schema: sort dictionary fields by key

Size of the value is a compelling alternative but cannot be
inferred at code generation time.

src/preserves/preserves_schema_nim.nim

@@ -597,7 +597,13 @@ proc addFields(recList: PNode; loc: Location; known: var TypeTable; pat: Pattern
   reclist
 
 proc addFields(recList: PNode; loc: Location; known: var TypeTable; entries: DictionaryEntries; parentName: string): PNode {.discardable.} =
+  var sortedEntries =
+    initOrderedTable[Preserve[void], NamedSimplePattern](entries.len)
   for key, val in entries.pairs:
+    sortedEntries[key] = val
+  sort(sortedEntries) do (x, y: (Preserve[void], NamedSimplePattern)) -> int:
+    cmp(x[0], y[0])
+  for key, val in sortedEntries.pairs:
     doAssert(key.isSymbol)
     let label = string key.symbol
     addField(recList, loc, known, val.pattern, label)

src/preserves/private/parse.nim

@@ -4,7 +4,10 @@
 # this module is included in ../../preserves.nim
 
 import std/[parseutils, unicode]
-from std/sequtils import insert
+
+when isMainModule:
+  from std/sequtils import insert
+
 from std/strutils import Whitespace, parseFloat, parseHexStr, parseInt, tokenize
 import npeg
 import ../pegs