fixes #4097

compiler/semexprs.nim

@@ -74,8 +74,12 @@ proc semSymGenericInstantiation(c: PContext, n: PNode, s: PSym): PNode =
 
 proc inlineConst(n: PNode, s: PSym): PNode {.inline.} =
   result = copyTree(s.ast)
-  result.typ = s.typ
-  result.info = n.info
+  if result.isNil:
+    localError(n.info, "constant of type '" & typeToString(s.typ) & "' has no value")
+    result = newSymNode(s)
+  else:
+    result.typ = s.typ
+    result.info = n.info
 
 type
   TConvStatus = enum

compiler/seminst.nim

@@ -111,9 +111,9 @@ proc removeDefaultParamValues(n: PNode) =
         # not possible... XXX We don't solve this issue here.
         a.sons[L-1] = ast.emptyNode
 
-proc freshGenSyms(n: PNode, owner: PSym, symMap: var TIdTable) =
+proc freshGenSyms(n: PNode, owner, orig: PSym, symMap: var TIdTable) =
   # we need to create a fresh set of gensym'ed symbols:
-  if n.kind == nkSym and sfGenSym in n.sym.flags:
+  if n.kind == nkSym and sfGenSym in n.sym.flags and n.sym.owner == orig:
     let s = n.sym
     var x = PSym(idTableGet(symMap, s))
     if x == nil:
@@ -122,7 +122,7 @@ proc freshGenSyms(n: PNode, owner: PSym, symMap: var TIdTable) =
       idTablePut(symMap, s, x)
     n.sym = x
   else:
-    for i in 0 .. <safeLen(n): freshGenSyms(n.sons[i], owner, symMap)
+    for i in 0 .. <safeLen(n): freshGenSyms(n.sons[i], owner, orig, symMap)
 
 proc addParamOrResult(c: PContext, param: PSym, kind: TSymKind)
 
@@ -137,7 +137,7 @@ proc addProcDecls(c: PContext, fn: PSym) =
 
   maybeAddResult(c, fn, fn.ast)
 
-proc instantiateBody(c: PContext, n, params: PNode, result: PSym) =
+proc instantiateBody(c: PContext, n, params: PNode, result, orig: PSym) =
   if n.sons[bodyPos].kind != nkEmpty:
     inc c.inGenericInst
     # add it here, so that recursive generic procs are possible:
@@ -149,7 +149,7 @@ proc instantiateBody(c: PContext, n, params: PNode, result: PSym) =
         let param = params[i].sym
         if sfGenSym in param.flags:
           idTablePut(symMap, params[i].sym, result.typ.n[param.position+1].sym)
-    freshGenSyms(b, result, symMap)
+    freshGenSyms(b, result, orig, symMap)
     b = semProcBody(c, b)
     b = hloBody(c, b)
     n.sons[bodyPos] = transformBody(c.module, b, result)
@@ -165,7 +165,7 @@ proc fixupInstantiatedSymbols(c: PContext, s: PSym) =
       openScope(c)
       var n = oldPrc.ast
       n.sons[bodyPos] = copyTree(s.getBody)
-      instantiateBody(c, n, nil, oldPrc)
+      instantiateBody(c, n, nil, oldPrc, s)
       closeScope(c)
       popInfoContext()
 
@@ -312,7 +312,7 @@ proc generateInstance(c: PContext, fn: PSym, pt: TIdTable,
       pragma(c, result, n.sons[pragmasPos], allRoutinePragmas)
     if isNil(n.sons[bodyPos]):
       n.sons[bodyPos] = copyTree(fn.getBody)
-    instantiateBody(c, n, fn.typ.n, result)
+    instantiateBody(c, n, fn.typ.n, result, fn)
     sideEffectsCheck(c, result)
     paramsTypeCheck(c, result.typ)
   else:

tests/template/typedescids.nim

@@ -0,0 +1,17 @@
+discard """
+  output: '''2 3'''
+"""
+
+# bug #4097
+
+var i {.compileTime.} = 2
+
+template defineId*(t: typedesc): stmt =
+  const id {.genSym.} = i
+  static: inc(i)
+  proc idFor*(T: typedesc[t]): int {.inline, raises: [].} = id
+
+defineId(int8)
+defineId(int16)
+
+echo idFor(int8), " ", idFor(int16)