Conformance tests failing due to unrecognized encoding

[nirosys]

We currently have 17 conformance test failures due to unrecognized encodings.

Failed test files:

 % cat conformance_test_failures_update_3.json | jq -r '.[] | [to_entries[] | .key as $key | .value[] | select(.result // "" | . != "Ok") | {path: $key, error: .error}] | [.[] | select(.error | contains("unrecognized encoding"))][].path' | sort | uniq -c
   1 ./ion-tests/conformance/demos/metaprogramming.ion
   2 ./ion-tests/conformance/eexp/binary/argument_encoding.ion
  13 ./ion-tests/conformance/eexp/binary/tagless_types.ion
   1 ./ion-tests/conformance/system_macros/delta.ion

Unrecognized encodings:

% cat conformance_test_failures_update_3.json | jq -r '.[] | [to_entries[] | .key as $key | .value[] | select(.result // "" | . != "Ok") | {path: $key, error: .error}] | [.[] | select(.error | contains("unrecognized encoding"))][].error' | sed -Ee "s/.*encoding '([a-z0-9_]+)'.*/\1/" | sort | uniq -c
   2 flex_int
   1 flex_sym
   1 float16
   1 float32
   1 float64
   1 int16
   1 int32
   1 int64
   2 int8
   2 uint16
   1 uint32
   1 uint64
   2 uint8

Encodings

• uint8 - Implement uint8 tagless encoding #991
• uint16 - Implement remaining tagless uints #993
• uint32 - Implement remaining tagless uints #993
• uint64 - Implement remaining tagless uints #993
• int8
• int16
• int32
• int64
• flex_int
• flex_sym
• float16
• float32
• float64

[nirosys]

After adding support for a tagless encoding, conformance tests end up failing due to how encoding context is currently being handled:

Source: ion-tests/conformance/eexp/binary/tagless_types.ion
Test  : a macro with a uint8 parameter
Error : PANIC: PanicHookInfo { payload: Any { .. }, location: Location { file: "tests/conformance_dsl/fragment.rs", line: 523, col: 30 }, can_unwind: true, force_no_backtrace: false }

This failure is from the populating of the macro table after a first-pass read to discover the macros. The macros created in tagless_types.ion are given a null name which ends up causing this expect to fail.