implemented strictCaseObjects (#20608)

* implemented strictCaseObjects

* changelog update

compiler/guards.nim

@@ -1054,8 +1054,12 @@ proc buildProperFieldCheck(access, check: PNode; o: Operators): PNode =
     assert check.getMagic == mNot
     result = buildProperFieldCheck(access, check[1], o).neg(o)
 
-proc checkFieldAccess*(m: TModel, n: PNode; conf: ConfigRef) =
+proc checkFieldAccess*(m: TModel, n: PNode; conf: ConfigRef; produceError: bool) =
   for i in 1..<n.len:
     let check = buildProperFieldCheck(n[0], n[i], m.g.operators)
     if check != nil and m.doesImply(check) != impYes:
-      message(conf, n.info, warnProveField, renderTree(n[0])); break
+      if produceError:
+        localError(conf, n.info, "field access outside of valid case branch: " & renderTree(n[0]))
+      else:
+        message(conf, n.info, warnProveField, renderTree(n[0]))
+      break

compiler/options.nim

@@ -217,7 +217,8 @@ type
     strictEffects,
     unicodeOperators, # deadcode
     flexibleOptionalParams,
-    strictDefs
+    strictDefs,
+    strictCaseObjects
 
   LegacyFeature* = enum
     allowSemcheckedAstModification,

compiler/sempass2.nim

@@ -665,7 +665,7 @@ proc trackCase(tracked: PEffects, n: PNode) =
   let stringCase = n[0].typ != nil and skipTypes(n[0].typ,
         abstractVarRange-{tyTypeDesc}).kind in {tyFloat..tyFloat128, tyString, tyCstring}
   let interesting = not stringCase and interestingCaseExpr(n[0]) and
-        tracked.config.hasWarn(warnProveField)
+        (tracked.config.hasWarn(warnProveField) or strictCaseObjects in tracked.c.features)
   var inter: TIntersection = @[]
   var toCover = 0
   for i in 1..<n.len:
@@ -1049,8 +1049,8 @@ proc track(tracked: PEffects, n: PNode) =
     for i in 0..<n.len: track(tracked, n[i])
   of nkCheckedFieldExpr:
     track(tracked, n[0])
-    if tracked.config.hasWarn(warnProveField):
-      checkFieldAccess(tracked.guards, n, tracked.config)
+    if tracked.config.hasWarn(warnProveField) or strictCaseObjects in tracked.c.features:
+      checkFieldAccess(tracked.guards, n, tracked.config, strictCaseObjects in tracked.c.features)
   of nkTryStmt: trackTryStmt(tracked, n)
   of nkPragma: trackPragmaStmt(tracked, n)
   of nkAsgn, nkFastAsgn, nkSinkAsgn: