Remove AsyncField.validate_{pre,post}_hydration

There was no need for this premature abstraction. Instead, all validation should happen in the corresponding hydrate rule.

src/python/pants/engine/target.py

@@ -60,9 +60,11 @@ class SourcesResult:
 
         @rule
         def hydrate_sources(sources: Sources) -> SourcesResult:
-            sources.validate_pre_hydration()
+            # possibly validate `sources.raw_value`
+            ...
             result = await Get[Snapshot](PathGlobs(sources.raw_value))
-            sources.validate_post_hydration(result)
+            # possibly validate `result`
+            ...
             return SourcesResult(result)
 
 
@@ -74,22 +76,6 @@ def rules():
         sources = await Get[SourcesResult](Sources, my_tgt.get(Sources))
     """
 
-    def validate_pre_hydration(self) -> None:
-        """Any validation that can be done on the original `raw_value`.
-
-        It is cheaper to do any possible validation here, rather than in `validate_post_hydration`,
-        because we can short-circuit if an invariant is violated before incurring the expense of
-        hydration.
-        """
-
-    def validate_post_hydration(self, result: Any) -> None:
-        """Any validation that must be done after hydration by inspecting the result of that
-        hydration.
-
-        For example, a `PythonSources` field may validate that all hydrated source files end in
-        `.py`.
-        """
-
 
 _F = TypeVar("_F", bound=Field)
 

src/python/pants/engine/target_test.py

@@ -42,16 +42,6 @@ class HaskellSources(AsyncField):
     alias: ClassVar = "sources"
     raw_value: Optional[List[str]]
 
-    def validate_pre_hydration(self) -> None:
-        ensure_str_list(self.raw_value)
-
-    def validate_post_hydration(self, result: Snapshot) -> None:
-        non_haskell_sources = [fp for fp in result.files if PurePath(fp).suffix != ".hs"]
-        if non_haskell_sources:
-            raise ValueError(
-                f"Received non-Haskell sources in {self.alias}: {non_haskell_sources}."
-            )
-
 
 @dataclass(frozen=True)
 class HaskellSourcesResult:
@@ -60,9 +50,13 @@ class HaskellSourcesResult:
 
 @rule
 async def hydrate_haskell_sources(sources: HaskellSources) -> HaskellSourcesResult:
-    sources.validate_pre_hydration()
-    result = await Get[Snapshot](PathGlobs("*.hs"))
-    sources.validate_post_hydration(result)
+    # Validate before hydration
+    ensure_str_list(sources.raw_value)
+    result = await Get[Snapshot](PathGlobs(sources.raw_value))
+    # Validate after hydration
+    non_haskell_sources = [fp for fp in result.files if PurePath(fp).suffix != ".hs"]
+    if non_haskell_sources:
+        raise ValueError(f"Received non-Haskell sources in {sources.alias}: {non_haskell_sources}.")
     return HaskellSourcesResult(result)