make dragonbox opt-in via -d:nimFpRoundtrips (#18504)

* make dragonbox opt-in via -d:nimFpRoundtrips

* make tests green again

* make tests green again

changelog.md

@@ -76,9 +76,6 @@
 - `json` and `jsonutils` now serialize NaN, Inf, -Inf as strings, so that
   `%[NaN, -Inf]` is the string `["nan","-inf"]` instead of `[nan,-inf]` which was invalid json.
 
-- `system.addFloat` now uses the "Dragonbox" algorithm, which ensures correct roundtrips of floating point
-  numbers, that the minimum length representation of a floating point number is used and correct rounding.
-  Use `-d:nimLegacyAddFloat` for a transition period.
 
 - `strformat` is now part of `include std/prelude`.
 
@@ -102,6 +99,12 @@
   added support for parenthesized expressions.
   added support for const string's instead of just string literals
 
+
+- `system.addFloat` and `system.$` now can produce string representations of floating point numbers
+  that are minimal in size and that "roundtrip" (via the "Dragonbox" algorithm). This currently has
+  to be enabled via `-d:nimFpRoundtrips`. It is expected that this behavior becomes the new default
+  in upcoming versions.
+
 - Fixed buffer overflow bugs in `net`
 
 - Exported `sslHandle` from `net` and `asyncnet`.
@@ -116,8 +119,6 @@
   the OpenSSL DLLs (e.g. libssl-1_1-x64.dll, libcrypto-1_1-x64.dll) you
   now also need to ship `cacert.pem` with your `.exe` file.
 
-- Make `{.requiresInit.}` pragma to work for `distinct` types.
-
 - `typetraits`:
   `distinctBase` now is identity instead of error for non distinct types.
   Added `enumLen` to return the number of elements in an enum.
@@ -468,7 +469,6 @@
   with `--styleCheck:error` or `--styleCheck:hint`.
 
 
-
 ## Tool changes
 
 - Latex doc generation is revised: output `.tex` files should be compiled

lib/system/formatfloat.nim

@@ -7,7 +7,7 @@
 #    distribution, for details about the copyright.
 #
 
-when not defined(nimLegacyAddFloat) and not defined(nimscript) and
+when defined(nimFpRoundtrips) and not defined(nimscript) and
     not defined(js) and defined(nimHasDragonBox):
   import dragonbox
 

lib/system/strmantle.nim

@@ -97,7 +97,7 @@ proc nimFloatToStr(f: float): string {.compilerproc.} =
   result = newStringOfCap(8)
   result.addFloat f
 
-when not defined(nimLegacyAddFloat) and not defined(nimscript) and
+when defined(nimFpRoundtrips) and not defined(nimscript) and
     not defined(js) and defined(nimHasDragonBox):
   import schubfach
 

tests/errmsgs/treportunused.nim

@@ -13,12 +13,12 @@ treportunused.nim(30, 5) Hint: 's8' is declared but not used [XDeclaredButNotUse
 treportunused.nim(31, 5) Hint: 's9' is declared but not used [XDeclaredButNotUsed]
 treportunused.nim(32, 6) Hint: 's10' is declared but not used [XDeclaredButNotUsed]
 treportunused.nim(33, 6) Hint: 's11' is declared but not used [XDeclaredButNotUsed]
-treportunused.nim(37, 3) Hint: 'v0.99' is declared but not used [XDeclaredButNotUsed]
-treportunused.nim(38, 3) Hint: 'v0.99.99' is declared but not used [XDeclaredButNotUsed]
 '''
 action: compile
 """
 
+#treportunused.nim(37, 3) Hint: 'v0.99' is declared but not used [XDeclaredButNotUsed]
+#treportunused.nim(38, 3) Hint: 'v0.99.99' is declared but not used [XDeclaredButNotUsed]
 # bug #9764
 iterator s1(a:string): int = discard
 iterator s2(): int = discard
@@ -32,6 +32,8 @@ var s9: int
 type s10 = object
 type s11 = type(1.2)
 
+when false:
+  # enabled again when Nim bootstraps with -d:nimFpRoundtrips
   # https://github.com/nim-lang/Nim/issues/14407
   let
     `v0.99` = "0.99"

tests/float/nim.cfg

@@ -0,0 +1 @@
+-d:nimFpRoundtrips

tests/float/tfloats.nim

@@ -66,6 +66,8 @@ template main =
     var a = 1.1'f32
     doAssert $a == "1.1", $a # was failing
 
+proc runtimeOnlyTests =
+  # enable for 'static' once -d:nimFpRoundtrips became the default
   block: # bug #7717
     proc test(f: float) =
       let f2 = $f
@@ -82,3 +84,5 @@ template main =
 
 static: main()
 main()
+
+runtimeOnlyTests()

tests/stdlib/tjson.nim

@@ -303,7 +303,7 @@ let jsonNode = %*mynode
 doAssert $jsonNode == """{"kind":"P","pChildren":[{"kind":"Text","textStr":"mychild"},{"kind":"Br"}]}"""
 doAssert $jsonNode.to(ContentNode) == """(kind: P, pChildren: @[(kind: Text, textStr: "mychild"), (kind: Br)])"""
 
-block: # bug #17383
+when defined(nimFpRoundtrips): # bug #17383
   testRoundtrip(int32.high): "2147483647"
   testRoundtrip(uint32.high): "4294967295"
   when int.sizeof == 4:
@@ -316,7 +316,7 @@ block: # bug #17383
     testRoundtrip(int64.high): "9223372036854775807"
     testRoundtrip(uint64.high): "18446744073709551615"
 
-block: # bug #18007
+when defined(nimFpRoundtrips): # 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])
@@ -332,7 +332,7 @@ block: # bug #18007
     testRoundtripVal(0.0): "0.0"
     testRoundtripVal(-0.0): "-0.0"
 
-block: # bug #15397, bug #13196
+when defined(nimFpRoundtrips): # bug #15397, bug #13196
   testRoundtripVal(1.0 + epsilon(float64)): "1.0000000000000002"
   testRoundtripVal(0.12345678901234567890123456789): "0.12345678901234568"
 

tests/stdlib/tjsonutils.nim

@@ -161,6 +161,7 @@ template fn() =
     doAssert b[2].signbit
     doAssert not b[3].signbit
 
+  when defined(nimFpRoundtrips):
     block: # bug #15397, bug #13196
       let a = 0.1
       let x = 0.12345678901234567890123456789