fix #1858; Add support for generic templates and macros

Implementation notes:
Just after overload resolution, the resolved generic params will be added to the
call expression to be later processed in evalTemplate and evalMacroCall. These
procs have been modified to handle the increased number of parameters, but one
remaining issue is that immediate templates and macros don't go through the same
process. The next commit will outlaw the use of generic parameters with such macros.

compiler/seminst.nim

@@ -10,14 +10,10 @@
 # This module implements the instantiation of generic procs.
 # included from sem.nim
 
-proc instantiateGenericParamList(c: PContext, n: PNode, pt: TIdTable,
-                                 entry: var TInstantiation) = 
-  if n.kind != nkGenericParams: 
-    internalError(n.info, "instantiateGenericParamList; no generic params")
-  newSeq(entry.concreteTypes, n.len)
+iterator instantiateGenericParamList(c: PContext, n: PNode, pt: TIdTable): PSym =
+  internalAssert n.kind == nkGenericParams
   for i, a in n.pairs:
-    if a.kind != nkSym: 
-      internalError(a.info, "instantiateGenericParamList; no symbol")
+    internalAssert a.kind == nkSym
     var q = a.sym
     if q.typ.kind notin {tyTypeDesc, tyGenericParam, tyStatic, tyIter}+tyTypeClasses:
       continue
@@ -42,8 +38,7 @@ proc instantiateGenericParamList(c: PContext, n: PNode, pt: TIdTable,
       #t = ReplaceTypeVarsT(cl, t)
     s.typ = t
     if t.kind == tyStatic: s.ast = t.n
-    addDecl(c, s)
-    entry.concreteTypes[i] = t
+    yield s
 
 proc sameInstantiation(a, b: TInstantiation): bool =
   if a.concreteTypes.len == b.concreteTypes.len:
@@ -196,7 +191,7 @@ proc generateInstance(c: PContext, fn: PSym, pt: TIdTable,
   ## The `pt` parameter is a type-unsafe mapping table used to link generic
   ## parameters to their concrete types within the generic instance.
   # no need to instantiate generic templates/macros:
-  if fn.kind in {skTemplate, skMacro}: return fn
+  internalAssert fn.kind notin {skMacro, skTemplate}
   # generates an instantiated proc
   if c.instCounter > 1000: internalError(fn.ast.info, "nesting too deep")
   inc(c.instCounter)
@@ -213,12 +208,18 @@ proc generateInstance(c: PContext, fn: PSym, pt: TIdTable,
   result.ast = n
   pushOwner(result)
   openScope(c)
-  internalAssert n.sons[genericParamsPos].kind != nkEmpty
+  let gp = n.sons[genericParamsPos]
+  internalAssert gp.kind != nkEmpty
   n.sons[namePos] = newSymNode(result)
   pushInfoContext(info)
   var entry = TInstantiation.new
   entry.sym = result
-  instantiateGenericParamList(c, n.sons[genericParamsPos], pt, entry[])
+  newSeq(entry.concreteTypes, gp.len)
+  var i = 0
+  for s in instantiateGenericParamList(c, gp, pt):
+    addDecl(c, s)
+    entry.concreteTypes[i] = s.typ
+    inc i
   pushProcCon(c, result)
   instantiateProcType(c, pt, result, info)
   n.sons[genericParamsPos] = ast.emptyNode