[lldb] Always round down in NSDate's formatter to match NSDate's builtin format

[teemperor]

Summary

When printing an NSDate (for example with NSLog or po) the seconds value is always rounded down.
LLDB's own formatter however isn't following that behaviour which leads to situations where the
formatted result is sometimes one second off. For example:

(lldb) p [NSDate dateWithTimeIntervalSince1970:0.1]
(__NSTaggedDate *) $1 = [...] 1970-01-01 00:00:01 UTC
(lldb) po [NSDate dateWithTimeIntervalSince1970:0.1]
1970-01-01 00:00:00 +0000

(lldb) p [NSDate dateWithTimeIntervalSince1970:0.6]
(__NSTaggedDate *) $4 =[...] 1970-01-01 00:00:01 UTC
(lldb) po [NSDate dateWithTimeIntervalSince1970:0.6]
1970-01-01 00:00:00 +0000

This patch just always rounds down the seconds value we get from the NSDate object.

Fixes rdar://65084800

[mib]

LGTM!

lldb/source/Plugins/Language/ObjC/Cocoa.cpp

if (class_name == g___NSTaggedDate) {
     if (runtime && runtime->GetFoundationVersion() >= 1600)
       date_value = decodeTaggedTimeInterval(value_bits << 4);
   }
 
   // this snippet of code assumes that time_t == seconds since Jan-1-1970 this
   // is generally true and POSIXly happy, but might break if a library vendor
   // decides to get creative
   time_t epoch = GetOSXEpoch();
-  epoch = epoch + (time_t)date_value;
+  epoch = epoch + static_cast<time_t>(std::floor(date_value));
   tm *tm_date = gmtime(&epoch);
   if (!tm_date)
     return false;
   std::string buffer(1024, 0);
   if (strftime(&buffer[0], 1023, "%Z", tm_date) == 0)
     return false;
   stream.Printf("%04d-%02d-%02d %02d:%02d:%02d %s", tm_date->tm_year + 1900,
                 tm_date->tm_mon + 1, tm_date->tm_mday, tm_date->tm_hour,

lldb/test/API/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjCNSDate.py

def nsdate_data_formatter_commands(self):
 
         self.expect('frame variable date1_abs date2_abs',
                     substrs=['1985-04', '2011-01'])
 
         self.expect('frame variable date3_abs', substrs=[now_year])
         self.expect('frame variable date4_abs', substrs=['1970'])
         self.expect('frame variable date5_abs', substrs=[now_year])
 
+        # Check that LLDB always follow's NSDate's rounding behavior (which
+        # is always rounding down).
+        self.expect_expr("date_1970_minus_06", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_minus_05", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_minus_04", result_summary="1969-12-31 23:59:59 UTC")
+        self.expect_expr("date_1970_plus_06", result_summary="1970-01-01 00:00:00 UTC")
+        self.expect_expr("date_1970_plus_05", result_summary="1970-01-01 00:00:00 UTC")
+        self.expect_expr("date_1970_plus_04", result_summary="1970-01-01 00:00:00 UTC")
+
         self.expect('frame variable cupertino home europe',
                     substrs=['@"America/Los_Angeles"',
                              '@"Europe/Rome"',
                              '@"Europe/Paris"'])
 
         self.expect('frame variable cupertino_ns home_ns europe_ns',
                     substrs=['@"America/Los_Angeles"',
                              '@"Europe/Rome"',
                              '@"Europe/Paris"'])
 
         self.expect(
             'frame variable mut_bv',
             substrs=[
                 '(CFMutableBitVectorRef) mut_bv = ',
                 '1110 0110 1011 0000 1101 1010 1000 1111 0011 0101 1101 0001 00'])

lldb/test/API/functionalities/data-formatter/data-formatter-objc/main.m

int main(int argc, const char *argv[]) {
   NSDate *date2 =
       [NSDate dateWithNaturalLanguageString:@"12am January 1, 2011"];
   NSDate *date3 = [NSDate date];
   NSDate *date4 = [NSDate dateWithTimeIntervalSince1970:24 * 60 * 60];
   NSDate *date5 =
       [NSDate dateWithTimeIntervalSinceReferenceDate:
                   floor([[NSDate date] timeIntervalSinceReferenceDate])];
 
+  NSDate *date_1970_minus_06 = [NSDate dateWithTimeIntervalSince1970:-0.6];
+  NSDate *date_1970_minus_05 = [NSDate dateWithTimeIntervalSince1970:-0.5];
+  NSDate *date_1970_minus_04 = [NSDate dateWithTimeIntervalSince1970:-0.4];
+
+  NSDate *date_1970_plus_06 = [NSDate dateWithTimeIntervalSince1970:0.6];
+  NSDate *date_1970_plus_05 = [NSDate dateWithTimeIntervalSince1970:0.5];
+  NSDate *date_1970_plus_04 = [NSDate dateWithTimeIntervalSince1970:0.4];
+
   CFAbsoluteTime date1_abs = CFDateGetAbsoluteTime(date1);
   CFAbsoluteTime date2_abs = CFDateGetAbsoluteTime(date2);
   CFAbsoluteTime date3_abs = CFDateGetAbsoluteTime(date3);
   CFAbsoluteTime date4_abs = CFDateGetAbsoluteTime(date4);
   CFAbsoluteTime date5_abs = CFDateGetAbsoluteTime(date5);
 
   NSIndexSet *iset1 =
       [[NSIndexSet alloc] initWithIndexesInRange:NSMakeRange(1, 4)];