fix!: InputFilter clears TextField when an invalid character is entered

[ndonkoHenri]

Description

Fixes #3769

A custom FilteringTextInputFormatter has been created to prevent non-matching characters from causing the deletion of the whole field content.

Breaking Change

Solving this issue resulted to a breaking change: most of the regex_strings must be updated to use anchors.

Why?

This is caused by RegExp.hasMatch() allowing non-matching characters to be entered/visible (without replacement), as long as the field content contains a matching substring.

Migration

Use start(^) and end($) anchors in the pattern/regexString:

• r"[a-zA-Z]" -> r"^[a-zA-Z]*$"
• r"[0-9]" -> r"^[0-9]*$"

In the above cases, the * is important, else it will be impossible to delete the last character in the field.

AI Prompt

To ease migration, below is a simple prompt that can be useful:

Help me update the following regex pattern: ####### 
Ensure the entire string matches the pattern and allows for an empty string. 

Test Code

import flet as ft


def main(page: ft.Page):

    page.add(
        ft.TextField(
            label="Ex: 2244.89",
            keyboard_type=ft.KeyboardType.NUMBER,
            input_filter=ft.InputFilter(
                allow=True,
                regex_string=r"^\d*(\.\d{0,2})?$",
                replacement_string="",
            ),
        )
    )


ft.app(target=main)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Summary by Sourcery

Fix issue where InputFilter clears TextField when an invalid character is entered by introducing CustomFilteringTextInputFormatter. This change requires updating most regex_strings to use start (^) and end ($) anchors to ensure proper matching.

Bug Fixes:

• Prevent InputFilter from clearing the entire TextField content when an invalid character is entered.

Enhancements:

• Introduce CustomFilteringTextInputFormatter to handle input filtering with more control over regex patterns and matching behavior.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request addresses issue #3769 by introducing a custom FilteringTextInputFormatter to prevent invalid characters from clearing the entire TextField content. The changes include the creation of CustomFilteringTextInputFormatter and CustomNumberFormatter classes, updates to the InputFilter class to support additional regex options, and modifications to default filters to use anchored patterns. These changes result in a breaking change, requiring updates to existing regex_strings to use start (^) and end ($) anchors.

File-Level Changes

Files	Changes
packages/flet/lib/src/utils/textfield.dart packages/flet/lib/src/controls/textfield.dart	Introduced custom input formatters (CustomFilteringTextInputFormatter and CustomNumberFormatter) to handle specific filtering and formatting logic.
sdk/python/packages/flet-core/src/flet_core/textfield.py	Enhanced InputFilter class to support additional regex options and updated default filters to use anchored patterns.

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[sourcery-ai]

Hey @ndonkoHenri - I've reviewed your changes and found some issues that need to be addressed.

Blocking issues:

• Hard-coded regex pattern found. (link)
• Hard-coded regex pattern found. (link)

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🔴 Security: 2 blocking issues
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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