bugfix: allow tuple constructors in generic code

compiler/semgnrc.nim

@@ -306,6 +306,9 @@ proc semGenericStmt(c: PContext, n: PNode,
     n.sons[bodyPos] = semGenericStmtScope(c, body, flags, toBind)
     closeScope(c.tab)
   of nkPragma, nkPragmaExpr: nil
+  of nkExprColonExpr:
+    checkMinSonsLen(n, 2)
+    result.sons[1] = semGenericStmt(c, n.sons[1], flags, toBind)
   else: 
     for i in countup(0, sonsLen(n) - 1): 
       result.sons[i] = semGenericStmt(c, n.sons[i], flags, toBind)

tests/run/trettypeinference.nim

@@ -6,12 +6,16 @@ discard """
 import typetraits
 
 proc plus(a, b): auto = a + b
+proc makePair(a, b): auto = (first: a, second: b)
 
 proc `+`(a, b: string): seq[string] = @[a, b]
 
 var i = plus(10, 20)
 var s = plus("A", "B")
 
+var p = makePair("key", 100)
+static: assert p[0].type is string
+
 echo i.type.name
 echo s.type.name