Add Vyper 0.5.0a3 support

AGENTS.md

@@ -31,6 +31,8 @@ feature, not an optional smoke check.
   source material for migrations.
 - `docs/migration-coverage.md` — mapping from each syntax-history entry to an
   automated rule, diagnostic, explicit no-op, or validation-only behavior.
+- [`DEVELOPMENT.md`](DEVELOPMENT.md) — maintainer setup, architecture,
+  rule-writing, corpus, and release workflow reference.
 - `scripts/corpus.py` — corpus import, dedupe, and compiler-backed smoke tooling.
 - `scripts/smoke-wheel.sh` — package smoke test used by CI and publish workflows.
 

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+- Added opt-in support for targeting Vyper `0.5.0a3`; custom error syntax is
+  treated as newly accepted source and broad alpha pragmas compile with `a3`
+  when needed.
+
 ## 0.4.1 - 2026-06-06
 
 - Fixed standard-json corpus imports so only declared compilation targets are

README.md

@@ -6,9 +6,9 @@ rewrite is safe by compiling the source and the result and comparing their ABI,
 method identifiers, and storage layout.
 
 It covers installable Vyper `0.1.0b*` prereleases through `0.4.3`, plus opt-in
-`0.5.0a1` and `0.5.0a2` alpha targets. Rules are version-gated: a given rewrite
-only fires when the migration from the source version to the target version
-actually crosses the compiler release that introduced the change.
+`0.5.0a1` through `0.5.0a3` alpha targets. Rules are version-gated: a given
+rewrite only fires when the migration from the source version to the target
+version actually crosses the compiler release that introduced the change.
 
