Fix Time.new with String argument and handle nanoseconds correctly

Author: andrykonchin

CHANGELOG.md

@@ -6,6 +6,7 @@ New features:
 Bug fixes:
 
 * Fix `Range#cover?` on begin-less ranges and non-integer values (@nirvdrum, @rwstauner).
+* Fix `Time.new` with String argument and handle nanoseconds correctly (#3836, @andrykonchin).
 
 Compatibility:
 

spec/ruby/core/time/new_spec.rb

@@ -524,6 +524,36 @@ def obj.to_int; 3; end
       Time.new("2021-12-25 00:00:00.123456789876 +09:00", precision: 3r).subsec.should == 0.123r
     end
 
+    it "returns Time with correct subseconds when given seconds fraction is shorted than 6 digits" do
+      Time.new("2020-12-25T00:56:17.123 +09:00").nsec.should == 123000000
+      Time.new("2020-12-25T00:56:17.123 +09:00").usec.should == 123000
+      Time.new("2020-12-25T00:56:17.123 +09:00").subsec.should == 0.123
+    end
+
+    it "returns Time with correct subseconds when given seconds fraction is milliseconds" do
+      Time.new("2020-12-25T00:56:17.123456 +09:00").nsec.should == 123456000
+      Time.new("2020-12-25T00:56:17.123456 +09:00").usec.should == 123456
+      Time.new("2020-12-25T00:56:17.123456 +09:00").subsec.should == 0.123456
+    end
+
+    it "returns Time with correct subseconds when given seconds fraction is longer that 6 digits but shorted than 9 digits" do
+      Time.new("2020-12-25T00:56:17.12345678 +09:00").nsec.should == 123456780
+      Time.new("2020-12-25T00:56:17.12345678 +09:00").usec.should == 123456
+      Time.new("2020-12-25T00:56:17.12345678 +09:00").subsec.should == 0.12345678
+    end
+
+    it "returns Time with correct subseconds when given seconds fraction is nanoseconds" do
+      Time.new("2020-12-25T00:56:17.123456789 +09:00").nsec.should == 123456789
+      Time.new("2020-12-25T00:56:17.123456789 +09:00").usec.should == 123456
+      Time.new("2020-12-25T00:56:17.123456789 +09:00").subsec.should == 0.123456789
+    end
+
+    it "returns Time with correct subseconds when given seconds fraction is longer than 9 digits" do
+      Time.new("2020-12-25T00:56:17.123456789876 +09:00").nsec.should == 123456789
+      Time.new("2020-12-25T00:56:17.123456789876 +09:00").usec.should == 123456
+      Time.new("2020-12-25T00:56:17.123456789876 +09:00").subsec.should == 0.123456789
+    end
+
     ruby_version_is ""..."3.3" do
       it "raise TypeError is can't convert precision keyword argument into Integer" do
         -> {

src/main/java/org/truffleruby/core/time/TimeNodes.java

@@ -532,7 +532,7 @@ RubyTime timeSFromArray(
                 Object utcoffset) {
             final RubyLanguage language = getLanguage();
 
-            if (nsec < 0 || nsec > 999999999 ||
+            if (nsec < 0 || nsec > 999_999_999 ||
                     sec < 0 || sec > 60 || // MRI accepts sec=60, whether it is a leap second or not
                     min < 0 || min > 59 ||
                     hour < 0 || hour > 23 ||

src/main/ruby/truffleruby/core/truffle/time_operations.rb

@@ -92,6 +92,7 @@ def self.compose(time_class, utc_offset, p1, p2 = nil, p3 = nil, p4 = nil, p5 =
       Primitive.time_s_from_array(time_class, sec, min, hour, mday, month, year, nsec, is_dst, is_utc, utc_offset)
     end
 
+    # MRI: time_init_parse()
     def self.new_from_string(time_class, str, **options)
       raise ArgumentError, 'time string should have ASCII compatible encoding' unless str.encoding.ascii_compatible?
 
@@ -103,9 +104,23 @@ def self.new_from_string(time_class, str, **options)
                [ T] (?<hour> \d{2})
                   : (?<min>  \d{2})
                   : (?<sec>  \d{2})
-                  (?:\. (?<usec> \d+) )?
+                  (?:\. (?<subsec> \d+) )?
               (?:\s* (?<offset>\S+))?
              )?\z/x =~ str
+
+        # convert seconds fraction to milliseconds
+        usec = if subsec
+                 ndigits = subsec.length
+
+                 if ndigits <= 6
+                   subsec.to_i * 10.pow(6 - ndigits)
+                 else
+                   subsec.to_r / 10.pow(ndigits - 6) # convert to Rational to not loose precision
+                 end
+               else
+                 nil
+               end
+
         return self.compose(time_class, self.utc_offset_for_compose(offset || options[:in]), year, month, mday, hour, min, sec, usec)
       end