Expose standard Rust traits on FFI error types

[spacebear21]

This fixes the string representation of the FFI errors to use the Rust Display string instead of an opaque Instance of *Error message. See #1264 (comment) for more context.

Discovered and authored with Claude.

Pull Request Checklist

Please confirm the following before requesting review:

• I have disclosed my use of
  AI
  in the body of this PR.
• I have read CONTRIBUTING.md and rebased my branch to produce hygienic commits.

[coveralls]

Coverage Report for CI Build 24527851470

Coverage remained the same at 84.38%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

---

Coverage Stats

Relevant Lines:	12766
Covered Lines:	10772
Line Coverage:	84.38%
Coverage Strength:	413.48 hits per line

---

💛 - Coveralls

[spacebear21]

The dart error here looks unrelated to the changes in this PR, @chavic can you confirm?

[codaMW]

Reviewed the changes. Exposing Display, Error, and Debug on FFI error types is the right move, this makes them usable with anyhow and ? in Rust glue code, and improves error messages for FFI consumers.

One small question: the PR description mentions fixing "Instance of *Error" strings. Is this primarily improving the Dart/Kotlin/Swift binding experience? Might be helpful to note in the commit body.

Regarding the unrelated Dart CI failure, agreed it's pre-existing and not related to this change.
utACK.

[benalleng]

The dart error here looks unrelated to the changes in this PR, @chavic can you confirm?

This seems to relate to the errors being turned to "Exception" like in the early stage of #1428 (comment)

[spacebear21]

This seems to relate to the errors being turned to "Exception" like in the early stage of #1428 (comment)

Yep, confirmed that updating uniffi-dart to the latest git rev fixes the issue and added this in a9e0cab.

[benalleng]

TACK 4d2855c

I added some dummy Display tests to visualize the errors in python with the following tests.

Python Display Tests

class TestErrorDisplay(unittest.TestCase):
    def test_address_parse_error_display(self):
        try:
            payjoin.ReceiverBuilder(
                "not-an-address",
                "https://example.com",
                payjoin.OhttpKeys.decode(bytes.fromhex(
                    "01001604ba48c49c3d4a92a3ad00ecc63a024da10ced02180c73ec12d8a7ad2cc91bb483824fe2bee8d28bfe2eb2fc6453bc4d31cd851e8a6540e86c5382af588d370957000400010003"
                )),
            )
            self.fail("expected error")
        except payjoin.ReceiverBuilderError as e:
            msg = str(e)
            self.assertNotIn("Instance of", msg)
            self.assertTrue(len(msg) > 0)

    def test_sender_input_error_display(self):
        uri = payjoin.Uri.parse(
            "bitcoin:tb1q6d3a2w975yny0asuvd9a67ner4nks58ff0q8g4?pj=https://example.com/pj"
        ).check_pj_supported()
        try:
            payjoin.SenderBuilder("not-a-psbt", uri)
            self.fail("expected error")
        except payjoin.SenderInputError as e:
            self.assertNotIn("Instance of", str(e))

    def test_pj_parse_error_display(self):
        try:
            payjoin.Uri.parse("not-a-uri")
            self.fail("expected error")
        except payjoin.PjParseError as e:
            print(f"\ntype={type(e).__name__}")
            print(f"{str(e)!r}")
            print(f"{repr(e)!r}")
            self.assertIn("Error parsing the payjoin URI", str(e)) 

Saw this response.

$ uv run python -m unittest test.test_payjoin_unit_test.TestErrorDisplay.test_pj_parse_error_display -v test_pj_parse_error_display (test.test_payjoin_unit_test.TestErrorDisplay.test_pj_parse_error_display) ... 
type=PjParseError
'Error parsing the payjoin URI: invalid BIP21 URI'
'PjParseError { msg: "invalid BIP21 URI" }'
ok

Not right now but I think it would be really nice to get some error Display test coverage in payjoin soon maybe as a v1.1 milestone

[caarloshenriq]

tACK 4d2855c

Ran the Python Display tests from @benalleng locally after regenerating the bindings:

test_address_parse_error_display ... ok
test_pj_parse_error_display ...

type=PjParseError
'Error parsing the payjoin URI: invalid BIP21 URI'
'PjParseError { msg: "invalid BIP21 URI" }'
ok
test_sender_input_error_display ... ok

[spacebear21]

I think it would be really nice to get some error Display test coverage in payjoin soon maybe as a v1.1 milestone

Agreed, we should also start thinking about a strategy for cross-testing these things across the all downstream language bindings. Maybe we can pull out test inputs and expected results into shared test vectors to loop over in each language's test module, or something like that.