Add some TS style "utility types"

Author: msullivan

scripts/update-examples.sh

@@ -14,3 +14,6 @@ scripts/py2rst.py tests/test_fastapilike_2.py --start "Begin PEP section: Automa
 
 scripts/py2rst.py tests/test_nplike.py --start "Begin PEP section" --end "End PEP section" \
   | scripts/rst_replace_section.py "$PEP" pep827-numpy-impl -i
+
+scripts/py2rst.py tests/test_ts_utility.py --start "Begin PEP section" --end "End PEP section" \
+  | scripts/rst_replace_section.py "$PEP" pep827-ts-utils -i

tests/test_ts_utility.py

@@ -0,0 +1,121 @@
+# mypy: ignore-errors
+"""
+TypeScript-style utility type operators: Pick, Omit, Partial.
+
+See https://www.typescriptlang.org/docs/handbook/utility-types.html
+"""
+
+import textwrap
+from typing import Literal, NotRequired, TypedDict
+
+import typemap_extensions as typing
+from typemap.type_eval import eval_typing
+
+from . import format_helper
+
+
+# The "Todo" type from the TypeScript utility-types examples
+class Todo:
+    title: str
+    description: str
+    completed: bool
+
+
+class TodoTD(TypedDict):
+    title: str
+    description: str
+    completed: bool
+
+
+# Begin PEP section: Utility types
+"""
+TypeScript defines a number of `utility types
+<https://www.typescriptlang.org/docs/handbook/utility-types.html>`__
+for performing common type operations.
+
+We present implementations of a selection of them::
+
+"""
+
+
+# Pick<T, Keys>
+# Constructs a type by picking the set of properties Keys from T.
+type Pick[T, Keys] = typing.NewProtocol[
+    *[
+        p
+        for p in typing.Iter[typing.Members[T]]
+        if typing.IsAssignable[p.name, Keys]
+    ]
+]
+
+# Omit<T, Keys>
+# Constructs a type by picking all properties from T and then removing Keys.
+type Omit[T, Keys] = typing.NewProtocol[
+    *[
+        p
+        for p in typing.Iter[typing.Members[T]]
+        if not typing.IsAssignable[p.name, Keys]
+    ]
+]
+
+# Partial<T>
+# Constructs a type with all properties of T set to optional (T | None).
+type Partial[T] = typing.NewProtocol[
+    *[
+        typing.Member[p.name, p.type | None, p.quals]
+        for p in typing.Iter[typing.Attrs[T]]
+    ]
+]
+
+# PartialTD<T>
+# Like Partial, but for TypedDicts: wraps all fields in NotRequired
+# rather than making them T | None.
+type PartialTD[T] = typing.NewProtocol[
+    *[
+        typing.Member[p.name, NotRequired[p.type], p.quals]
+        for p in typing.Iter[typing.Attrs[T]]
+    ]
+]
+# End PEP section: Utility types
+
+
+def test_pick():
+    tgt = eval_typing(Pick[Todo, Literal["title"] | Literal["completed"]])
+    fmt = format_helper.format_class(tgt)
+    assert fmt == textwrap.dedent("""\
+        class Pick[tests.test_ts_utility.Todo, typing.Literal['title'] | typing.Literal['completed']]:
+            title: str
+            completed: bool
+    """)
+
+
+def test_omit():
+    tgt = eval_typing(Omit[Todo, Literal["description"]])
+    fmt = format_helper.format_class(tgt)
+    assert fmt == textwrap.dedent("""\
+        class Omit[tests.test_ts_utility.Todo, typing.Literal['description']]:
+            title: str
+            completed: bool
+    """)
+
+
+def test_partial():
+    tgt = eval_typing(Partial[Todo])
+    fmt = format_helper.format_class(tgt)
+    assert fmt == textwrap.dedent("""\
+        class Partial[tests.test_ts_utility.Todo]:
+            title: str | None
+            description: str | None
+            completed: bool | None
+    """)
+
+
+def test_partial_td():
+    tgt = eval_typing(PartialTD[TodoTD])
+    fmt = format_helper.format_class(tgt)
+    assert fmt == textwrap.dedent("""\
+        class PartialTD[tests.test_ts_utility.TodoTD]:
+            title: typing.NotRequired[str]
+            description: typing.NotRequired[str]
+            completed: typing.NotRequired[bool]
+    """)