V2 of input suggestions API.

src/textual/suggester.py

@@ -0,0 +1,84 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Iterable, Optional
+
+from .message import Message
+
+if TYPE_CHECKING:
+    from .widgets import Input
+
+
+@dataclass
+class SuggestionReady(Message):
+    """Sent when a completion suggestion is ready."""
+
+    input_value: str
+    """The input value that the suggestion was for."""
+    suggestion: str
+    """The string suggestion."""
+
+
+class Suggester(ABC):
+    """Defines how [inputs][textual.widgets.Input] generate completion suggestions.
+
+    To define a custom suggester, subclass `Suggester` and implement the async method
+    `get_suggestion`.
+    See [`SuggestFromList`][textual.suggester.SuggestFromList] for an example.
+    """
+
+    async def get(self, input: "Input", value: str) -> None:
+        """Used by [`Input`][textual.widgets.Input] to get completion suggestions.
+
+        Note:
+            When implementing custom suggesters, this method does not need to be
+            overridden.
+
+        Args:
+            input: The input widget that requested a suggestion.
+            value: The current input value to complete.
+        """
+        suggestion = await self.get_suggestion(value)
+        if suggestion is None:
+            return
+
+        input.post_message(SuggestionReady(value, suggestion))
+
+    @abstractmethod
+    async def get_suggestion(self, value: str) -> Optional[str]:
+        """Try to get a completion suggestion for the given input value.
+
+        Custom suggesters should implement this method.
+
+        Args:
+            value: The current value of the input widget.
+
+        Returns:
+            A valid suggestion or `None`.
+        """
+        raise NotImplementedError()
+
+
+class SuggestFromList(Suggester):
+    """Give completion suggestions based on a fixed list of options."""
+
+    def __init__(self, suggestions: Iterable[str]) -> None:
+        """Creates a suggester based off of a given iterable of possibilities.
+
+        Args:
+            suggestions: Valid suggestions sorted by decreasing priority.
+        """
+        self.suggestions = list(suggestions)
+
+    async def get_suggestion(self, value: str) -> Optional[str]:
+        """Gets a completion from the given possibilities.
+
+        Args:
+            value: The current value of the input widget.
+
+        Returns:
+            A valid suggestion or `None`.
+        """
+        for suggestion in self.suggestions:
+            if suggestion.startswith(value):
+                return suggestion
+        return None

src/textual/widgets/_input.py

@@ -16,6 +16,7 @@ from ..events import Blur, Focus, Mount
 from ..geometry import Size
 from ..message import Message
 from ..reactive import reactive
+from ..suggester import Suggester, SuggestionReady
 from ..widget import Widget
 
 
@@ -155,12 +156,8 @@ class Input(Widget, can_focus=True):
     _cursor_visible = reactive(True)
     password = reactive(False)
     max_size: reactive[int | None] = reactive(None)
-    suggestions = reactive[Optional[List[str]]](None)
-    """List of completion suggestions that are shown while the user types.
-
-    The precedence of the suggestions is inferred from the order of the list.
-    Set this to `None` or to an empty list to disable this feature..
-    """
+    suggester: Suggester | None
+    """The suggester used to provide completions as the user types."""
     _suggestion = reactive("")
     """A completion suggestion for the current value in the input."""
 
@@ -213,7 +210,7 @@ class Input(Widget, can_focus=True):
         highlighter: Highlighter | None = None,
         password: bool = False,
         *,
-        suggestions: Iterable[str] | None = None,
+        suggester: Suggester | None = None,
         name: str | None = None,
         id: str | None = None,
         classes: str | None = None,
@@ -226,7 +223,8 @@ class Input(Widget, can_focus=True):
             placeholder: Optional placeholder text for the input.
             highlighter: An optional highlighter for the input.
             password: Flag to say if the field should obfuscate its content.
-            suggestions: Possible auto-completions for the input field.
+            suggester: [`Suggester`][textual.suggester.Suggester] associated with this
+                input instance.
             name: Optional name for the input widget.
             id: Optional ID for the widget.
             classes: Optional initial classes for the widget.
@@ -238,7 +236,7 @@ class Input(Widget, can_focus=True):
         self.placeholder = placeholder
         self.highlighter = highlighter
         self.password = password
-        self.suggestions = suggestions
+        self.suggester = suggester
 
     def _position_to_cell(self, position: int) -> int:
         """Convert an index within the value to cell position."""
@@ -285,8 +283,8 @@ class Input(Widget, can_focus=True):
 
     async def watch_value(self, value: str) -> None:
         self._suggestion = ""
-        if self.suggestions and value:
-            self._get_suggestion()
+        if self.suggester and value:
+            self.call_next(self.suggester.get, self, value)
         if self.styles.auto_dimensions:
             self.refresh(layout=True)
         self.post_message(self.Changed(self, value))
@@ -388,6 +386,11 @@ class Input(Widget, can_focus=True):
         else:
             self.cursor_position = len(self.value)
 
+    async def _on_suggestion_ready(self, event: SuggestionReady) -> None:
+        """Handle suggestion messages and set the suggestion when relevant."""
+        if event.input_value == self.value:
+            self._suggestion = event.suggestion
+
     def insert_text_at_cursor(self, text: str) -> None:
         """Insert new text at the cursor, move the cursor to the end of the new text.
 
@@ -531,23 +534,3 @@ class Input(Widget, can_focus=True):
     async def action_submit(self) -> None:
         """Handle a submit action (normally the user hitting Enter in the input)."""
         self.post_message(self.Submitted(self, self.value))
-
-    def validate_suggestions(
-        self, suggestions: Iterable[str] | None
-    ) -> list[str] | None:
-        """Convert suggestions iterable into a list."""
-        if suggestions is None:
-            return None
-        return list(suggestions)
-
-    @work(exclusive=True)
-    def _get_suggestion(self) -> None:
-        """Try to get a suggestion for the user."""
-        if not self.suggestions:
-            return
-
-        value = self.value
-        for suggestion in self.suggestions:
-            if suggestion.startswith(value):
-                self._suggestion = suggestion
-                break

tests/input/test_suggestions.py

@@ -3,13 +3,14 @@ import string
 import pytest
 
 from textual.app import App, ComposeResult
+from textual.suggester import SuggestFromList
 from textual.widgets import Input
 
 
 class SuggestionsApp(App[ComposeResult]):
-    def __init__(self, suggestions=None):
+    def __init__(self, suggestions):
         self.suggestions = suggestions
-        self.input = Input(suggestions=self.suggestions)
+        self.input = Input(suggester=SuggestFromList(self.suggestions))
         super().__init__()
 
     def compose(self) -> ComposeResult:
@@ -17,7 +18,7 @@ class SuggestionsApp(App[ComposeResult]):
 
 
 async def test_no_suggestions():
-    app = SuggestionsApp()
+    app = SuggestionsApp([])
     async with app.run_test() as pilot:
         assert app.input._suggestion == ""
         await pilot.press("a")

tests/snapshot_tests/snapshot_apps/input_suggestions.py

@@ -1,4 +1,5 @@
 from textual.app import App, ComposeResult
+from textual.suggester import SuggestFromList
 from textual.widgets import Input
 
 
@@ -14,7 +15,7 @@ class FruitsApp(App[None]):
     """
 
     def compose(self) -> ComposeResult:
-        yield Input("straw", suggestions=fruits)
+        yield Input("straw", suggester=SuggestFromList(fruits))
 
 
 if __name__ == "__main__":