Merge pull request #1548 from Textualize/fix-1477

Improve `Input` view position calculation

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - The styles `scrollbar-background-active` and `scrollbar-color-hover` are no longer ignored https://github.com/Textualize/textual/pull/1480
 - The widget `Placeholder` can now have its width set to `auto` https://github.com/Textualize/textual/pull/1508
+- Behavior of widget `Input` when rendering after programmatic value change and related scenarios https://github.com/Textualize/textual/issues/1477 https://github.com/Textualize/textual/issues/1443
 
 ## [0.9.1] - 2022-12-30
 

src/textual/widgets/_input.py

@@ -148,6 +148,11 @@ class Input(Widget, can_focus=True):
 
     def watch_cursor_position(self, cursor_position: int) -> None:
         width = self.content_size.width
+        if width == 0:
+            # If the input has no width the view position can't be elsewhere.
+            self.view_position = 0
+            return
+
         view_start = self.view_position
         view_end = view_start + width
         cursor_offset = self._cursor_offset

tests/test_input.py

@@ -0,0 +1,99 @@
+from rich.console import Console
+from textual.app import App
+from textual.widgets import Input
+
+
+async def test_input_value_visible_on_instantiation():
+    """Check if the full input value is rendered if the input is instantiated with it."""
+
+    class MyApp(App):
+        def compose(self):
+            yield Input(value="value")
+
+    app = MyApp()
+    async with app.run_test():
+        console = Console(width=5)
+        with console.capture() as capture:
+            console.print(app.query_one(Input).render())
+        assert capture.get() == "value"
+
+
+async def test_input_value_visible_after_value_assignment():
+    """Check if the full input value is rendered if the value is assigned to programmatically."""
+
+    class MyApp(App):
+        def compose(self):
+            yield Input()
+
+        def on_mount(self):
+            self.query_one(Input).value = "value"
+
+    app = MyApp()
+    async with app.run_test():
+        console = Console(width=5)
+        with console.capture() as capture:
+            console.print(app.query_one(Input).render())
+        assert capture.get() == "value"
+
+
+async def test_input_value_visible_if_mounted_later():
+    """Check if full input value is rendered if the widget is mounted later."""
+
+    class MyApp(App):
+        BINDINGS = [("a", "add_input", "add_input")]
+
+        def action_add_input(self):
+            self.mount(Input(value="value"))
+
+    app = MyApp()
+    async with app.run_test() as pilot:
+        await pilot.press("a")
+        console = Console(width=5)
+        with console.capture() as capture:
+            console.print(app.query_one(Input).render())
+        assert capture.get() == "value"
+
+
+async def test_input_value_visible_if_mounted_later_and_focused():
+    """Check if full input value is rendered if the widget is mounted later and immediately focused."""
+
+    class MyApp(App):
+        BINDINGS = [("a", "add_input", "add_input")]
+
+        def action_add_input(self):
+            inp = Input(value="value")
+            self.mount(inp)
+            inp.focus()
+
+    app = MyApp()
+    async with app.run_test() as pilot:
+        await pilot.press("a")
+        console = Console(width=5)
+        with console.capture() as capture:
+            console.print(app.query_one(Input).render())
+        assert capture.get() == "value"
+
+
+async def test_input_value_visible_if_mounted_later_and_assigned_after():
+    """Check if full value rendered if the widget is mounted later and the value is then assigned to."""
+
+    class MyApp(App):
+        BINDINGS = [
+            ("a", "add_input", "add_input"),
+            ("v", "set_value", "set_value"),
+        ]
+
+        def action_add_input(self):
+            self.mount(Input())
+
+        def action_set_value(self):
+            self.query_one(Input).value = "value"
+
+    app = MyApp()
+    async with app.run_test() as pilot:
+        await pilot.press("a")
+        await pilot.press("v")
+        console = Console(width=5)
+        with console.capture() as capture:
+            console.print(app.query_one(Input).render())
+        assert capture.get() == "value"