Add get_child_by_id and get_widget_by_id (#1146)

* Add get_child_by_id and get_widget_by_id

* Remove redundant code

* Add unit tests for app-level get_child_by_id and get_widget_by_id

* Remove redundant test fixture injection

* Update CHANGELOG

* Enforce uniqueness of ID amongst widget children

* Enforce unique widget IDs amongst widgets mounted together

* Update CHANGELOG.md

* Ensuring unique IDs in a more logical place

* Add docstring to NodeList._get_by_id

* Dont use duplicate IDs in tests, dont mount 2000 widgets

* Mounting less widgets in a unit test

* Reword error message

* Use lower-level depth first search in get_widget_by_id to break out early

tests/test_dom.py

@@ -1,7 +1,6 @@
 import pytest
 
 from textual.css.errors import StyleValueError
-from textual.css.query import NoMatches
 from textual.dom import DOMNode, BadIdentifier
 
 
@@ -26,37 +25,6 @@ def test_display_set_invalid_value():
         node.display = "blah"
 
 
-@pytest.fixture
-def parent():
-    parent = DOMNode(id="parent")
-    child1 = DOMNode(id="child1")
-    child2 = DOMNode(id="child2")
-    grandchild1 = DOMNode(id="grandchild1")
-    child1._add_child(grandchild1)
-
-    parent._add_child(child1)
-    parent._add_child(child2)
-
-    yield parent
-
-
-def test_get_child_gets_first_child(parent):
-    child = parent.get_child(id="child1")
-    assert child.id == "child1"
-    assert child.get_child(id="grandchild1").id == "grandchild1"
-    assert parent.get_child(id="child2").id == "child2"
-
-
-def test_get_child_no_matching_child(parent):
-    with pytest.raises(NoMatches):
-        parent.get_child(id="doesnt-exist")
-
-
-def test_get_child_only_immediate_descendents(parent):
-    with pytest.raises(NoMatches):
-        parent.get_child(id="grandchild1")
-
-
 def test_validate():
     with pytest.raises(BadIdentifier):
         DOMNode(id="23")

tests/test_unmount.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from textual.app import App, ComposeResult
 from textual import events
 from textual.containers import Container

tests/test_widget.py

@@ -1,9 +1,13 @@
 import pytest
+import rich
 
-from textual.app import App
+from textual._node_list import DuplicateIds
+from textual.app import App, ComposeResult
 from textual.css.errors import StyleValueError
+from textual.css.query import NoMatches
+from textual.dom import DOMNode
 from textual.geometry import Size
-from textual.widget import Widget
+from textual.widget import Widget, MountError
 
 
 @pytest.mark.parametrize(
@@ -64,3 +68,92 @@ def test_widget_content_width():
     height = widget3.get_content_height(Size(20, 20), Size(80, 24), width)
     assert width == 3
     assert height == 3
+
+
+class GetByIdApp(App):
+    def compose(self) -> ComposeResult:
+        grandchild1 = Widget(id="grandchild1")
+        child1 = Widget(grandchild1, id="child1")
+        child2 = Widget(id="child2")
+
+        yield Widget(
+            child1,
+            child2,
+            id="parent",
+        )
+
+
+@pytest.fixture
+async def hierarchy_app():
+    app = GetByIdApp()
+    async with app.run_test():
+        yield app
+
+
+@pytest.fixture
+async def parent(hierarchy_app):
+    yield hierarchy_app.get_widget_by_id("parent")
+
+
+def test_get_child_by_id_gets_first_child(parent):
+    child = parent.get_child_by_id(id="child1")
+    assert child.id == "child1"
+    assert child.get_child_by_id(id="grandchild1").id == "grandchild1"
+    assert parent.get_child_by_id(id="child2").id == "child2"
+
+
+def test_get_child_by_id_no_matching_child(parent):
+    with pytest.raises(NoMatches):
+        parent.get_child_by_id(id="doesnt-exist")
+
+
+def test_get_child_by_id_only_immediate_descendents(parent):
+    with pytest.raises(NoMatches):
+        parent.get_child_by_id(id="grandchild1")
+
+
+def test_get_widget_by_id_no_matching_child(parent):
+    with pytest.raises(NoMatches):
+        parent.get_widget_by_id(id="i-dont-exist")
+
+
+def test_get_widget_by_id_non_immediate_descendants(parent):
+    result = parent.get_widget_by_id("grandchild1")
+    assert result.id == "grandchild1"
+
+
+def test_get_widget_by_id_immediate_descendants(parent):
+    result = parent.get_widget_by_id("child1")
+    assert result.id == "child1"
+
+
+def test_get_widget_by_id_doesnt_return_self(parent):
+    with pytest.raises(NoMatches):
+        parent.get_widget_by_id("parent")
+
+
+def test_get_widgets_app_delegated(hierarchy_app, parent):
+    # Check that get_child_by_id finds the parent, which is a child of the default Screen
+    queried_parent = hierarchy_app.get_child_by_id("parent")
+    assert queried_parent is parent
+
+    # Check that the grandchild (descendant of the default screen) is found
+    grandchild = hierarchy_app.get_widget_by_id("grandchild1")
+    assert grandchild.id == "grandchild1"
+
+
+def test_widget_mount_ids_must_be_unique_mounting_all_in_one_go(parent):
+    widget1 = Widget(id="hello")
+    widget2 = Widget(id="hello")
+
+    with pytest.raises(MountError):
+        parent.mount(widget1, widget2)
+
+
+def test_widget_mount_ids_must_be_unique_mounting_multiple_calls(parent):
+    widget1 = Widget(id="hello")
+    widget2 = Widget(id="hello")
+
+    parent.mount(widget1)
+    with pytest.raises(DuplicateIds):
+        parent.mount(widget2)

tests/test_widget_removing.py

@@ -15,18 +15,18 @@ async def test_remove_single_widget():
 async def test_many_remove_all_widgets():
     """It should be possible to remove all widgets on a multi-widget screen."""
     async with App().run_test() as pilot:
-        await pilot.app.mount(*[Static() for _ in range(1000)])
-        assert len(pilot.app.screen.children) == 1000
+        await pilot.app.mount(*[Static() for _ in range(10)])
+        assert len(pilot.app.screen.children) == 10
         await pilot.app.query(Static).remove()
         assert len(pilot.app.screen.children) == 0
 
 async def test_many_remove_some_widgets():
     """It should be possible to remove some widgets on a multi-widget screen."""
     async with App().run_test() as pilot:
-        await pilot.app.mount(*[Static(id=f"is-{n%2}") for n in range(1000)])
-        assert len(pilot.app.screen.children) == 1000
-        await pilot.app.query("#is-0").remove()
-        assert len(pilot.app.screen.children) == 500
+        await pilot.app.mount(*[Static(classes=f"is-{n%2}") for n in range(10)])
+        assert len(pilot.app.screen.children) == 10
+        await pilot.app.query(".is-0").remove()
+        assert len(pilot.app.screen.children) == 5
 
 async def test_remove_branch():
     """It should be possible to remove a whole branch in the DOM."""