closed ambiguous enum defaults to first overload (#20457)

* closed ambiguous enum defaults to first overload

* add warning

* turn to hint

* work around config

5 files changed, 23 insertions, 6 deletions

diff --git a/compiler/condsyms.nim b/compiler/condsyms.nim
index 332a802ab..10f4b86ab 100644
--- a/compiler/condsyms.nim
+++ b/compiler/condsyms.nim
@@ -143,3 +143,4 @@ proc initDefines*(symbols: StringTableRef) =
   defineSymbol("nimHasTopDownInference")
   defineSymbol("nimHasTemplateRedefinitionPragma")
   defineSymbol("nimHasCstringCase")
+  defineSymbol("nimHasAmbiguousEnumHint")
diff --git a/compiler/lineinfos.nim b/compiler/lineinfos.nim
index ec1643960..05f4eba5a 100644
--- a/compiler/lineinfos.nim
+++ b/compiler/lineinfos.nim
@@ -96,6 +96,7 @@ type
     hintPattern = "Pattern", hintExecuting = "Exec", hintLinking = "Link", hintDependency = "Dependency",
     hintSource = "Source", hintPerformance = "Performance", hintStackTrace = "StackTrace",
     hintGCStats = "GCStats", hintGlobalVar = "GlobalVar", hintExpandMacro = "ExpandMacro",
+    hintAmbiguousEnum = "AmbiguousEnum",
     hintUser = "User", hintUserRaw = "UserRaw", hintExtendedContext = "ExtendedContext",
     hintMsgOrigin = "MsgOrigin", # since 1.3.5
     hintDeclaredLoc = "DeclaredLoc", # since 1.5.1
@@ -209,6 +210,7 @@ const
     hintGCStats: "$1",
     hintGlobalVar: "global variable declared here",
     hintExpandMacro: "expanded macro: $1",
+    hintAmbiguousEnum: "$1",
     hintUser: "$1",
     hintUserRaw: "$1",
     hintExtendedContext: "$1",
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index a0753010a..0c6500408 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -87,6 +87,14 @@ proc semExprWithType(c: PContext, n: PNode, flags: TExprFlags = {}, expectedType
   result = semExprCheck(c, n, flags, expectedType)
   if result.typ == nil and efInTypeof in flags:
     result.typ = c.voidType
+  elif (result.typ == nil or result.typ.kind == tyNone) and
+      result.kind == nkClosedSymChoice and
+      result[0].sym.kind == skEnumField:
+    # if overloaded enum field could not choose a type from a closed list,
+    # choose the first resolved enum field, i.e. the latest in scope
+    # to mirror old behavior
+    msgSymChoiceUseQualifier(c, result, hintAmbiguousEnum)
+    result = result[0]
   elif result.typ == nil or result.typ == c.enforceVoidContext:
     localError(c.config, n.info, errExprXHasNoType %
                 renderTree(result, {renderNoComments}))
diff --git a/compiler/semstmts.nim b/compiler/semstmts.nim
index 1b98f5c1a..4f01f508e 100644
--- a/compiler/semstmts.nim
+++ b/compiler/semstmts.nim
@@ -574,9 +574,13 @@ proc semVarMacroPragma(c: PContext, a: PNode, n: PNode): PNode =
                 pragma(c, defs[lhsPos][namePos].sym, defs[lhsPos][pragmaPos], validPragmas)
         return result
 
-proc errorSymChoiceUseQualifier(c: PContext; n: PNode) =
+proc msgSymChoiceUseQualifier(c: PContext; n: PNode; note = errGenerated) =
   assert n.kind in nkSymChoices
-  var err = "ambiguous identifier: '" & $n[0] & "'"
+  var err =
+    if note == hintAmbiguousEnum:
+      "ambiguous enum field '$1' assumed to be of type $2, this will become an error in the future" % [$n[0], typeToString(n[0].typ)]
+    else:
+      "ambiguous identifier: '" & $n[0] & "'"
   var i = 0
   for child in n:
     let candidate = child.sym
@@ -584,7 +588,7 @@ proc errorSymChoiceUseQualifier(c: PContext; n: PNode) =
     else: err.add "\n"
     err.add "  " & candidate.owner.name.s & "." & candidate.name.s
     inc i
-  localError(c.config, n.info, errGenerated, err)
+  message(c.config, n.info, note, err)
 
 proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
   var b: PNode
@@ -611,8 +615,8 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
     if a[^1].kind != nkEmpty:
       def = semExprWithType(c, a[^1], {}, typ)
 
-      if def.kind in nkSymChoices and def[0].typ.skipTypes(abstractInst).kind == tyEnum:
-        errorSymChoiceUseQualifier(c, def)
+      if def.kind in nkSymChoices and def[0].sym.kind == skEnumField:
+        msgSymChoiceUseQualifier(c, def, errGenerated)
       elif def.kind == nkSym and def.sym.kind in {skTemplate, skMacro}:
         typFlags.incl taIsTemplateOrMacro
       elif def.typ.kind == tyTypeDesc and c.p.owner.kind != skMacro:
diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index 0a823f20a..d033d5f44 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -591,7 +591,9 @@ proc semCaseBranch(c: PContext, t, branch: PNode, branchIndex: int,
       branch[i] = semCaseBranchRange(c, t, b, covered)
     else:
       # constant sets and arrays are allowed:
-      var r = semConstExpr(c, b)
+      # set expected type to selector type for type inference
+      # even if it can be a different type like a set or array
+      var r = semConstExpr(c, b, expectedType = t[0].typ)
       if r.kind in {nkCurly, nkBracket} and r.len == 0 and branch.len == 2:
         # discarding ``{}`` and ``[]`` branches silently
         delSon(branch, 0)