

@@ -10,6 +10,7 @@
 #define TEST_SUPPORT_CONCAT_MACROS_H
 
 #include <cstdio>
+#include <source_location>
 #include <string>
 
 #include "assert_macros.h"
@@ -134,6 +135,10 @@ OutIt test_transcode(InIt first, InIt last, OutIt out_it) {
   return out_it;
 }
 
+std::ostream& operator<<(std::ostream& os, const std::source_location& loc) {
+  return os << loc.file_name() << ':' << loc.line() << ':' << loc.column();
+}
+
 template <class T>
 concept test_streamable = requires(std::stringstream& stream, T&& value) { stream << value; };