make `genericsOpenSym` work at instantiation time, new behavior in `openSym` (#24111)

alternative to #24101

#23892 changed the opensym experimental switch so that it has to be
enabled in the context of the generic/template declarations capturing
the symbols, not the context of the instantiation of the
generics/templates. This was to be in line with where the compiler gives
the warnings and changes behavior in a potentially breaking way.

However `results` [depends on the old
behavior](https://github.com/arnetheduck/nim-results/blob/71d404b314479a6205bfd050f4fe5fe49cdafc69/results.nim#L1428),
so that the callers of the macros provided by results always take
advantage of the opensym behavior. To accomodate this, we change the
behavior of the old experimental option that `results` uses,
`genericsOpenSym`, so that ignores the information of whether or not
symbols are intentionally opened and always gives the opensym behavior
as long as it's enabled at instantiation time. This should keep
`results` working as is. However this differs from the normal opensym
switch in that it doesn't generate `nnkOpenSym`.

Before it was just a generics-only version of `openSym` along with
`templateOpenSym` which was only for templates. So `templateOpenSym` is
removed along with this change, but no one appears to have used it.

5 files changed, 23 insertions, 15 deletions

diff --git a/compiler/condsyms.nim b/compiler/condsyms.nim
index 3119e657e..5043fc5d4 100644
--- a/compiler/condsyms.nim
+++ b/compiler/condsyms.nim
@@ -167,4 +167,5 @@ proc initDefines*(symbols: StringTableRef) =
 
   defineSymbol("nimHasVtables")
   defineSymbol("nimHasGenericsOpenSym2")
+  defineSymbol("nimHasGenericsOpenSym3")
   defineSymbol("nimHasJsNoLambdaLifting")
diff --git a/compiler/options.nim b/compiler/options.nim
index 44196609a..b77bdd2a3 100644
--- a/compiler/options.nim
+++ b/compiler/options.nim
@@ -226,8 +226,8 @@ type
     strictCaseObjects,
     inferGenericTypes,
     openSym, # remove nfDisabledOpenSym when this is default
-    # separated alternatives to above:
-    genericsOpenSym, templateOpenSym,
+    # alternative to above:
+    genericsOpenSym
     vtables
 
   LegacyFeature* = enum
diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index c90aa991b..41493b046 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -187,6 +187,7 @@ proc semOpenSym(c: PContext, n: PNode, flags: TExprFlags, expectedType: PType,
           break
       o = o.owner
   # nothing found
+  n.flags.excl nfDisabledOpenSym
   if not warnDisabled and isSym:
     result = semExpr(c, n, flags, expectedType)
   else:
@@ -197,7 +198,9 @@ proc semOpenSym(c: PContext, n: PNode, flags: TExprFlags, expectedType: PType,
 
