From 58e27ebd4a16ca9f2ba24826d7162384d5321101 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Thu, 22 Jul 2021 09:37:41 +0200
Subject: [PATCH] fixes #12815 (#18554)

---
 changelog.md           |  3 +++
 compiler/ast.nim       |  2 +-
 compiler/lineinfos.nim |  4 +++-
 compiler/sempass2.nim  |  5 ++++-
 doc/nimc.rst           |  6 ++++++
 tests/misc/tconv.nim   | 13 +++++++++++++
 6 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/changelog.md b/changelog.md
index f2a9ca9142..8e8b0a908c 100644
--- a/changelog.md
+++ b/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.
 
diff --git a/compiler/ast.nim b/compiler/ast.nim
index 8b836e0884..0eeaa81335 100644
--- a/compiler/ast.nim
+++ b/compiler/ast.nim
@@ -1064,7 +1064,7 @@ proc getPIdent*(a: PNode): PIdent {.inline.} =
   # which may simplify code.
   case a.kind
   of nkSym: a.sym.name
-  of nkIdent:  a.ident
+  of nkIdent: a.ident
   else: nil
 
 proc getnimblePkg*(a: PSym): PSym =
diff --git a/compiler/lineinfos.nim b/compiler/lineinfos.nim
index 3f31ceb974..8cb8341564 100644
--- a/compiler/lineinfos.nim
+++ b/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,
diff --git a/compiler/sempass2.nim b/compiler/sempass2.nim
index ce21c3ed28..87ed810988 100644
--- a/compiler/sempass2.nim
+++ b/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])
diff --git a/doc/nimc.rst b/doc/nimc.rst
index 0709568608..3c451706b2 100644
--- a/doc/nimc.rst
+++ b/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.
 ==========================       ============================================
 
diff --git a/tests/misc/tconv.nim b/tests/misc/tconv.nim
index 1cb4b4fbf1..ff6875021e 100644
--- a/tests/misc/tconv.nim
+++ b/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.}