Handling of Encoded in Meta conversions

[ExpHP]

[ExpHP]

Option 1: Add Encoding as context to ToMeta/FromMeta

Advantages:

Changes are generally straightforward to make.

Problems with this solution:

• Big signature changes. ToMeta becomes fallible.

   pub trait FromMeta<'a>: Sized {
  -    fn from_meta(meta: &'a Sp<Meta>) -> Result<Self, FromMetaError<'a>>;
  +    fn from_meta(meta: &'a Sp<Meta>, cfg: &FromMetaContext) -> Result<Self, FromMetaError<'a>>;
   }
   pub trait ToMeta {
  +    fn to_meta(&self, cfg: &ToMetaContext) -> Result<Meta, SimpleError>;
   }
  

• Annoyingness of cfg in impls:
  • .get_field(cfg, "field")
  • If we try to eliminate the cfg parameter of get_field by adding &'a FromMetaContext to ParseObject then we end up with annoying lifetime problems due to impl FnOnce(&mut ParseObject) parameters. Either need to make it ParseObject<'a, 'c>, or we need to make FromMeta take &'a FromMetaContext.
• FromMeta needs a Custom(crate::error::CompileError), variant.

[ExpHP]

Option 2: AnmFile<S> and similar

Summary

• compile/decompile will use AnmFile<String>
• write_to_stream/read_from_stream will use AnmFile<Encoded>

Advantages:

• Changes are made almost exclusively to anm.rs, std.rs, msg.rs, and cli_defs.rs.
• We might want a separate pass for conversion of args to blobs? This could go hand-in-hand with that. (and then that would be the only pass that needs to know anything about the encoding; nice separation of concerns)

Problems with this solution:

• How will we do these errors if the "subdir/file.png" is now an Encoded string of unknown encoding?

  error: entry for 'subdir/file.png' is missing required field 'width'!
         (if this data is available in an existing anm file, try using `-i ANM_FILE`)