Fix support for PostgreSQL timestamp fields.

PostgreSQL uses a format similar to IS8601 but allows values expressed
with tenths or hundreths of seconds rather than just milliseconds.
`2020-01-01 12:34:98.3+00` as opposed to `2020-01-01 12:34:98.300+00`,
for example. The `times` module in the Nim stdlib supports only
milliseconds with exactly three digits. To bridge this gap we detect the
two unsupported cases and pad the fractional seconds out to millisecond
precision.

src/fiber_orm/util.nim

@@ -1,14 +1,16 @@
 import json, macros, options, sequtils, strutils, times, timeutils, unicode,
   uuids
 
+import nre except toSeq
+
 const UNDERSCORE_RUNE = "_".toRunes[0]
 const PG_TIMESTAMP_FORMATS = [
   "yyyy-MM-dd HH:mm:sszz",
-  "yyyy-MM-dd HH:mm:ss'.'fzz",
-  "yyyy-MM-dd HH:mm:ss'.'ffzz",
   "yyyy-MM-dd HH:mm:ss'.'fffzz"
 ]
 
+var PG_PARTIAL_FORMAT_REGEX = re"(\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.)(\d{1,3})(\S+)?"
+
 type
   MutateClauses* = object
     columns*: seq[string]
@@ -69,9 +71,27 @@ type DbArrayParseState = enum
 
 proc parsePGDatetime*(val: string): DateTime =
   var errStr = ""
+
+  # Try to parse directly using known format strings.
   for df in PG_TIMESTAMP_FORMATS:
     try: return val.parse(df)
-    except: errStr &= "\n" & getCurrentExceptionMsg()
+    except: errStr &= "\n\t" & getCurrentExceptionMsg()
+
+  # PostgreSQL will truncate any trailing 0's in the millisecond value leading
+  # to values like `2020-01-01 16:42.3+00`. This cannot currently be parsed by
+  # the standard times format as it expects exactly three digits for
+  # millisecond values. So we have to detect this and pad out the millisecond
+  # value to 3 digits.
+  let match = val.match(PG_PARTIAL_FORMAT_REGEX)
+  if match.isSome:
+    let c = match.get.captures
+    try:
+      let corrected = c[0] & alignLeft(c[1], 3, '0') & c[2]
+      return corrected.parse(PG_TIMESTAMP_FORMATS[1])
+    except:
+      errStr &= "\n\t" & PG_TIMESTAMP_FORMATS[1] &
+        " after padding out milliseconds to full 3-digits"
+
   raise newException(ValueError, "Cannot parse PG date. Tried:" & errStr)
 
 proc parseDbArray*(val: string): seq[string] =