fixes #12815 (#18554)

changelog.md

@@ -36,6 +36,9 @@
   This warning will become an error in future versions! Use an explicit conversion
   like `cstring(x)` in order to silence the warning.
 
+- There is a new warning for *any* type conversion to enum that can be enabled via
+  `.warning[AnyEnumConv]:on` or `--warning:AnyEnumConv:on`.
+
 - Type mismatch errors now show more context, use `-d:nimLegacyTypeMismatch` for previous
   behavior.
 

compiler/lineinfos.nim

@@ -71,6 +71,7 @@ type
     warnCannotOpen = "CannotOpen",
     warnFileChanged = "FileChanged",
     warnSuspiciousEnumConv = "EnumConv",
+    warnAnyEnumConv = "AnyEnumConv",
     warnCstringConv = "CStringConv",
     warnUser = "User",
     # hints
@@ -156,6 +157,7 @@ const
     warnCannotOpen: "cannot open: $1",
     warnFileChanged: "file changed: $1",
     warnSuspiciousEnumConv: "$1",
+    warnAnyEnumConv: "$1",
     warnCstringConv: "$1",
     warnUser: "$1",
     hintSuccess: "operation successful: $#",
@@ -211,7 +213,7 @@ type
   TNoteKinds* = set[TNoteKind]
 
 proc computeNotesVerbosity(): array[0..3, TNoteKinds] =
-  result[3] = {low(TNoteKind)..high(TNoteKind)} - {warnObservableStores, warnResultUsed}
+  result[3] = {low(TNoteKind)..high(TNoteKind)} - {warnObservableStores, warnResultUsed, warnAnyEnumConv}
   result[2] = result[3] - {hintStackTrace, warnUninit, hintExtendedContext, hintDeclaredLoc, hintProcessingStmt}
   result[1] = result[2] - {warnProveField, warnProveIndex,
     warnGcUnsafe, hintPath, hintDependency, hintCodeBegin, hintCodeEnd,

compiler/sempass2.nim

@@ -1171,7 +1171,10 @@ proc track(tracked: PEffects, n: PNode) =
         not allowCStringConv(n[1]):
       message(tracked.config, n.info, warnCstringConv,
         "implicit conversion to 'cstring' from a non-const location: $1; this will become a compile time error in the future" %
-          [$n[1]])
+          $n[1])
+
+    if n.typ.skipTypes(abstractInst).kind == tyEnum:
+      message(tracked.config, n.info, warnAnyEnumConv, "enum conversion: $1" % $n[1])
 
     if n.len == 2:
       track(tracked, n[1])

doc/nimc.rst

@@ -70,6 +70,12 @@ SmallLshouldNotBeUsed            The letter 'l' should not be used as an
                                  identifier.
 EachIdentIsTuple                 The code contains a confusing `var`
                                  declaration.
+CStringConv                      Warn about dangerous implicit conversions
+                                 to `cstring`.
+EnumConv                         Warn about conversions from enum to enum.
+AnyEnumConv                      Warn about any conversions to an enum type.
+ResultUsed                       Warn about the usage of the
+                                 built-in `result` variable.
 User                             Some user-defined warning.
 ==========================       ============================================
 

tests/misc/tconv.nim

@@ -92,3 +92,16 @@ reject:
     x[0] = c
     x
 
+{.push warning[AnyEnumConv]:on, warningAsError[AnyEnumConv]:on.}
+
+reject:
+  # bug #12815
+  type
+    Foo = enum
+      one = 1
+      three = 3
+
+  var va = 2
+  var vb = va.Foo
+
+{.pop.}