fix nim-lang#18007: std/json now serializes nan,inf,-inf as raw strin…

…gs instead of invalid json

changelog.md

@@ -70,6 +70,8 @@
 - `jsonutils` now serializes/deserializes holey enums as regular enums (via `ord`) instead of as strings.
   Use `-d:nimLegacyJsonutilsHoleyEnum` for a transition period.
 
+- `json` and `jsonutils` now serialize NaN, Inf, -Inf as "nan", "inf", "-inf", using raw strings (the same
+  that are used to encode numbers that can't fit in native number types).
 
 ## Standard library additions and changes
 - Added support for parenthesized expressions in `strformat`

lib/pure/json.nim

@@ -333,7 +333,10 @@ proc `%`*(n: BiggestInt): JsonNode =
 
 proc `%`*(n: float): JsonNode =
   ## Generic constructor for JSON data. Creates a new `JFloat JsonNode`.
-  result = JsonNode(kind: JFloat, fnum: n)
+  if n != n: newJRawNumber("nan")
+  elif n == Inf: newJRawNumber("inf")
+  elif n == -Inf: newJRawNumber("-inf")
+  else: JsonNode(kind: JFloat, fnum: n)
 
 proc `%`*(b: bool): JsonNode =
   ## Generic constructor for JSON data. Creates a new `JBool JsonNode`.
@@ -1087,11 +1090,32 @@ when defined(nimFixedForwardGeneric):
       dst = cast[T](jsonNode.num)
 
   proc initFromJson[T: SomeFloat](dst: var T; jsonNode: JsonNode; jsonPath: var string) =
-    verifyJsonKind(jsonNode, {JInt, JFloat}, jsonPath)
-    if jsonNode.kind == JFloat:
-      dst = T(jsonNode.fnum)
+    if jsonNode.isUnquoted:
+      assert jsonNode.kind == JString # instead of exception, because isUnquoted is internal logic
+      # when nimvm:
+      when true:
+        case jsonNode.str
+        of "nan":
+          let b = NaN
+          dst = T(b)
+          # dst = NaN # would fail some tests because range conversions would cause CT error
+          # in some cases; but this is not a hot-spot inside this branch and backend can optimize
+          # this.
+        of "inf":
+          let b = Inf
+          dst = T(b)
+        of "-inf":
+          let b = -Inf
+          dst = T(b)
+        else: raise newException(JsonKindError, "expected 'nan|inf|-inf', got " & jsonNode.str)
+      else:
+        discard
     else:
-      dst = T(jsonNode.num)
+      verifyJsonKind(jsonNode, {JInt, JFloat}, jsonPath)
+      if jsonNode.kind == JFloat:
+        dst = T(jsonNode.fnum)
+      else:
+        dst = T(jsonNode.num)
 
   proc initFromJson[T: enum](dst: var T; jsonNode: JsonNode; jsonPath: var string) =
     verifyJsonKind(jsonNode, {JString}, jsonPath)

tests/stdlib/tjson.nim

@@ -301,6 +301,12 @@ block: # bug #17383
     testRoundtrip(int64.high): "9223372036854775807"
     testRoundtrip(uint64.high): "18446744073709551615"
 
+block: # bug #18007
+  testRoundtrip([NaN, Inf, -Inf, 0.0, -0.0, 1.0]): "[nan,inf,-inf,0.0,-0.0,1.0]"
+  # pending https://github.com/nim-lang/Nim/issues/18025 use:
+  # testRoundtrip([float32(NaN), Inf, -Inf, 0.0, -0.0, 1.0]): "[nan,inf,-inf,0.0,-0.0,1.0]"
+  let inf = float32(Inf)
+  testRoundtrip([float32(NaN), inf, -inf, 0.0, -0.0, 1.0]): "[nan,inf,-inf,0.0,-0.0,1.0]"
 
 block:
   let a = "18446744073709551615"

tests/stdlib/tjsonutils.nim

@@ -91,6 +91,10 @@ template fn() =
       else:
         testRoundtrip(a): "[9223372036854775807,18446744073709551615]"
 
+  block: # bug #18007
+    testRoundtrip((NaN, Inf, -Inf, 0.0, -0.0, 1.0)): "[nan,inf,-inf,0.0,-0.0,1.0]"
+    testRoundtrip((float32(NaN), Inf, -Inf, 0.0, -0.0, 1.0)): "[nan,inf,-inf,0.0,-0.0,1.0]"
+
   block: # case object
     type Foo = object
       x0: float