 proc semSymChoice(c: PContext, n: PNode, flags: TExprFlags = {}, expectedType: PType = nil): PNode =
   if n.kind == nkOpenSymChoice:
-    result = semOpenSym(c, n, flags, expectedType, warnDisabled = nfDisabledOpenSym in n.flags)
+    result = semOpenSym(c, n, flags, expectedType,
+      warnDisabled = nfDisabledOpenSym in n.flags and
+        genericsOpenSym notin c.features)
     if result != nil:
       return
   result = n
@@ -3293,8 +3296,12 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}, expectedType: PType
   of nkSym:
     let s = n.sym
     if nfDisabledOpenSym in n.flags:
-      let res = semOpenSym(c, n, flags, expectedType, warnDisabled = true)
-      assert res == nil
+      let override = genericsOpenSym in c.features
+      let res = semOpenSym(c, n, flags, expectedType,
+        warnDisabled = not override)
+      if res != nil:
+        assert override
+        return res
     # because of the changed symbol binding, this does not mean that we
     # don't have to check the symbol for semantics here again!
     result = semSym(c, n, s, flags)
diff --git a/compiler/semgnrc.nim b/compiler/semgnrc.nim
index 16bb7f094..2639aba6c 100644
--- a/compiler/semgnrc.nim
+++ b/compiler/semgnrc.nim
@@ -74,7 +74,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
     else:
       result = symChoice(c, n, s, scOpen)
       if canOpenSym(s):
-        if {openSym, genericsOpenSym} * c.features != {}:
+        if openSym in c.features:
           if result.kind == nkSym:
             result = newOpenSym(result)
           else:
@@ -112,7 +112,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
         # we are in a generic context and `prepareNode` will be called
         result = newSymNodeTypeDesc(s, c.idgen, n.info)
         if canOpenSym(result.sym):
-          if {openSym, genericsOpenSym} * c.features != {}:
+          if openSym in c.features:
             result = newOpenSym(result)
           else:
             result.flags.incl nfDisabledOpenSym
@@ -122,7 +122,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
     else:
       result = newSymNodeTypeDesc(s, c.idgen, n.info)
       if canOpenSym(result.sym):
-        if {openSym, genericsOpenSym} * c.features != {}:
+        if openSym in c.features:
           result = newOpenSym(result)
         else:
           result.flags.incl nfDisabledOpenSym
@@ -141,7 +141,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
         return
       result = newSymNodeTypeDesc(s, c.idgen, n.info)
       if canOpenSym(result.sym):
-        if {openSym, genericsOpenSym} * c.features != {}:
+        if openSym in c.features:
           result = newOpenSym(result)
         else:
           result.flags.incl nfDisabledOpenSym
@@ -153,7 +153,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
       # we are in a generic context and `prepareNode` will be called
       result = newSymNodeTypeDesc(s, c.idgen, n.info)
       if canOpenSym(result.sym):
-        if {openSym, genericsOpenSym} * c.features != {}:
+        if openSym in c.features:
           result = newOpenSym(result)
         else:
           result.flags.incl nfDisabledOpenSym
@@ -164,7 +164,7 @@ proc semGenericStmtSymbol(c: PContext, n: PNode, s: PSym,
   else:
     result = newSymNode(s, n.info)
     if canOpenSym(result.sym):
-      if {openSym, genericsOpenSym} * c.features != {}:
+      if openSym in c.features:
         result = newOpenSym(result)
       else:
         result.flags.incl nfDisabledOpenSym
diff --git a/compiler/semtempl.nim b/compiler/semtempl.nim
index 7546d095d..8bc68728c 100644
--- a/compiler/semtempl.nim
+++ b/compiler/semtempl.nim
@@ -233,7 +233,7 @@ proc semTemplSymbol(c: var TemplCtx, n: PNode, s: PSym; isField, isAmbiguous: bo
   of OverloadableSyms:
     result = symChoice(c.c, n, s, scOpen, isField)
     if not isField and result.kind in {nkSym, nkOpenSymChoice}:
-      if {openSym, templateOpenSym} * c.c.features != {}:
+      if openSym in c.c.features:
         if result.kind == nkSym:
           result = newOpenSym(result)
         else:
@@ -246,7 +246,7 @@ proc semTemplSymbol(c: var TemplCtx, n: PNode, s: PSym; isField, isAmbiguous: bo
     else:
       result = newSymNodeTypeDesc(s, c.c.idgen, n.info)
       if not isField and s.owner != c.owner:
-        if {openSym, templateOpenSym} * c.c.features != {}:
+        if openSym in c.c.features:
           result = newOpenSym(result)
         else:
           result.flags.incl nfDisabledOpenSym
@@ -264,7 +264,7 @@ proc semTemplSymbol(c: var TemplCtx, n: PNode, s: PSym; isField, isAmbiguous: bo
       if not isField and not (s.owner == c.owner and
           s.typ != nil and s.typ.kind == tyGenericParam) and
           result.kind in {nkSym, nkOpenSymChoice}:
-        if {openSym, templateOpenSym} * c.c.features != {}:
+        if openSym in c.c.features:
           if result.kind == nkSym:
             result = newOpenSym(result)
           else:
@@ -277,7 +277,7 @@ proc semTemplSymbol(c: var TemplCtx, n: PNode, s: PSym; isField, isAmbiguous: bo
     else:
       result = newSymNode(s, n.info)
       if not isField:
-        if {openSym, templateOpenSym} * c.c.features != {}:
+        if openSym in c.c.features:
           result = newOpenSym(result)
         else:
           result.flags.incl nfDisabledOpenSym