Check for duplicate tag URIs at compile time

README.md

@@ -15,8 +15,6 @@ an overview of already available features.
    - Support generic objects
    - Support transient fields (i.e. fields that will not be (de-)serialized on
      objects and tuples)
-   - Check for and avoid name clashes when generating local tags for custom
-     object types.
 
 ## Developers
 

yaml.nim

@@ -633,9 +633,19 @@ var
     ## Should not be modified manually. Will be extended by
     ## `serializable <#serializable,stmt,stmt>`_.
 
+static:
+  var
+    registeredUris {.compileTime.} = newSeq[string]() ## \
+      ## Since Table doesn't really work at compile time, we also store 
+      ## registered URIs here to be able to generate a static compiler error 
+      ## when the user tries to register an URI more than once.
+
 template setTagUriForType*(t: typedesc, uri: string): stmt =
   ## Associate the given uri with a certain type. This uri is used as YAML tag
   ## when loading and dumping values of this type.
+  when uri in registeredUris:
+    {. fatal: "[NimYAML] URI \"" & uri & "\" registered twice!" .}
+  static: registeredUris.add(uri)
   let id {.gensym.} = serializationTagLibrary.registerUri(uri)
   proc yamlTag*(T: typedesc[t]): TagId {.inline, raises: [].} = id
     ## autogenerated
@@ -644,10 +654,29 @@ template setTagUriForType*(t: typedesc, uri: string, idName: expr): stmt =
   ## Like `setTagUriForType <#setTagUriForType,typedesc,string>`_, but lets
   ## you choose a symbol for the `TagId <#TagId>`_ of the uri. This is only
   ## necessary if you want to implement serialization / construction yourself.
+  when uri in registeredUris:
+    {. fatal: "[NimYAML] URI \"" & uri & "\" registered twice!" .}
+  static: registeredUris.add(uri)
   let idName* = serializationTagLibrary.registerUri(uri)
   proc yamlTag*(T: typedesc[t]): TagId {.inline, raises: [].} = idName
     ## autogenerated
 
+static:
+  # standard YAML tags used by serialization
+  registeredUris.add("!")
+  registeredUris.add("?")
+  registeredUris.add("tag:yaml.org,2002:str")
+  registeredUris.add("tag:yaml.org,2002:null")
+  registeredUris.add("tag:yaml.org,2002:bool")
+  registeredUris.add("tag:yaml.org,2002:float")
+  registeredUris.add("tag:yaml.org,2002:timestamp")
+  registeredUris.add("tag:yaml.org,2002:value")
+  registeredUris.add("tag:yaml.org,2002:binary")
+  # special tags used by serialization
+  registeredUris.add("!nim:field")
+  registeredUris.add("!nim:nil:string")
+  registeredUris.add("!nim:nil:seq")
+
 # tags for Nim's standard types
 setTagUriForType(char, "!nim:system:char", yTagNimChar)
 setTagUriForType(int8, "!nim:system:int8", yTagNimInt8)