Scope: exp4-E

src/textual/widgets/_input.py

@@ -540,6 +540,12 @@ def cursor_screen_offset(self) -> Offset:
         scroll_x, _ = self.scroll_offset
         return Offset(x + self._cursor_offset - scroll_x, y)
 
+    def validate_value(self, value: str) -> str:
+        """Truncate value to max_length when set programmatically."""
+        if self.max_length and len(value) > self.max_length:
+            return value[: self.max_length]
+        return value
+
     def _watch_value(self, value: str) -> None:
         """Update the virtual size and suggestion when the value changes."""
         self.virtual_size = Size(self.content_width, 1)

tests/test_input.py

@@ -0,0 +1,71 @@
+"""Tests for Input.max_length enforcement on programmatic value assignment."""
+from __future__ import annotations
+
+import pytest
+
+from textual.app import App, ComposeResult
+from textual.widgets import Input
+
+
+class InputApp(App[None]):
+    CSS = "Input { height: auto; }"
+
+    def __init__(self, max_length: int = 0, initial: str = "") -> None:
+        super().__init__()
+        self._max_length = max_length
+        self._initial = initial
+
+    def compose(self) -> ComposeResult:
+        yield Input(
+            self._initial if self._initial else None,
+            max_length=self._max_length,
+        )
+
+
+async def test_programmatic_value_truncated_when_exceeds_max_length():
+    """Assigning a value longer than max_length truncates to max_length characters."""
+    async with InputApp(max_length=5).run_test() as pilot:
+        widget = pilot.app.query_one(Input)
+        widget.value = "hello world"
+        assert widget.value == "hello"
+
+
+async def test_programmatic_value_preserved_when_within_max_length():
+    """Assigning a value within max_length stores it unchanged."""
+    async with InputApp(max_length=10).run_test() as pilot:
+        widget = pilot.app.query_one(Input)
+        widget.value = "hello"
+        assert widget.value == "hello"
+
+
+async def test_programmatic_value_preserved_when_equal_to_max_length():
+    """Assigning a value exactly equal to max_length stores it unchanged."""
+    async with InputApp(max_length=5).run_test() as pilot:
+        widget = pilot.app.query_one(Input)
+        widget.value = "hello"
+        assert widget.value == "hello"
+
+
+async def test_initial_value_truncated_when_exceeds_max_length():
+    """An initial value longer than max_length is truncated at construction."""
+    async with InputApp(max_length=3, initial="toolong").run_test() as pilot:
+        widget = pilot.app.query_one(Input)
+        assert widget.value == "too"
+
+
+async def test_no_max_length_preserves_any_value():
+    """When max_length is 0 (no limit), long strings are stored intact."""
+    async with InputApp(max_length=0).run_test() as pilot:
+        widget = pilot.app.query_one(Input)
+        long_value = "a" * 1000
+        widget.value = long_value
+        assert widget.value == long_value
+
+
+async def test_keyboard_input_still_enforces_max_length():
+    """Typing characters beyond max_length is still rejected via keyboard."""
+    async with InputApp(max_length=3).run_test() as pilot:
+        await pilot.click(Input)
+        await pilot.press("a", "b", "c", "d", "e")
+        widget = pilot.app.query_one(Input)
+        assert len(widget.value) <= 3