fix issue #17132 in pants, created test case

CONTRIBUTORS.md

@@ -420,3 +420,4 @@ Created as part of the release process.
 + yjabri
 + Éric Jacob
 + Ólafur Páll Geirsson
++ Shubham Kumar Barnwal

src/python/pants/engine/target.py

@@ -569,6 +569,25 @@ def validate(self) -> None:
         context. If the validation only makes sense for certain goals acting on targets; those
         validations should be done in the associated rules.
         """
+        sources_field_types = tuple(
+            ft for ft in self.field_types if issubclass(ft, SourcesField)
+        )
+        if len(sources_field_types) > 1:
+            field_desc = ", ".join(
+                f"`{ft.alias}` ({ft.__name__})"
+                for ft in sorted(sources_field_types, key=lambda f: f.alias)
+            )
+            raise InvalidFieldException(
+                softwrap(
+                    f"""
+                    The {self.alias} target at {self.address} has multiple fields that subclass
+                    `SourcesField`, which is not supported: APIs such as `tgt.get(SourcesField)`
+                    require at most one. Found: {field_desc}.
+
+                    Remove or consolidate the extra sources field(s).
+                    """
+                )
+            )
 
 
 def _validate_origin_sources_blocks(origin_sources_blocks: FrozenDict[str, SourceBlocks]) -> None:

src/python/pants/engine/target_test.py

@@ -471,6 +471,30 @@ def test_target_validate() -> None:
         FortranTarget({FortranVersion.alias: "bad"}, Address("", target_name="t"))
 
 
+def test_target_rejects_multiple_sources_fields() -> None:
+    """Regression test for https://github.com/pantsbuild/pants/issues/17132."""
+
+    class PrimarySources(MultipleSourcesField):
+        alias = "sources"
+        default = ("*.ext",)
+
+    class ExtraSources(MultipleSourcesField):
+        alias = "extra_sources"
+
+    class InvalidMultiSourcesTarget(Target):
+        alias = "invalid_multi_sources"
+        core_fields = (FortranVersion, PrimarySources, ExtraSources)
+
+    with pytest.raises(InvalidTargetException) as exc:
+        InvalidMultiSourcesTarget(
+            {FortranVersion.alias: "v1", PrimarySources.alias: ["a.ext"], ExtraSources.alias: ["b"]},
+            Address("", target_name="t"),
+        )
+    assert "multiple fields that subclass `SourcesField`" in str(exc.value)
+    assert "`extra_sources`" in str(exc.value)
+    assert "`sources`" in str(exc.value)
+
+
 def test_target_residence_dir() -> None:
     assert FortranTarget({}, Address("some_dir/subdir")).residence_dir == "some_dir/subdir"
     assert (