Error in pass2 for type MyExceptionTypeException, error: duplicate entry 'get_Message' in method table

[nbevans]

Repro steps

    exception InitializeException of Message : string

Expected behavior

The exception type doesn't throw an exception at build time.

Actual behavior

It throws:

FSC : error FS2014: A problem occurred writing the binary 'C:\Sandbox\Singapore\Singapore.Mobile.Storage\obj\Debug\netstandard2.0\Singapore.Mobile.Storage.dll': Error in pass2 for type Singapore.Mobile.Storage.Tasks, error: Error in pass2 for type DataSet, error: Error in pass2 for type InitializeException, error: duplicate entry 'get_Message' in method table [C:\Sandbox\Singapore\Singapore.Mobile.Storage\Singapore.Mobile.Storage.fsproj]

Known workarounds

Change the exception type to:

exception InitializeException of MessageText : string

Related information
This is a regression that occurred after updating to VS 17.4.0

[vzarytovskii]

It's caused by one of the features enabled by default in F# 7, adding a Message property.

Should probably be a better message, or even not generate if it's already there.

[vzarytovskii]

This is very similar to
#14321

We can either chose to not generate it if the field is present, or produce a similar issue. It is a breaking change, technically, but guarded by language version.

Update: since it's guarded by language flag (7) and fails to compile now, I think I will do the following change - if the 'Message' property is present on the exception, compiler will produce the warning that it will "overwrite" the builtin one, and will not emit builtin one.

[vzarytovskii]

Interesting enough, we're checking members apparently, but it fails the check for exn it seems

 let ilMethodDefs =
            [ ilCtorDef
              yield! ilCtorDefNoArgs
              yield! serializationRelatedMembers
              yield! ilMethodDefsForProperties

              if not (exnc.HasMember g "get_Message" []) && not (exnc.HasMember g "Message" [])  then
                  yield! GenPrintingMethod cenv eenv "get_Message" ilThisTy m ]