Build: Declare typing-extensions as a core dependency

pyproject.toml

@@ -43,7 +43,8 @@ dependencies = [
     "tenacity>=8.2.3",
     "pyroaring>=1.0.0",
     "cachetools>=5.5",
-    "zstandard>=0.13.0"
+    "zstandard>=0.13.0",
+    "typing-extensions>=4.4.0" # Self/override are imported at runtime on Python < 3.12
 ]
 
 [project.urls]

tests/test_version.py

@@ -28,3 +28,22 @@ def test_version_format() -> None:
         "This failure could be due to a recent version bump in the Pyiceberg library. "
         "Please ensure you have the latest version installed by rerunning `make install` command."
     )
+
+
+def test_typing_extensions_is_a_core_dependency() -> None:
+    # typing_extensions is imported unconditionally at import time (e.g. Self in
+    # pyiceberg/typedef.py, override in the catalog and IO modules), so it must be a
+    # core runtime dependency rather than only a development one.
+    from importlib import metadata
+
+    from packaging.requirements import Requirement
+    from packaging.utils import canonicalize_name
+
+    requirements = [Requirement(requirement) for requirement in metadata.requires("pyiceberg") or []]
+    # Core dependencies carry no environment marker; optional extras add "; extra == ...".
+    core_dependencies = {canonicalize_name(requirement.name) for requirement in requirements if requirement.marker is None}
+
+    assert canonicalize_name("typing-extensions") in core_dependencies, (
+        "typing-extensions must be declared in [project.dependencies] because it is imported at runtime; "
+        "found only these core dependencies: " + ", ".join(sorted(core_dependencies))
+    )