fix semcase on tySequence and tyObject #20283 #19682 (#20339)

* fix semcase on tySequence and tyObject #20283 #19682

* use better arg name

* avoiding returns nil use errorNode instead, clean code

* use efNoDiagnostics flag

* remove tests/errmsgs/t19682.nim

* combine 2 test cases to one file

compiler/semcall.nim

@@ -402,6 +402,9 @@ proc resolveOverloads(c: PContext, n, orig: PNode,
     if overloadsState == csEmpty and result.state == csEmpty:
       if efNoUndeclared notin flags: # for tests/pragmas/tcustom_pragma.nim
         template impl() =
+          result.state = csNoMatch
+          if efNoDiagnostics in flags:
+            return
           # xxx adapt/use errorUndeclaredIdentifierHint(c, n, f.ident)
           localError(c.config, n.info, getMsgDiagnostic(c, flags, n, f))
         if n[0].kind == nkIdent and n[0].ident.s == ".=" and n[2].kind == nkIdent:

compiler/semdata.nim

@@ -73,6 +73,7 @@ type
     efSkipFieldVisibilityCheck
       # Use this if undeclared identifiers should not raise an error during
       # overload resolution.
+    efNoDiagnostics
 
   TExprFlags* = set[TExprFlag]
 

compiler/semstmts.nim

@@ -1004,7 +1004,7 @@ proc handleCaseStmtMacro(c: PContext; n: PNode; flags: TExprFlags): PNode =
   toResolve.add n[0]
 
   var errors: CandidateErrors
-  var r = resolveOverloads(c, toResolve, toResolve, {skTemplate, skMacro}, {},
+  var r = resolveOverloads(c, toResolve, toResolve, {skTemplate, skMacro}, {efNoDiagnostics},
                            errors, false)
   if r.state == csMatch:
     var match = r.calleeSym
@@ -1017,7 +1017,11 @@ proc handleCaseStmtMacro(c: PContext; n: PNode; flags: TExprFlags): PNode =
     case match.kind
     of skMacro: result = semMacroExpr(c, toExpand, toExpand, match, flags)
     of skTemplate: result = semTemplateExpr(c, toExpand, match, flags)
-    else: result = nil
+    else: result = errorNode(c, n[0])
+  elif r.state == csNoMatch:
+    result = errorNode(c, n[0])
+  if result.kind == nkEmpty:
+    localError(c.config, n[0].info, errSelectorMustBeOfCertainTypes)
   # this would be the perfectly consistent solution with 'for loop macros',
   # but it kinda sucks for pattern matching as the matcher is not attached to
   # a type then:
@@ -1088,12 +1092,8 @@ proc semCase(c: PContext, n: PNode; flags: TExprFlags; expectedType: PType = nil
   else:
     popCaseContext(c)
     closeScope(c)
-    #if caseStmtMacros in c.features:
-    result = handleCaseStmtMacro(c, n, flags)
-    if result != nil:
-      return result
-    localError(c.config, n[0].info, errSelectorMustBeOfCertainTypes)
-    return
+    return handleCaseStmtMacro(c, n, flags)
+
   for i in 1..<n.len:
     setCaseContextIdx(c, i)
     var x = n[i]

tests/errmsgs/tcase_stmt.nim

@@ -0,0 +1,29 @@
+discard """
+  cmd: "nim check --hints:off $file"
+  errormsg: ""
+  nimout: '''
+tcase_stmt.nim(22, 7) Error: selector must be of an ordinal type, float or string
+tcase_stmt.nim(28, 6) Error: selector must be of an ordinal type, float or string
+
+
+
+
+
+
+
+'''
+"""
+
+
+
+# bug #19682
+type A = object
+
+case A()
+else:
+  discard
+
+# bug #20283
+
+case @[]
+else: discard