undo RFC #294, it breaks code for no good reason, the compiler can wa… (#18546)

* undo RFC #294, it breaks code for no good reason, the compiler can warn about the construct instead

* Update changelog.md

Co-authored-by: konsumlamm <44230978+konsumlamm@users.noreply.github.com>

* enable test case

Co-authored-by: konsumlamm <44230978+konsumlamm@users.noreply.github.com>

changelog.md

@@ -23,15 +23,14 @@
 - `repr` now doesn't insert trailing newline; previous behavior was very inconsistent,
   see #16034. Use `-d:nimLegacyReprWithNewline` for previous behavior.
 
-- An enum now can't be converted to another enum directly, you must use `ord` (or `cast`, but
-  compiler won't help if you misuse it).
+- A type conversion from one enum type to another now produces an `[EnumConv]` warning.
+  You should use `ord` (or `cast`, but the compiler won't help, if you misuse it) instead.
   ```
   type A = enum a1, a2
   type B = enum b1, b2
-  doAssert not compiles(a1.B)
-  doAssert compiles(a1.ord.B)
+  echo a1.B # produces a warning
+  echo a1.ord.B # produces no warning
   ```
-  for a transition period, use `-d:nimLegacyConvEnumEnum`.
 
 - Type mismatch errors now show more context, use `-d:nimLegacyTypeMismatch` for previous
   behavior.

compiler/lineinfos.nim

@@ -70,6 +70,7 @@ type
     warnResultUsed = "ResultUsed",
     warnCannotOpen = "CannotOpen",
     warnFileChanged = "FileChanged",
+    warnSuspiciousEnumConv = "EnumConv",
     warnUser = "User",
     # hints
     hintSuccess = "Success", hintSuccessX = "SuccessX",
@@ -153,6 +154,7 @@ const
     warnResultUsed: "used 'result' variable",
     warnCannotOpen: "cannot open: $1",
     warnFileChanged: "file changed: $1",
+    warnSuspiciousEnumConv: "$1",
     warnUser: "$1",
     hintSuccess: "operation successful: $#",
     # keep in sync with `testament.isSuccess`

compiler/semexprs.nim

@@ -168,9 +168,7 @@ proc checkConvertible(c: PContext, targetTyp: PType, src: PNode): TConvStatus =
   elif (targetBaseTyp.kind in IntegralTypes) and
       (srcBaseTyp.kind in IntegralTypes):
     if targetTyp.kind == tyEnum and srcBaseTyp.kind == tyEnum:
-      if c.config.isDefined("nimLegacyConvEnumEnum"):
-        message(c.config, src.info, warnUser, "enum to enum conversion is now deprecated")
-      else: result = convNotLegal
+      message(c.config, src.info, warnSuspiciousEnumConv, "suspicious code: enum to enum conversion")
     # `elif` would be incorrect here
     if targetTyp.kind == tyBool:
       discard "convOk"

compiler/types.nim

@@ -1598,8 +1598,6 @@ proc typeMismatch*(conf: ConfigRef; info: TLineInfo, formal, actual: PType, n: P
       of efLockLevelsDiffer:
         msg.add "\nlock levels differ"
 
-    if formal.kind == tyEnum and actual.kind == tyEnum:
-      msg.add "\nmaybe use `-d:nimLegacyConvEnumEnum` for a transition period"
     localError(conf, info, msg)
 
 proc isTupleRecursive(t: PType, cycleDetector: var IntSet): bool =

tests/misc/tconv.nim

@@ -1,7 +1,5 @@
 discard """
-  nimout:'''
-tconv.nim(81, 15) Warning: enum to enum conversion is now deprecated [User]
-'''
+  matrix: "--warningAsError:EnumConv"
 """
 
 template reject(x) =
@@ -77,12 +75,12 @@ block: # https://github.com/nim-lang/RFCs/issues/294
   reject: k2.Goo
   reject: k2.string
 
-  {.define(nimLegacyConvEnumEnum).}
+  {.push warningAsError[EnumConv]:off.}
   discard Goo(k2)
   accept: Goo(k2)
   accept: k2.Goo
   reject: k2.string
-  {.undef(nimLegacyConvEnumEnum).}
+  {.pop.}
 
   reject: Goo(k2)
   reject: k2.Goo