implements: "Allow bycopy to work in params #21874" (#21877)

* implements: "Allow bycopy to work in params #21874"

* Update compiler/pragmas.nim

---------

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>

compiler/ast.nim

@@ -231,7 +231,7 @@ type
   TNodeKinds* = set[TNodeKind]
 
 type
-  TSymFlag* = enum    # 50 flags!
+  TSymFlag* = enum    # 51 flags!
     sfUsed,           # read access of sym (for warnings) or simply used
     sfExported,       # symbol is exported from module
     sfFromGeneric,    # symbol is instantiation of a generic; this is needed
@@ -313,6 +313,7 @@ type
                       # This is disallowed but can cause the typechecking to go into
                       # an infinite loop, this flag is used as a sentinel to stop it.
     sfVirtual         # proc is a C++ virtual function
+    sfByCopy          # param is marked as pass bycopy
 
   TSymFlags* = set[TSymFlag]
 

compiler/ccgutils.nim

@@ -122,8 +122,10 @@ proc ccgIntroducedPtr*(conf: ConfigRef; s: PSym, retType: PType): bool =
   var pt = skipTypes(s.typ, typedescInst)
   assert skResult != s.kind
   
+  #note precedence: params override types
   if optByRef in s.options: return true
-  if tfByRef in pt.flags: return true
+  elif sfByCopy in s.flags: return false 
+  elif tfByRef in pt.flags: return true
   elif tfByCopy in pt.flags: return false
   case pt.kind
   of tyObject:

compiler/pragmas.nim

@@ -84,7 +84,7 @@ const
     wGensym, wInject,
     wIntDefine, wStrDefine, wBoolDefine, wDefine,
     wCompilerProc, wCore}
-  paramPragmas* = {wNoalias, wInject, wGensym, wByRef}
+  paramPragmas* = {wNoalias, wInject, wGensym, wByRef, wByCopy}
   letPragmas* = varPragmas
   procTypePragmas* = {FirstCallConv..LastCallConv, wVarargs, wNoSideEffect,
                       wThread, wRaises, wEffectsOf, wLocks, wTags, wForbids, wGcSafe,
@@ -1204,7 +1204,9 @@ proc singlePragma(c: PContext, sym: PSym, n: PNode, i: var int,
           incl(sym.typ.flags, tfByRef)
       of wByCopy:
         noVal(c, it)
-        if sym.kind != skType or sym.typ == nil: invalidPragma(c, it)
+        if sym.kind == skParam:
+          incl(sym.flags, sfByCopy)
+        elif sym.kind != skType or sym.typ == nil: invalidPragma(c, it)
         else: incl(sym.typ.flags, tfByCopy)
       of wPartial:
         noVal(c, it)