Update to pydantic 2

The pydantic usage here is pretty light, so the changes needed aren't
that dramatic.

* The dataclass `__post_init_post_parse__` method is no longer supported
  and simply `__post_init__` should be used.

* `TypeError` is no longer converted to `ValidationError` in validators,
  so just use `ValueError`.

* The `@validator` decorator has changed to `@field_decorator` with a
  minor change in parameters.

* Validator error messages now include the error type, which means
  `Value error` for all of our validators.

* The `ValidationError.errors()` detail list now has a custom
  `ErrorDetail` type. This exposes the fact that the `loc` attribute is
  actually a tuple of `str` and `int`. Mypy flags that as an issue if an
  `int` is passed to `str.join`. We don't actually have any cases where
  an `int` would occur, but copy a converter from the documentation so
  it's handled correctly in case that does happen.

This also allows dropping the mypy upper version pin as updated Pydantic
contains the necessary compatibility fix.

https://docs.pydantic.dev/2.7/migration/

Pipfile

@@ -8,7 +8,7 @@ python_version = "3.11"
 flake8 = "*"
 flake8-bugbear = "*"
 freezegun = "*"
-mypy = ">=0.720, < 0.920"
+mypy = ">=0.720"
 pytest = "*"
 pytest-aiohttp = "*"
 pytest-asyncio = "*"
@@ -18,7 +18,7 @@ types-toml = "*"
 [packages]
 aiohttp = ">= 3.5.0"
 aioredis = "~= 1.3"
-pydantic = ">= 1.1, < 1.9"
+pydantic = "~= 2.7"
 toml = "*"
 
 [scripts]

azafea_metrics_proxy/config/__init__.py

@@ -23,11 +23,11 @@
 import dataclasses
 import logging
 import os
-from typing import Any, Dict, List, MutableMapping
+from typing import Any, List, MutableMapping
 
-from pydantic.class_validators import validator
+from pydantic import field_validator, ValidationError
 from pydantic.dataclasses import dataclass
-from pydantic.error_wrappers import ValidationError
+from pydantic_core import ErrorDetails
 
 import toml
 
@@ -40,18 +40,32 @@
 
 
 class InvalidConfigurationError(Exception):
-    def __init__(self, errors: List[Dict[str, Any]]) -> None:
+    def __init__(self, errors: List[ErrorDetails]) -> None:
         self.errors = errors
 
     def __str__(self) -> str:
         msg = ['Invalid configuration:']
 
         for e in self.errors:
-            loc = e['loc']
-            msg.append(f"* {'.'.join(loc)}: {e['msg']}")
+            loc = self._loc_str(e)
+            msg.append(f"* {loc}: {e['msg']}")
 
         return '\n'.join(msg)
 
+    # The loc field in ErrorDetails is a tuple of strings and ints.
+    # https://docs.pydantic.dev/latest/errors/errors/#customize-error-messages
+    @staticmethod
+    def _loc_str(details: ErrorDetails) -> str:
+        path = ''
+        for i, element in enumerate(details['loc']):
+            if isinstance(element, str):
+                if i > 0:
+                    path += '.'
+                path += element
+            else:  # pragma: no cover (our config does not use lists)
+                path += f'[{element}]'
+        return path
+
 
 class NoSuchConfigurationError(AttributeError):
     pass
@@ -66,7 +80,7 @@ def __getattr__(self, name: str) -> Any:
 class Main(_Base):
     verbose: bool = False
 
-    @validator('verbose', pre=True)
+    @field_validator('verbose', mode='before')
     def verbose_is_boolean(cls, value: Any) -> bool:
         return is_boolean(value)
 
@@ -78,11 +92,11 @@ class Redis(_Base):
     password: str = DEFAULT_PASSWORD
     ssl: bool = False
 
-    @validator('host', pre=True)
+    @field_validator('host', mode='before')
     def host_is_non_empty_string(cls, value: Any) -> str:
         return is_non_empty_string(value)
 
-    @validator('port', pre=True)
+    @field_validator('port', mode='before')
     def port_is_strictly_positive_integer(cls, value: Any) -> int:
         return is_strictly_positive_integer(value)
 
@@ -92,7 +106,7 @@ class Config(_Base):
     main: Main = dataclasses.field(default_factory=Main)
     redis: Redis = dataclasses.field(default_factory=Redis)
 
-    def __post_init_post_parse__(self) -> None:
+    def __post_init__(self) -> None:
         self.warn_about_default_passwords()
 
     @classmethod