 ## Install
 
@@ -46,7 +46,7 @@ vyupgrade contracts/ --check
 ```
 
 The target defaults to `0.4.3`; pass `--target-version` to migrate to a
-different release, including an explicit alpha target such as `0.5.0a2`.
+different release, including an explicit alpha target such as `0.5.0a3`.
 
 Paths may be files or directories; directories are searched recursively for
 `.vy` and `.vyi` sources. The source version is inferred per file from its
@@ -135,7 +135,7 @@ diagnostic instead of being applied.
   change mapped to a rule, diagnostic, explicit no-op, or validation-only
   behavior.
 - [docs/vyper-syntax-history.md](docs/vyper-syntax-history.md) — the versioned
-  Vyper syntax history from `0.5.0a2` back through the `0.1.0b*` prereleases,
+  Vyper syntax history from `0.5.0a3` back through the `0.1.0b*` prereleases,
   with PR links and before/after examples.
 - [CHANGELOG.md](CHANGELOG.md) — release notes.
 - [DEVELOPMENT.md](DEVELOPMENT.md) — maintainer validation and release workflow.

docs/migration-coverage.md

@@ -20,6 +20,11 @@ modern Python interpreter.
 
 ## v0.5.x prereleases
 
+### v0.5.0a3
+
+- Custom errors added: no-op. This is newly accepted revert declaration and
+  raising syntax; existing string revert reasons remain valid.
+
 ### v0.5.0a2
 
 - Docstring-only function bodies rejected: `VY131` inserts an explicit `pass`

docs/vyper-syntax-history.md

@@ -1,6 +1,6 @@
 # Vyper Syntax History
 
-This document tracks Vyper source syntax changes from `v0.5.0a2` back through
+This document tracks Vyper source syntax changes from `v0.5.0a3` back through
 the installable `v0.1.0-beta.*` prereleases. It is intended as upgrade source
 material for `vyupgrade`.
 
@@ -12,6 +12,28 @@ runtime semantic changes unless they require source text to change.
 
 ## v0.5.x prereleases
 
+### v0.5.0a3
+
+Release: <https://github.com/vyperlang/vyper/releases/tag/v0.5.0a3>
+
+- Custom errors added. [#4791](https://github.com/vyperlang/vyper/pull/4791)
+
+  Before:
+
+  ```vyper
+  # No contract-defined custom error declaration syntax.
+  raise "unauthorized"
+  ```
+
+  After:
+
+  ```vyper
+  error Unauthorized:
+      caller: address
+
+  raise Unauthorized(caller=msg.sender)
+  ```
+
 ### v0.5.0a2
 
 Release: <https://github.com/vyperlang/vyper/releases/tag/v0.5.0a2>

src/vyupgrade/versions.py

@@ -11,7 +11,7 @@
 # PyPI has no final 0.1.0 release; these are the installable Vyper releases before 0.2.1.
 LEGACY_PRERELEASE_VERSIONS = tuple(f"0.1.0b{number}" for number in range(1, 18))
 LEGACY_PRERELEASES = frozenset(Version(version) for version in LEGACY_PRERELEASE_VERSIONS)
-ALPHA_RELEASE_VERSIONS = ("0.5.0a1", "0.5.0a2")
+ALPHA_RELEASE_VERSIONS = ("0.5.0a1", "0.5.0a2", "0.5.0a3")
 ALPHA_RELEASES = frozenset(Version(version) for version in ALPHA_RELEASE_VERSIONS)
 
 
@@ -142,6 +142,8 @@ def _source_syntax_floor(source: str) -> VyperVersion | None:
         floors.append(Version("0.3.7"))
     if re.search(r"\bsend\s*\([^)]*\bgas\s*=", source):
         floors.append(Version("0.3.8"))
+    if re.search(r"(?m)^\s*error\s+[A-Za-z_][A-Za-z0-9_]*\s*:", source):
+        floors.append(Version("0.5.0a3"))
     return max(floors) if floors else None
 
 

tests/test_versions.py

@@ -26,6 +26,7 @@ def test_known_versions_cover_full_supported_range() -> None:
     assert is_supported_source_version("0.4.3")
     assert is_supported_source_version("0.5.0a1")
     assert is_supported_source_version("0.5.0a2")
+    assert is_supported_source_version("0.5.0a3")
     assert not is_supported_source_version("0.1.0")
     assert not is_supported_source_version("0.1.0b18")
     assert not is_supported_source_version("0.1.0b99")
@@ -36,6 +37,7 @@ def test_known_versions_cover_full_supported_range() -> None:
     assert VyperVersion("0.2.1") in known_versions_satisfying(">=0.2.1,<0.2.3")
     assert VyperVersion("0.4.3") in known_versions_satisfying(">=0.4.0")
     assert VyperVersion("0.5.0a2") in known_versions_satisfying(">=0.5.0a1,<0.5.0")
+    assert VyperVersion("0.5.0a3") in known_versions_satisfying(">=0.5.0a1,<0.5.0")
 
 
 def test_version_specs_pick_lowest_satisfying_source_floor() -> None:
@@ -48,6 +50,7 @@ def test_version_specs_pick_lowest_satisfying_source_floor() -> None:
     assert compiler_version_for_spec("<=0.3.10") == "0.3.10"
     assert compiler_version_for_spec(">=0.5.0a1,<0.5.0") == "0.5.0a1"
     assert compiler_version_for_spec("<=0.5.0a2") == "0.5.0a2"
+    assert compiler_version_for_spec("<=0.5.0a3") == "0.5.0a3"
 
 
 def test_source_syntax_hints_raise_broad_pragma_compiler_floor() -> None:
@@ -60,6 +63,12 @@ def test_source_syntax_hints_raise_broad_pragma_compiler_floor() -> None:
     assert compiler_version_for_source("^0.3.0", "send(self.owner, fee, gas=msg.gas)") == "0.3.8"
     assert compiler_version_for_source(">=0.3.8,<0.4.0", "TOKEN: immutable(address)") == "0.3.8"
     assert compiler_version_for_source(">=0.3.0,<0.3.4", "enum Side:\n    BUY\n") == "0.3.0"
+    assert (
+        compiler_version_for_source(
+            ">=0.5.0a1,<0.5.0", "error Unauthorized:\n    caller: address\n"
+        )
+        == "0.5.0a3"
+    )
 
 
 def test_migration_context_tracks_patch_level_crossings() -> None: